Please help me tune my control room….please.

JasonC · Post by **JasonC** » Wed Oct 28, 2015 5:17 pm

Hello,
I've just about completed my new studio north of Atlanta, GA. All construction is complete, I have my occupancy permit, and have moved the basics in to the studio. All thats left to do before opening my new doors for business is small bells and whistles…. and the long-dreaded acoustical tuning process to get the control room and live rooms up to snuff and sounding great! This is where I need help. I understand basic room acoustics theories and practices. But I've never actually "target-tuned" a room for maximum performance. I've done my homework researching the use of absorbers and diffusers, scatter plates and resonators, calculators and analyzers, etc., but not having much experience in target tuning and knowing that trying to do so without the proper data and someone that knows how to translate that data into something understandable is basically a total crap shoot. And an expensive one.

That Is why I'm asking all the humble and very helpful acoustical gurus that reside here on the Sayers' forum for some help interpreting my data and helping me fix my rooms' issues.

Right now, the control room is my main focus. Here's a basic description…
The room at its max width and length is 14' 3" W x 19' 10" L. The max height is 10' high for the front 16' of the room and it drops down to 8' over the back 4'. Offset 1' 6" from the room width's center, the front walls splay out at 30 degrees to the max width. I have sketch up drawings and pictures on another computer that I can upload upon request of the room. I have basic 2" 703 absorbers up on the walls in the RFZ area and spaced on the side walls deeper in the room, a cloud over the mix position, and a 4" 703 absorber across the back wall along with two 20" super chunk bass traps in the corners. The floor, although built over a crawl space, is as massive as I could make it using 1/2" durock(on green glue), a pretty thick layer of thin set and some heavy porcelain tile. Finished with two thin rugs, one under the mix position and one at the rear of the room. I knew I was gonna need some basic absorption regardless so thats where I started. In total there's about 370 square feet of 703 surface coverage throughout the room. I arranged my mix position in the front 1/3rd of the room, set up my basic workstation and started listening. I'll provide some precise measurements of speaker placement and mix position upon request.
Right off the bat I noticed two things.. 1) the room sounds too dead. The upper mid to high range is a bit dull. When I put on a mix and just take a few steps outside the door into the next room that's has nothing in it the music sounds excellent, inside its like there's a little vacuum slightly sucking out the punch and sparkle of the sound. I figure I either have too much absorption or I don't have it in the right places around the room. And 2) in the mix position the bass… well the bass sucks. I've gotten somewhat familiar with REW and have taken some basic measurements of the room. Although I dont fully comprehend all of the data(would love some help in that department) I've still managed to get the basic readings on the rooms frequency response. In the mix position my shots show that I have a nice sized dip at about 64-67hz and a peak at about 113-120. It doesn't take an analyzer to be able to tell. The upper lows are quite exaggerated listening to mixes. A few feet behind the mix position things sound fairly balanced in the bass range, and in the back of the room things sound fairly balanced also but still lacking some highs.
So basically I need help properly locating my mix position and speakers to work with the room better, locating my absorption in the room properly and most likely adding some reflections back in with diffusers or scatter plates, and building some tuned resonators, traps, or porous absorbers to fix my 120hz issue in the mix position. And Im really curious as to how to fix the 65hz dip in the mix position. I know you can tune traps to absorb targeted low frequencies like 65hz but reflecting them back in? Is that even possible?
If anyone's willing to help me get going in the right direction it would be greatly appreciated. I can provide all specific measurements and dimensions needed, drawings, REW measurements, etc. necessary to help get things properly calculated upon request.

Thanks to any and all willing to lend some knowledge and wisdom.

Jason

bert Stoltenborg · Post by **bert Stoltenborg** » Wed Oct 28, 2015 9:42 pm

Show us the measurements!

JasonC · Post by **JasonC** » Thu Oct 29, 2015 11:14 am

Sorry for not posting this last night with my first post but it was all on another computer.
Below is a wire drawing of my control room with dimensions of the room and speaker placement. The room height is 10' for the front 16' of the room and drops to 8' over the back 4' of the room. The speakers are 44" off the ground, same with mix position.

Jc CtrlRoom 1.jpg

I seem to be having trouble attaching the .mdat file from REW to this post. The file is 16MBs. Too large? Here is a link to WeTransfer where I have the .mdat file available for download….
http://we.tl/IThZSXMIPI
This link will only be active for 2 weeks so let me know if I need to reupoload or if this is not allowed. If there is a better way to go about posting the REW data here let me know.
I took several measurements for comparing. Mix Position Speakers L+R, Speaker L, Speaker R, 3' behind the mix position, 6' behind the mix position, and one near each rear corner of the room. If any of those are not necessary I can delete them to shrink the file size. Also please advise me if there are any other specific measurements I should take or if there's any info that I've left out in my wire drawing please let me know.
Anyone who can help me sift through this data would be a blessing.
Thanks!

Jc

Soundman2020 · Post by **Soundman2020** » Thu Oct 29, 2015 1:34 pm

H there Jason. It's good to see you back again! I always wondered what had happened, when your build thread suddenly went dead... So it really is good to see you here again!

OK, I really hope that what I'm going to say is not taken the wrong way! There's no way to break this to you gently, so I'll just blurt it right out:

What the hell happened???

... how on earth did your control room end up shaped like THAT???!!!

Your original plans were nothing at all like that, and neither was your build. What happened? Why did you chop off the front corners of the room, and move your speakers onto the desk? How come you did not soffit mount them? Why is the back of the room lower than the front? Why is the mix position located at the huge modal null point, of 25% of the room depth? Why is your head closer to the speaker than the distance between the speakers? Why are the speaker angles and locations wrong?

There's so much wrong in there that it's going to be hard to make it right, before you can start tuning anything!

Your MDAT file reveals the truth: you are seated in a huge null at 65 Hz, and the entire low end below about 90 Hz just isn't there. Then you have a mountainous peak at 110 Hz, that is easily 32 dB louder than the dip at 65 Hz. So there's more than a thousand times (literally: over 1,000 times) more energy at 110 Hz as there is at 65 Hz. That dip is very likely associated with your 0.0.1 axial mode.

the long-dreaded acoustical tuning process to get the control room and live rooms up to snuff and sounding great!

There's a big issue here: room tuning is not something you do at the end, after the room is built. Room tuning is something you do during the initial design process, when deciding on the dimensions, layout, geometry, and basic treatment. The only thing that can be done at this stage is final tweaking, but what I'm seeing in the MDAT file is far beyond the ability of final tweaking.

I have basic 2" 703 absorbers up on the walls in the RFZ area

What RFZ area? I don't see any RFZ area on your diagram. That's not an RFZ room, and there are clearly reflection points on the side walls. The reflections are clearly visible in the IR data (in the MDAT file). Perhaps you intended to build an RFZ room, but what is shown on that diagram is not an RFZ room.

I arranged my mix position in the front 1/3rd of the room,

Actually, you have it in the front 1/4 of the room!

In fact, your head is almost exactly at 25% of the room depth, right where the major peaks and nulls fall for all x.0.0 axial modes. That's about the worst possible location.

1) the room sounds too dead.

Correct. It is. Far too dead. Decay times are around 180 ms, but for a room that size should be around 220 - 250 ms. in theory, and personally I would shoot for even more, maybe 280 or so. In other words, your decay times should be at lest 25% longer, and perhaps as much as 60% longer. That's why it sounds dead.

I figure I either have too much absorption or I don't have it in the right places around the room.

Probably both, I would say. And you also don't have it at the right frequencies. Plus the frequency response is rather uneven, to say the least, and not just in the low end: all the way up to the mid range there are large variations.

And 2) in the mix position the bass… well the bass sucks.

Yes it does. Mostly because you are in a huge modal null, perhaps an SBIR issue as well.

I dont fully comprehend all of the data(would love some help in that department) I've still managed to get the basic readings on the rooms frequency response.

Frequency response is only a small part of the room acoustics. Time-domain issues are equally important if not more so, and so are reflections. Phase issues are another part of it. In REW, the RT60, Decay, Waterfall, and Spectrogram buttons give you a lot if information about time-domain issues: how sound decays over time in your room. IR tells you about reflections, decay, and several other things. "GD" is Group Delay, which is too complex to get into right now, and is the least of your worries anyway. Distortion is more for speaker designers than room tuners.

There are also three clearly visible acoustic "regions" or "zones" in your room, that decay at three different slopes. There's one region (probably at the front) that decays at one rate for the first 20ms or so, then there's another region that decays more slowly out to about 100 ms, then a third region that decays more slowly still. Likely those are the results of having the ceiling drop down at the rear of the room. That won't be easy to fix. Control rooms should have only one single, smooth, consistent decay rate.

In the mix position my shots show that I have a nice sized dip at about 64-67hz

I'd disagree about that: I'd call it "humongous", instead of "nice sized"...

The upper lows are quite exaggerated listening to mixes.

Correct- Between about 90 Hz and 400 Hz, there's a large boost overall. That might be your speaker settings, or your geometry, or both.

A few feet behind the mix position things sound fairly balanced in the bass range

Correct. Because that's where your head is supposed to be! Closer to 40% of room depth than 25%...

So basically I need help properly locating my mix position and speakers to work with the room better,

First, lets' see some photos of the room, and have some details about your speakers: make, model, and how you have the controls set up. Also, do you have a sub? How are teh speakers mounted? What height? What angle? What locations (with respect to the side and front walls)?

and most likely adding some reflections back in with diffusers

Diffusers don't add reflections: they add diffusion!

You don't want reflections in there (except maybe at very high frequencies), but you very well might need diffusion, and the room is big enough to benefit from it. Diffusers keep energy in the room, preventing it from sounding too dead from over-absorption, and they do so without causing reflections, which is very desirable. Plus, the can be tuned to specific frequency ranges, and they can be oriented in various ways, for various purposes.

and building some tuned resonators, traps, or porous absorbers to fix my 120hz issue in the mix position.

I doubt that would work. The 110 Hz peak is in all of the graphs, taken at various points in the room. That's a huge amount of energy. Pretty hard to absorb. It's going to need some detective work to figure out what that is, but my guess is that it s related to your 0.0.x axials, so probably a very large hard-backed cloud hung at a fairly steep angle would help, as would bass trapping in the horizontal room corners.

And Im really curious as to how to fix the 65hz dip in the mix position.

Firstly by setting up your speaker and listening positions, heights, angles, distances and orientations correctly, then perhaps with treatment.

I know you can tune traps to absorb targeted low frequencies like 65hz but reflecting them back in? Is that even possible?

No, you cannot "reflect" a dip back in again, but you CAN absorb it back in, assuming it is modal (or maybe SBIR). It's simple: what you are seeing as a dip is only because you are looking at a standing wave, and you are located at a point in the room where that wave is at a minimum level. In other words, it is only a dip ath the specific location where you measured it: elsewhere in the room, it is NOT a dip. At the "other end" of the wave, it is at it's peak value. If you put correct absorption at that point, the, the you reduce the energy in the standing wave: you damp it, so to speak. And since it is a standing wave, bringing down the peak automatically "brings up" the null... And it it is a modal issue, since all modes terminate in room corners, the bst place to put the treatment is in the correct corner.

I took several measurements for comparing. Mix Position Speakers L+R, Speaker L, Speaker R, 3' behind the mix position, 6' behind the mix position, and one near each rear corner of the room. If any of those are not necessary I can delete them to shrink the file size. Also please advise me if there are any other specific measurements I should take or if there's any info that I've left out in my wire drawing please let me know.

Next time you run REW tests, please bring your levels up a bit. I know that the REW manual tells you to run tests at 75 dBC, but I prefer to do it at around 85 dBC, to make sure there is a very good signal to noise ratio, and make sure that as many modes as possible are triggered at decent levels.

I'd also like to see a series of measurements taken at 6" intervals, starting a foot in front of your current mix position, and going back to the rear wall. Yes, that will be something like 26 measurements, but it gives a much finer grained picture of the room, so we can figure out what is SBIR, what is modal, what is positional, what is reflections, what is speakers, etc. At each position just do a single test with both speakers.

Also, there's an option in the REW measurement window, called "Start Delay", that sets a pause of several seconds between the time you hit "start" and the time the actual measurement starts. That is to give you enough tome to get out of the room, close the door, and another could of seconds for things to calm down inside. Set that to a long enough pause. That improves the accuracy of the readings, as it ensure that your body is not having any effect on the room.

One other thing: Right now, you are measuring from 1 Hz to 15 kHz in your REW tests. Change that to measure from 15 Hz to 22 kHz: There's no point at all to measuring subsonics, since neither your speakers not your system is capable of doing that, and you can't hear them anyway. And on the high end, it is interesting to see what's happening at the upper limits, even though it won't be accurate.

So let's start with photos of the room, info on your speakers and measurement mic, and that new series of MDAT tests at higher levels.

- Stuart -

booksmart · Post by **booksmart** » Tue Nov 10, 2015 8:30 am

This may be a stupid question, but with his ceiling slope, would he be better off reversing his position in the room? Turn his desk around, move it closer to the South wall?

JasonC · Post by **JasonC** » Wed Nov 11, 2015 3:27 pm

Stuart,
Sorry for the delayed response. I've been out of town
Glad to hear from you again. Thanks for the "tough love". I know I can always count on you in that department. Welp, lets dive in...

What the hell happened???...... how on earth did your control room end up shaped like THAT???!!! Your original plans were nothing at all like that, and neither was your build. What happened? Why did you chop off the front corners of the room, and move your speakers onto the desk? How come you did not soffit mount them? Why is the back of the room lower than the front? Why is the mix position located at the huge modal null point, of 25% of the room depth? Why is your head closer to the speaker than the distance between the speakers? Why are the speaker angles and locations wrong?

Actually the dimensions of the CR are the same as what was originally planned with the exception of the soffits and splayed walls.
I didn't "chop off" the front corners per say, I actually did that with that with the intension of soffit mounting a pair of loudspeakers in the future. Without having the speakers that I intend to use or deciding exactly which ones yet, I couldn't complete a full soffit design with boxes sized to house them so until I acquire said speakers, they are being left as is and waiting to be modified. To be totally frank... Im not soffit mounting a pair of near fields. I understand that that is the method that you prefer but never in my life in all of the studios that I've been in, professionally designed and home studio, have I ever seen a pair of near fields soffit mounted..ever...EVER. I'm not at all trying to say that your method is flawed or incorrect. Im sure it makes the little buggers sound great. But its not for me.
The back of the room is lower than the front because of the A-frame roof trusses on the building. We needed what little space their was on that side of the building for running ducts to the back half of the building. Just one of those things that there was no way around.
25% of the room depth? Im pretty sure that 6'8" isn't 25% of 20', that'd be 5'. Are you going from the point at which the room becomes rectangular? I thought that a mix position should be located within the front 1/3rd of the room?
You are correct, I did have my speaker locations a bit off which I have corrected. The distance between speakers is now equal to the distance to my head. 36".
The speaker angles are 30degrees to the left and right of center aiming just past my ears. Is that not correct? Im using a new desk in this room that is wider than what I was previously using. I think I just set things up too wide at first without realizing it. My fault. Corrected.

The only thing that can be done at this stage is final tweaking, but what I'm seeing in the MDAT file is far beyond the ability of final tweaking.

I remember in my build thread discussing my room layout, dimensions, and geometry with you and you said that my layout was good. Why do you consider it to be terrible now?

What RFZ area? I don't see any RFZ area on your diagram.

Im sorry, guess I used the wrong term. What I meant was that I had absorbers up in the first reflection points on both side walls and a cloud overhead.

...That's why it sounds dead...

Yes you're correct. I knew I had to start out with some basic absorption but I guess I started out with a bit much. I've removed some of the panels from the room and it did increase the decay times some, or at least it sounds like it. Not quite as dead anymore but still kinda dead. Would it be best to remove all panels and start from scratch accept for my clouds and corner traps? It would be a bitch to remove them as the clouds house the lighting for the room and the corner traps are semi permanent, but its doable.

Correct- Between about 90 Hz and 400 Hz, there's a large boost overall. That might be your speaker settings, or your geometry, or both....some details about your speakers: make, model, and how you have the controls set up. Also, do you have a sub? How are teh speakers mounted? What height? What angle? What locations (with respect to the side and front walls)?

My speakers are Dynaudio BM5a's. All the settings (just 3 band eq and low cut) are set to flat. No I don't have a sub. I used to but it gave me a false sense of low end so I stopped using it. I can get the sub that matches the monitors if you think it would help even things out? The speakers are set on top of the racks on my desk sitting on Auralex iso pads. From the floor, the woofers are 4' off the ground and level with my head. No downward or upward angle. The speakers are located 64" in from the side walls and 48" from the front square wall(the 20' point). They are currently 22"(rear of speaker where the port is) from the angled front walls and parallel with them.

Diffusers don't add reflections: they add diffusion! You don't want reflections in there (except maybe at very high frequencies), but you very well might need diffusion, and the room is big enough to benefit from it.

I guess that's what I meant to say. Not so much adding in reflections but scattering them as opposed to absorbing them seeing as how I have the dead factor. I do know that diffusion doesn't help much if its not in the proper location and built for the right frequencies. Thats where I'm lost. Not so much the tuning of the diffusors where to locate them.

No, you cannot "reflect" a dip back in again, but you CAN absorb it back in, assuming it is modal (or maybe SBIR).

I did a few experiments trying to determine if SBIR was responsible for effecting the measurements. I placed a 703 panel on the desk in front of the monitors to catch any reflecting off the desk and it didn't change the response. Actually i think it made it a little worse. I also tried placing a panel on the wall behind the speakers where the energy from the ports were hitting the front wall. No change. I did the same with the panels on the side walls. Still no change. Again, not exactly sure what I'm doing. Is there any other tests or things I can do before doing a measurement to help better detect SBIR?

So let's start with photos of the room, info on your speakers and measurement mic, and that new series of MDAT tests at higher levels.

Here are some photos. I apologize for the grainy iPhone pics but that's all I had on me. Hope I sized them right..

CR-Before Removing Panels.jpg

CR-After removing panels and rearrange.jpg

CR-Clouds.jpg

CR-Left View.jpg

CR-Right.jpg

IMG_3135.jpg

Hope those help and you like the look..

The info on the speakers is listed above. If you need more info let me know or just google Dynaudio BM5a and its all there. The measurement mic is a Presonus PRM1. I couldn't find a calibration file for it online anywhere and it didn't come with one.

I somehow managed to overwrite the file that had all the 20+ measurements on it that I just took that you asked for.

So Im going to retake those now and attach them to the next post shortly so i don't lose all the attachments I just added to this post.
Stand by..........

Jc

JasonC · Post by **JasonC** » Wed Nov 11, 2015 4:05 pm

I forgot to add in my previous post that you'll see in the last picture that I've placed 2" absorbers angled in the upper corners of the front 16' ceiling/wall corners where the ceiling is higher. They aren't super chunks, just a 2" panel on an angle. Bad Idea? Could that be contributing to the loss of low end? I wouldn't think so since the area behind it isn't filled. Thoughts?

Here's the .mdat you requested with the levels up. The first measurement was taken from the center of the mix position at ear level, followed by measurements every 6 inches moving back away from the mix position. I could only get so far without having to take the mic out of that centered and leveled position but I got to within the rear 2 feet of the room. If you need any more measurements or something just isn't right let me know and I'll take more.
You can download the measurements here........ http://we.tl/jXbb8hFObS

Thanks again for the help. Any suggestions or advice is appreciated!

Jc

Soundman2020 · Post by **Soundman2020** » Thu Nov 12, 2015 5:07 pm

Thanks for the "tough love". I know I can always count on you in that department.

My speciality!

I actually did that with that with the intension of soffit mounting a pair of loudspeakers in the future. Without having the speakers that I intend to use or deciding exactly which ones yet, I couldn't complete a full soffit design with boxes sized to house them so until I acquire said speakers, they are being left as is and waiting to be modified.

Yes, but you already set them at an angle of 32°, and made no provision for bass trapping, desk reflections, or ventilation, and it isn't even an RFZ. What happens if it turns out that you need your toe-in angle to be 34°, or 28°, or something else? How are you going to accomplish bass trapping? How are you going to deal with the lobing from the soffits?

Im not soffit mounting a pair of near fields. I understand that that is the method that you prefer but never in my life in all of the studios that I've been in, professionally designed and home studio, have I ever seen a pair of near fields soffit mounted..ever...EVER.

You might want to take a look at some of the places John has designed.. I rather do think his designs can be considered "professional", even if you don't consider mine to be so...

I'd be very interested in your definition of what a "near field" monitor actually is: I don't mean one of the definitions put out by one of the manufacturer's, since those are all wildly different and conflict with each other, but your own definition: How do YOU define what a "near field" monitor is or is not? For example, would you consider a K&H O410 to be near field or far field? What about a Genelec 1032A? Is that a "near" or "far" field monitor? And an Eve SC-408? Or an Adam A77x? Or a Dynaudio BM5A? Or an NS-10? Or an A7X? How do you determine what makes a monitor "near field" or "far field", other than the name the manufacturer prints on the box?

Do yourself a favor, and google "definition of near field monitor", then explain to me how one can determine technically if a monitor is "near field", "mid field", or "far field". I'm really hoping you can do that, because if you can, you'll solve one of the largest mysteries in acoustics, and one that nobody has been able to define so far!

My point is that there is no such thing as a "near field" monitor, since the term "near field" refers to an acoustic condition, not to how a box is made or how drivers are slapped into it. Near field and far field have acoustic meanings, that relate mostly to the room itself, and very little to the monitors. A speaker placed in one room might function as a near-field monitor, but when the exact same speaker is placed in a different room, it might well turn out to be a far-field monitor.

So I'd really be interested in how you will choose your speakers: What technical characteristics of the boxes will allow you to decide that they will act as far-field monitors in your room?

For example, what specific technical characteristic of the Augsurger GA 115 makes it into a "far-field" monitor, that the Genelec 1032A does not have? I'm sitting here looking at the spec sheets of both, and for the life of me I cannot figure out what parameter determines that one of those speakers is a "near field" and the other is not. So please do enlighten me! Should I look at power output? Cone diameter? Directivity index? Frequency response? Peak SPL? THD? Crossover frequency? Input impedance? Group delay? Box dimensions? Intermodulation distortion? I'm having a hard time deciding what parameter I need to look at to determine which is which... And the manufacturer's web sites are no help here, since they disagree with each other on what a near field monitor is! So if even they don't know, how am I supposed to know?

Yes, I'm being a little sarcastic there, but this is one of my pet peeves: these terms have very little meaning when applied to sound sources, since what they actually describe is sound "FIELDS"!!! Ever notice that before? The term itself makes it clear that this isn't about hardware: it is about acoustic fields. They are monitors meant for use in certain "FIELDS". And "fields" are acoustic zones within the room! They are not crossovers, wood types, power amplifiers, or cone materials. They are not even dimensions. Fields are acoustic, not electronic or building materials, or even technical specifications. The "near field" and the "far field" are specific zones in the room that can be measured acoustically, and have specific characteristics that are well defined technically. From the acoustic point of view, if you are listening to ANY speaker while you are seated in the near field zone of the room, then that would make the monitor a "near field" monitor. But if you take a few steps until you are in the acoustic far field of the room, then that would make the speaker into a far-field monitor. See the dilemma?

My guess is that you simply plan to buy a "big" speaker, rather than a "little" one, since you have seen many rooms that you liked with big speakers poking out the front wall. And that's fine! I like big speakers too... when the room can handle them! Otherwise, small speakers make more sense.

Im sure it makes the little buggers sound great.

Who said near-field monitors have to be "little"? Or that far-field monitors have to be "big"? That comment sort of confirms what I suspected: you want big speakers in your room, but don't actually have any technical method for determining if the ones you buy will be "near field" or "far field" (apart form the label on the box, which is basically meaningless).

The back of the room is lower than the front because of the A-frame roof trusses on the building. We needed what little space their was on that side of the building for running ducts to the back half of the building. Just one of those things that there was no way around.

Then that is going to need some major treatment, since it constitutes a compression ceiling...

25% of the room depth? Im pretty sure that 6'8" isn't 25% of 20', that'd be 5'. Are you going from the point at which the room becomes rectangular?

No. I'm going from the approximate average room depth, taking into account the angled front walls. Your room is not rectangular, and does not have six sides. It is trapezoid and has 8 sides. Simple mode calculators and rules of thumb do not apply.

I thought that a mix position should be located within the front 1/3rd of the room?

No. That's the place they should NOT be. Theoretical best location is 38% of room depth. More than about 45 and less than about 30 are really bad. More than 40 and less than 35 are somewhat bad. But once again, that's for rectangular rooms, and is only a starting point anyway. Us designers (professional and non-professional alike) take into account numerous other conditions to determine the best compromise for placing the mix positions, speakers, and treatment.

The speaker angles are 30degrees to the left and right of center aiming just past my ears. Is that not correct?

Depends on the speakers, and the room. For that room, I would probably go a little less than 30°, since it is a long thin room, and the soffits are built incorrectly, taking up a large chunk of the front. I would also go for larger distances: 36" is too close (even for so-called "near-fields"), unless they are very small. Ideally in that room the speakers should be about 70" apart and about 80" from your ears.

Im using a new desk in this room that is wider than what I was previously using.

Even more reason to set the speakers further back, and further apart!

I remember in my build thread discussing my room layout, dimensions, and geometry with you and you said that my layout was good. Why do you consider it to be terrible now?

Mostly because of what you did with the "soffits". But apart from that, here's what I said about your original design:

"Oops! That's a square profile. Your length is almost exactly double your height, so all the modes related to those two axes will line up, just one octave apart (the even harmonics of height will match the odd harmonics of length, all the way up the scale). In general, you should avoid dimensions that are within 5% of being double or triple each other. So your control room fails one of the three critical tests. Fortunately that can be fixed without too much pain, as you only have framing up so far. Not a big deal to move a wall or modify the ceiling."

and also:

"OOOPS! And a big one! To put it bluntly: you have built your control room on top of a very large kick drum"

and

"Then there's a major design issue here!"

plus

" You will have major reflections off the console and desk surface like that, and your soffit faces will look like mangled bat wings. The psycho-acoustics will be big-time problematic: the stereo image will be distorted and frequency-dependent: each instrument will seem to be in a slightly different place, depending on what note it is playing... That's a simple artifact of the way your ear and brain process sound coming in from above instead of from in front. There is no treatment that can fix that."

I hardly think that constitutes saying your design was good.

When I asked which basic room philosophy you intended to follow, you answered "I'm going for RFZ " but you didn't do that. In addition, we discussed the ins and outs of the two main types of soffit design, but you didn't do either of those.

Im sorry, guess I used the wrong term. What I meant was that I had absorbers up in the first reflection points on both side walls and a cloud overhead.

That's standard treatment for ANY room that is NOT RFZ! If you would have built a true RFZ room, there would be no need for treatment on the first reflection points, since there would not be any first reflection points! That's the entire principle of the Reflection Free Zone concept: There are no reflections that reach the ears of the engineer. That's why it is "reflection free". That is accomplished entirely through room geometry, not through treatment. Putting an absorber on the wall does not make a room RFZ...

You originally said that you would do RFZ, but you have not done that, and the results are apparent in the REW data. It might still be possible to fix that, if you really wanted to, by taking apart the soffits and rebuilding them correctly, but my guess is that you will reject that idea.

Yes you're correct. I knew I had to start out with some basic absorption but I guess I started out with a bit much. I've removed some of the panels from the room and it did increase the decay times some, or at least it sounds like it. Not quite as dead anymore but still kinda dead. Would it be best to remove all panels and start from scratch accept for my clouds and corner traps? It would be a bitch to remove them as the clouds house the lighting for the room and the corner traps are semi permanent, but its doable.

There are basically two approaches to tuning a room: One is to design it so that it will be very live, then add treatment to bring the decay times down correctly for each frequency band. The other is to design it so that it will be very dead initially, then add treatment to bring the decay times up correctly for each frequency band. I'm not sure which approach you took, but I suspect it is the former. If you also don't know, and it just sort of happened by accident, then the best idea would be to take out all the treatment that can be taken out easily, and do a REW test like that. If it is still too dead, then the rest will have to come out as well. If you take it all out and the room is STILL too dead, then we'll have to take the opposite approach, but first we'll need to find out WHY it is too dead. That can only be construction materials or construction techniques, since in that size and shape of room it cannot possibly be geometry.

But my guess is that after you take out the easily removable stuff we'll see a decent change. Then we can decide what to do about the stuff that is still in there: It might need modifying.

The speakers are set on top of the racks on my desk

That would explain the dips in the mid-range: almost certainly comb-filtering from the desk surface. It is always a bad idea to have speakers over the desk or on the console meter bridge (despite all those photos of what you see in "professional" studios!).

From the floor, the woofers are 4' off the ground and level with my head.

The acoustic axis should be level with your ears, not the woofers. Check with the manufacturer to find out where the acoustic axis is on your speakers. In most cases it will be close to the tweeter, and on the imaginary line that joins the center of the woofer to the center of the tweeter. If it is too high, then you are not on-axis to the speaker. That' isn't too much of an issue for good speakers, horizontally, but is an issue vertically.

The speakers are located 64" in from the side walls

For that size room, it should be more like 48 to 52 inches from the side walls.

... They are currently 22"(rear of speaker where the port is) from the angled front walls and parallel with them.

Which will produce roughly the following SBIR issues:

Jason-SBIR-2.png

Look familiar?

That's exactly what we are seeing in your REW data. This is very predictable.

Not so much adding in reflections but scattering them

With numeric-sequence diffusers, scattering only happens for about an octave below the actual lowest cut-off frequency. Above that, sound is diffused, not scattered. It's not really the same thing.

I do know that diffusion doesn't help much if its not in the proper location and built for the right frequencies. Thats where I'm lost. Not so much the tuning of the diffusors where to locate them

One basic rule of thumb says that you should have no diffusers within ten feet of your ears: Numeric sequence diffusers create "lobing" patterns in both level and time, as well as frequency and phase. So draw a ten foot radius sphere around your head in SketchUp: that's the limit for where you could locate diffusers in the room. You would also need to tune them such that the wavelength for the lowest cut-off frequency is no longer than one fifth the distance between the diffuser and your ears. And you would also tune them to the frequencies that need it most, according to the REW data.

I did a few experiments trying to determine if SBIR was responsible for effecting the measurements. I placed a 703 panel on the desk in front of the monitors to catch any reflecting off the desk and it didn't change the response.

Was that insulation thick enough to substantially affect the frequency at which the SBIR dip occurred? In other words, if you have a 10 foot wavelength problem, but you are using 1" 703, then obviously you wouldn't see much effect... On the other hand, if you had 8" of 703 and a 4 foot wave problem, then you should indeed see a noticeable effect. According to the predicted SBIR for your speaker under those conditions, the first null would be at about 150 Hz, with a much bigger one at about 300 Hz. We are talking about wavelengths of around 8' and 4' here, so you'd need at least 8" of 703 to have a useful effect. I'd go for 6" of 703 spaced 6" from the wall. That should help quite a bit.

Is there any other tests or things I can do before doing a measurement to help better detect SBIR?

You can do a series of measurements at closely spaced intervals, from your mix positio all the way to the back wall. Every 6" for example.

The patterns you see in that data will tell you which problems are SBIR and which ones are modal.

Here are some photos.. Hope those help and you like the look...

Well, it LOOKS very nice indeed! Excellent workmanship! But the problems are acoustic, not cosmetic...

How was that cloud constructed? Layer by layer, from the cloth on the bottom, all the way up to the empty air above...

CR-Left View.jpg

IS that the final position for the gear rack?

That's a problem. That probably explains some of the symmetry difference, between your left and right speakers. I'd suggest moving it to a position behind you (but we'll have to figure out what that position needs to be: it can't just be any place). Another option would be to build racks under the desk, so you can have your gear there.

Presonus PRM1. I couldn't find a calibration file for it online anywhere and it didn't come with one.

That's fine. They are pretty flat (I have one too), and given the large issues in your room, I doubt that the lack of a calibration file is going to even show up much at all.

They aren't super chunks, just a 2" panel on an angle. Bad Idea?

Probably a good idea, but might need modifying so they don't eat the highs and still do eat the lows better.

Here's the .mdat you requested with the levels up.

Great! I just downloaded that, and I'll take a look in the morning... it's 4:00 am where I am, and I need some shut-eye! I get cranky and sarcastic when I'm over-tired...

(maybe you noticed? )

- Stuart -

JasonC · Post by **JasonC** » Tue Nov 17, 2015 2:58 pm

Stuart,
Thanks for the reply!

What happens if it turns out that you need your toe-in angle to be 34°, or 28°, or something else? How are you going to accomplish bass trapping? How are you going to deal with the lobing from the soffits?

When the time comes to actually put those so-called "soffits" to use

, I knew that I would have to do some serious modifications anyway to properly position the speakers and do traps/porting/power/etc, but without said monitors I was lost at what to do. I should've just left the front corners alone. I was so unsure. I thought constructing the front wall to be very close to whatever it would end up being would help down the road. Looks like I was wrong.

You might want to take a look at some of the places John has designed.. I rather do think his designs can be considered "professional", even if you don't consider mine to be so...

Whoa there buddy, take it easy

! I never at all said I don't consider his or your designs to be professional. I think they're very professional. I don't doubt for a second that those designs work perfectly.

I'd be very interested in your definition of what a "near field" monitor actually is:

I've obviously hit a nerve on this one.

C'mon Stu! You know exactly what I meant but you just chose to go off anyway. I understand that near field and mid field and far field are quite vague nicknames. But I know that you know that you knew exactly what I meant when I said near field. lol

My guess is that you simply plan to buy a "big" speaker, rather than a "little" one, since you have seen many rooms that you liked with big speakers poking out the front wall. And that's fine! I like big speakers too... when the room can handle them! Otherwise, small speakers make more sense.

Exactly. I've always had at least 2 pairs of "little" speakers to mix on that weren't soffit mounted as most people do. Its always worked fine for me in the past so I didn't want to change that. I consider the "big" speakers not to be a necessity and something that would be an addition. I wanted to get into the room with a desk setup to start feeling out the room so I could better chose what would make more sense.

Who said near-field monitors have to be "little"? Or that far-field monitors have to be "big"? That comment sort of confirms what I suspected: you want big speakers in your room, but don't actually have any technical method for determining if the ones you buy will be "near field" or "far field" (apart form the label on the box, which is basically meaningless).

Simple mode calculators and rules of thumb do not apply.

That's been my biggest hang up on this whole project. Not being an acoustician or experienced studio designer I couldn't for the life of me figure out how to determine what the basic responses of a room that wasn't a perfect rectangle would be other than being a total crap shoot. I wish there were some sort of modal calculator or room simulator where you could input a 3D room design and take virtual measurements to help the design.

No. That's the place they should NOT be. Theoretical best location is 38% of room depth….Depends on the speakers, and the room. For that room, I would probably go a little less than 30°, since it is a long thin room, and the soffits are built incorrectly, taking up a large chunk of the front. I would also go for larger distances: 36" is too close (even for so-called "near-fields"), unless they are very small. Ideally in that room the speakers should be about 70" apart and about 80" from your ears. ..

I'm going to build some speaker stands and do some experiments with getting the speakers further from the mix and further apart and try them sitting horizontal as well just to see how things change. I slimmed up the speaker angles and seems like its helped a tad.

You originally said that you would do RFZ, but you have not done that, and the results are apparent in the REW data. It might still be possible to fix that, if you really wanted to, by taking apart the soffits and rebuilding them correctly, but my guess is that you will reject that idea.

I am not against the idea of taking apart the soffits and rebuilding them. Thats why my dumb ass put them there.

I realize that what i did with the front corners was a total gamble and lack of experience. That's what I get for doing this on my own. If ripping out the front corners back down to a rectangle would greatly improve the acoustics in my room, I'm not opposed to it. Is there a way to tell what the differences would be if I were to do so? Like that imaginary simulator I described above? I originally wanted to do an RFZ but I didn't believe I could properly do so within the 14x20 boundaries.

There are basically two approaches to tuning a room: One is to design it so that it will be very live, then add treatment to bring the decay times down correctly for each frequency band. The other is to design it so that it will be very dead initially, then add treatment to bring the decay times up correctly for each frequency band. I'm not sure which approach you took, but I suspect it is the former.

Once I discovered that the dimensions that I was bound by for the control room weren't ideal I thought I would go with the "very dead initially and add decay times back in" approach because I've read of lots of people overcome undesirable dimensions using that technique. I just wasn't sure how far to take it. I've seen places where the entire room is 2 or more inches of 703 and slats and panels used to add decays back in. Planning such a thing was way beyond my comprehension. Would this method be a potential good move for my room and if so where do I start with design and planning? I've messed around with the room simulator in the REW with the wall and ceiling absorptions to try and smooth out the frequency response but I don't know what the values refer to when it says .13 or .41 . How much surface area does that equate to and of what thickness?

How was that cloud constructed? Layer by layer, from the cloth on the bottom, all the way up to the empty air above...

The cloud is very basic. cloth, 2" 703, empty air. It wouldn't be to difficult to modify any of the clouds in the room if it would improve things. They're all constructed the same way.

IS that the final position for the gear rack?

Not exactly. I built those racks myself and they can be easily split into two separate racks and placed individually. But I am going to keep a rack somewhere in that general area to house the patch bay as that is where the live room snakes are coming up through the floor. Not permanent.

Probably a good idea, but might need modifying so they don't eat the highs and still do eat the lows better.

What would be a good mod for them? Some wood slats across the front to reflect?
As I said before I can take out all the wall treatment and start with fresh measurements. I don't want to remove the clouds for testing. I'm willing to take them down for mods if it would help. I do remember just listening to ambient natural sounds of voices and footsteps and such in this room while prepping it before adding treatment and it certainly had some very reflective sound and longer decays. But in your honest opinion would just going for the really dead and then liven it up approach be better in my situation having seen the REWs. It seems like that could give me more control over the correction of the room.

it's 4:00 am where I am, and I need some shut-eye! I get cranky and sarcastic when I'm over-tired... (maybe you noticed? )

Yup. Definitely noticed. You should install an app on your computer that doesn't let you log in to the forum after midnight, but everyone needs a punching bag so I guess I'll be yours.

Gotta get that sleep!
I know my room's not ideal, but its still my room and Im gonna make it work. I really appreciate all your comments and suggestions. Again, I'm always very grateful for any assistance you're willing to give.
Have you had a chance to look at my latest mdat with the multiple measurements you asked for? Do I even wanna know? lol

Thanks again, hope to hear back soon.

Jason

Soundman2020 · Post by **Soundman2020** » Thu Nov 19, 2015 5:25 pm

I should've just left the front corners alone.

That probably would have been better. Right now, it's hard to predict the acoustic response of your room because it is not a simple rectangle, and hard to figure out what is what in the REW data, for the same reason. But it is what it is... As long as you realize that it won't be great until you decide on your final speakers and get them properly soffit mounted, and the associated treatment modification done (if any...), that that's fine. If you just take this is a temporary situation to start with, that will improve at some point down the line, then there's no problem.

I was so unsure

You could have asked!

That's why the forum is here...

I thought constructing the front wall to be very close to whatever it would end up being would help down the road. Looks like I was wrong.

You weren't totally wrong: the problem is that it isn't constructed "very close to what it would end up being". It's vaguely similar, but not anywhere near close enough.

I never at all said I don't consider his or your designs to be professional.

I guess that was a misunderstanding of what you said. When you said "...never in my life in all of the studios that I've been in, professionally designed and home studio, have I ever seen a pair of near fields soffit mounted..ever...EVER." I took that to mean that, by logical deduction, the studios that you have seen with soffit-mounted "near-fields", were not professionally designed. Yet John sometimes uses near-fields in his designs, and so do many other professional studio designers. There are many, many studios that use soffit-mounted "near-fields", so when you said that you had never seen one, I didn't realize that you were just saying that you have not looked at enough studios yet: There's a lot of them out there, even featured in industry magazines (not to mention all over this forum and John's own website). I took that (incorrectly, apparently) as a slight on all the professional studios and home studios that do have soffit-mounted "near-field" speakers. But anyway... water under the bridge. It's now clear that you just want to mount a big speaker in your soffits, not small ones. Did you have anything specific in mind? If it is large, it needs matching to the room, acoustically, as much as possible. Directivity, for example, is important.

I've obviously hit a nerve on this one.

Yup! Misuse of technical terminology for marketing purposes is one of my pet peeves: does it show much?

Yeah, it's not our fault that speaker manufacturers use a term that is basically meaningless to differentiate their products. That's just a shame. It would be nice if manufacturers could all get together one day, and jointly define what they mean when they call a speaker "near-field" or "far-field"... but until then, we'll have to live with the numerous different and contradictory meanings of the term, which only leads to confusion.. and higher sales, I suppose!

But I know that you know that you knew exactly what I meant when I said near field. lol

Yeah, but you also said you've never seen a professionally designed room where one of those is soffit-mounted!

I've always had at least 2 pairs of "little" speakers to mix on that weren't soffit mounted as most people do. Its always worked fine for me in the past so I didn't want to change that.

Yep! I saw that. And once again, that's fine! Many people do mix like that, with small speakers, arranged in ways similar to typical living rooms, to get a feel for how the mix will sound in a typical domestic situation... then they turn on the "real" speakers, in the soffit mounts, to check that the mix will also work for higher-quality situations, and to check details with greater accuracy.... And there's nothing wrong with that workflow! It works. It has for years. Don't get me wrong: I'm not bashing the workflow: I'm bashing the manufacturer's misuse of terms that do have technical meanings, for products where it does not apply...

[RANT MODE = OFF]

I consider the "big" speakers not to be a necessity and something that would be an addition. I wanted to get into the room with a desk setup to start feeling out the room so I could better chose what would make more sense.

It would probably be better to make a list of speakers that you like, then compare their technical specs to your room, and whittle away at the list by eliminating the ones that would not be a good match, acoustically. Then whittle away some more by eliminating the ones outside your budget, and those that cannot be soffit mounted. I reckon you'd find that you end up with a very short list...

It's very important to only look at speakers that match the room. When I design a room for one of my customers, one of the first questions I ask is what main speakers will be used, then I design the room around those speakers, so they work together in harmony, instead of fighting each other. For example, if a speaker has low directivity in the mids, then it will need a larger soffit angle and probably some deeper side-wall treatment. If it is physically a very large speaker, with widely separated drivers, then the distance to the mix position will need to be increased as much as possible. Etc. I'm not much of a fan of the "any speaker works great in any room" club... If the speaker is lousy, it will sound lousy in all rooms: no matter how well you treat the room, it will never sound better than "mediocre" at best. If the room is lousy, then all speakers will sound lousy in it, no matter how good they are. But if the speaker is very good, then it can sound fairly decent even in a mediocre room, and fantastic in a purpose-desinged room.

Not being an acoustician or experienced studio designer I couldn't for the life of me figure out how to determine what the basic responses of a room that wasn't a perfect rectangle would be other than being a total crap shoot.

There are some basic rules-of-thumb and rough estimates that you can do, using boring repetitive procedures and ordinary room-mode calculators. It won't be accurate, but will get you in the ball-park. But the only way to do it accurately is by using FEM/FEA software on a 3D model of your room, in the hands of an operator who understands how to set the boundary conditions correctly, and how to interpret the results correctly. That's too complex and too expensive for the majority of studio builders. And isn't really necessary anyway, unless you have extreme requirements. The actual completed room will very likely not match the predicted outcome all that well anyway, so it's always better to test the room when it is complete (like you did), then decide how to treat it based on that. To my way of thinking, rule-of-thumb prediction and trial-and-error design adjustments will get you a room that is not too bad, and could certainly be better with FEM/FEA, but it will be good enough that you can treat it successfully to get where you want to go.

I wish there were some sort of modal calculator or room simulator where you could input a 3D room design and take virtual measurements to help the design.

Me too! There are a few software products that do that, to a certain extent, but not very accessible and a bit complex to learn and use correctly. They are only really needed for very high end studios where nothing short of perfection is acceptable.

I'm going to build some speaker stands and do some experiments with getting the speakers further from the mix and further apart and try them sitting horizontal as well just to see how things change

I wouldn't bother turning them horizontally: That messes up the psycho-acoustic perception of sound. Our sense of hearing is very accurate horizontally, but not so accurate vertically, which is why most speakers are set up with the tweeter above the woofer: your ears are not very good at noticing that the highs are coming fro a point a bit above where the lows are coming from. Our ears and brains integrate that information, and the sound seems to come from a single point. But turn it sideways, and you have a different situation:: Your brain can now figure out that the woofer and tweeter are not at the same point laterally: Worse still, as you move your head left-and-right, forwards and backwards (which you do all the time while mixing) the relationship of your ears to the positions of the drivers changes: different angles, different intensities: the result is that you lose the precision of the sound-stage, lose clarity, lose definition, gain coloration, etc. The effect is usually subtle... until you move your head... Try it, and listen carefully as you move your head around: you'll see what I mean...

I am not against the idea of taking apart the soffits and rebuilding them.

Great! That's good news. Hopefully it won't be necessary for your little speakers in this temporary situation, but it certainly will be when the time comes to mount your mains, whatever they turn out to be.

Is there a way to tell what the differences would be if I were to do so?

Ball-park? You'd move some of the modes to lower frequencies, which is good. You'd lose some tangential modes and gain back some axial modes, at lower frequencies. The early reflections and SBIR issues from the soffits would disappear, and be replaced by other SBIR issues, at lower frequencies. You'd have the corners for bass trapping. Etc. Overall, there would be an improvement, but the question is if it would be worthwhile or not. And since you do plan to soffit mount something at some point, it probably isn't worth it, at this stage. I would suggest first adjusting the positions and angles as well as possible, and treating as well as possible, then seeing if that is sufficient for what you need in this temporary phase. Only if you can't get acceptable results, then you could consider taking out the soffits and trying again.

I originally wanted to do an RFZ but I didn't believe I could properly do so within the 14x20 boundaries.

John managed to do it inside a shipping container...

OK, he probably didn't nail the full set of RFZ specs in such a small space, but I'm sure he got as close as it is possible to get, given the limitations.

280 square feet is plenty. It's a bit more than the smallest recommended size for a critical listening room. I've done a few rooms that size, and smaller, with no problems. One is under construction right now in Australia (276 square feet), and another currently in the design phase in New Zealand (170 square feet). Once completed last year in LA (220 square feet). It can be done.

I thought I would go with the "very dead initially and add decay times back in" approach because I've read of lots of people overcome undesirable dimensions using that technique. I just wasn't sure how far to take it. I've seen places where the entire room is 2 or more inches of 703 and slats and panels used to add decays back in. Planning such a thing was way beyond my comprehension. Would this method be a potential good move for my room and if so where do I start with design and planning?

You already have hard walls all around the room, so it's probably better to take the other approach: start with an overly live room and damp it down bit by bit, frequency range by frequency range, until i works. Truly dead rooms are usual done with inside-out walls, filled as you say with several inches of porous absorber facing the room, all around. Your walls see, to be built conventionally (drywall facing the room), so you are coming at this from the "live" angle, not the "dead" angle. Bot approaches work: they are just different.

I've messed around with the room simulator in the REW with the wall and ceiling absorptions to try and smooth out the frequency response but I don't know what the values refer to when it says .13 or .41 . How much surface area does that equate to and of what thickness?

That's referring to what portion of the surface is perfect absorption. So 0.5 means that half of the wall is a perfect absorber at all frequencies and all angles (randomly incident sound). The real world doesn't work like that, of course: real panels absorb very differently at different frequencies and different angles, and they don't absorb perfectly anyway. The only thing acts like that in the real works, is a very large hole in the wall, leading to the outdoors on the other side. That's the only thing that absorbs all frequencies perfectly. So this is just a simulation to give you a rough idea of what the response would be... not intended to be an accurate prediction. And of course, it isn't really applicable to your room, which has six walls, not four...

The cloud is very basic. cloth, 2" 703, empty air. It wouldn't be to difficult to modify any of the clouds in the room if it would improve things. They're all constructed the same way.

I'd suggest putting a hard "back" on the clouds: Maybe 3/4" MDF or plywood, making it 4" of 703 below and 2" above, and putting a thin plastic membrane between the 703 on the bottom and the fabric finish. Hang it from chains (it will be heavy) and angle it about 20° (lower over the speakers, higher over the desk): Do the big one in the middle first, as a "proof of concept" if you want, to see how it works. Do a REW test right before you take it down and another right after you put up the modified version. You should see the vertical modes more diffuse and better damped, the ceiling reflections should disappear, and the overall decay time should come down a bit in the lows and mids, with the highs not being affected too much.

Not exactly. I built those racks myself and they can be easily split into two separate racks and placed individually.

I'd suggest putting them under the desk, on either side of your legs. Either that, or behind your chair, but carefully positions so that they don't cause reflections to your ears.

What would be a good mod for them? Some wood slats across the front to reflect?

Perhaps, but I'd start out by putting thick-ish plastic across the front, (between the 703 and the fabric). If that doesn't do the trick, the strategically placed slats would also help. As long as the don't cause spectral reflections back to the mix position. You might even want to consider geometric diffusers in front of the bass traps. And more absorption inside.

As I said before I can take out all the wall treatment and start with fresh measurements.

Yes, that is worth doing. Try to get the speakers, desk, and listening position as close as possible to the "standard" configuration, then do one set of REW tests with the room as empty as possible of acoustic treatment (including you! Run the tests with the delay on, so you can get out of the room and shut the door before the test runs) then do a second set with the treatment in. You could even do several tests, after you put in each piece of treatment so you can see which treatment is affecting which acoustic parameters.

By "set of tests" I mean one with just the left speaker, one with just the right speaker, and one with both. Do that set of three each time.

I do remember just listening to ambient natural sounds of voices and footsteps and such in this room while prepping it before adding treatment and it certainly had some very reflective sound and longer decays.

Yep! That's what we want to see in your "baseline" test; the room in its barest, empty state, with no treatment (or as little as possible). That will show some really ugly graphs, which is great! That tells you exactly how the untamed room is behaving. Then you can see what changes with each round of treatment you put in, so it becomes clear what is not working, what is working, and how each piece affects the overall response. That "baseline" set of tests is very important, as it gives you a point of reference for everything that comes afterwards.

But in your honest opinion would just going for the really dead and then liven it up approach be better in my situation having seen the REWs.

I don't think it is worth it. Your walls area already up, they are built conventionally, and covering the, all in 6" of 703 would be expensive, overkill, and it would take a foot off the room in each dimension. If you empty the room as much as possible, taking it back to "bare bones" then hopefully we'll see some very long decay times across the board, uneven response in both time and frequency and lots of reflections. If we get that, the that's fine: we can start taming those, one by one, until either you are happy with the result, or you run out of money...

Yup. Definitely noticed. You should install an app on your computer that doesn't let you log in to the forum after midnight,

Dang! I did it again! I came to your thread after midnight, and it's past 4 am again!

but everyone needs a punching bag so I guess I'll be yours.

Hey! No favoritism! Why should you get all the special treatment?

I know my room's not ideal, but its still my room and Im gonna make it work.

We can make it work, I'm sure. But there's gonna be a lot of work in there, if you really want to get it great and still keep those soffit thingies! And also a lot of work if you decide to go the other way: choose the final main speakers now, then re-build the soffits for them now, even if you don't buy them yet. You could make your room into a good semblance of RFZ like that, and avoid re-building the soffits later. Just leave the empty space to insert the speakers later, with a thick wooden front over it for now. That might be worth the effort, if you can decide on your final speakers.

I really appreciate all your comments and suggestions. Again, I'm always very grateful for any assistance you're willing to give.

- Stuart -

JasonC · Post by **JasonC** » Fri Nov 20, 2015 8:23 am

Thanks for getting back so quickly...lots of good info.

So here's where Im at. I'm just not ready to chose my speakers at this point. I've gotta do like you said and pick the correct speakers for the room and it is a lengthy, tedious process and one that's not what I consider a die hard necessity seeing as how I don't "need" them per say. I'm not opposed demo'ing the front corners but I'd only want to do so if I was pretty darn certain that it would be a great improvement. I know that's a backwards. Without having the speakers to properly design a soffit I should've just left the corners alone. Removing them now would be quite a task which I'd like to avoid if possible so I'd like to start by trying to fix things as best I can via treatment first before having to do some serious demolition. I would greatly appreciate your help in the method and process. I'm going to start by removing all absorption aside from the clouds and two corner traps, couch, rugs, and do some tests after trying to get my desk and speaker locations worked out. Based on the room's shape I know that there are ideal locations to place absorbers where they will work better for standing waves,etc. I know I've seen on calculators where it shows where problems occur in relation to the room depth. Is this where I should be placing my absorber panels on the side walls?

Theoretical best location is 38% of room depth..... I would also go for larger distances: 36" is too close (even for so-called "near-fields"), unless they are very small. Ideally in that room the speakers should be about 70" apart and about 80" from your ears.

Just to be clear when you say 38% of room depth you mean my ears should be 38% of room depth, correct? Using that percentage where should my speakers be in relation to the front wall? Should they be as close to the front walls as possible leaving some room for the 6" absorbers you described to be hung off the wall for help with SBIR? I'm guessing I'll just have to play with it. 70" apart and 80" from my ears? The 80" makes sense but the 70" seems a little wide spread. But thinking about it now sitting at the desk, 80" is almost exactly where my mix position is from the front splayed walls. Kinda relates to my previous question about mix position vs. speaker distance from front wall. It also makes the 70" width make more sense. If it'd be ideal to have them located very close to the front wall like that I'd almost be inclined just to cut into the front walls and soffit mount them. Hmmm.
Depending on the results of the moving around and test data I may also remove the cloud over the mix position to modify it in the way that you described. Would plastic sheeting work for that liner between the fabric and 703? Being a hard backed cloud, does it have to be sealed like a resonator would? The reason I ask is because of light fixtures that are in the clouds. They are slightly taller than where the hard back would be screwed and glued to the frame. Also, it brings up a heat issue. The fixtures have to have some room to breathe. It wouldn't be hard to boar some holes in the backer to allow the fixtures to be unobstructed and breathe. If having a few 4" holes around the outer edges of the back is okay it would be an easy mod. If its gotta be solid than I'd have to really get crazy with it.

John managed to do it inside a shipping container... OK, he probably didn't nail the full set of RFZ specs in such a small space, but I'm sure he got as close as it is possible to get, given the limitations.

Funny you say that. I know a guy here who has his CR set up in a shipping container and his little room and mixes sound excellent! If he can make it work, so can I.

With my room the way it is is it possible for me to get my room close to RFZ without any major construction or demo? Just exploring options..

If you empty the room as much as possible, taking it back to "bare bones" then hopefully we'll see some very long decay times across the board, uneven response in both time and frequency and lots of reflections. If we get that, the that's fine: we can start taming those, one by one, until either you are happy with the result, or you run out of money...

Hell Yes! Lets do it!

So I'll start by stripping the room as best as possible and begin testing but I want to hear back from you about that speaker placement thing first so that I'm starting in the right place. And i need someone to help me move the couch. lol.

We can make it work, I'm sure. But there's gonna be a lot of work in there,

Now that's the kind of positive criticism I need Stu!! Gives me hope. Seeing as how this is going to be my nest for the distant future I'm willing to do everything possible to get it as ideal as I can.
Thanks again and I'll get on the tests asap!

Jason

JasonC · Post by **JasonC** » Fri Nov 20, 2015 11:25 am

I jumped right in after my last post and started moving my speakers around. Took them off the desk and laid them out like you suggested 70" apart. I placed them directly in front of the front splayed walls. Maybe 4" from wall to rear of speaker.

speakers relocated.JPG

Threw on some music and right away noticed a big difference in the response. In a Good Way! The bass response is a good bit smoother. I took room measurements starting at mix position being 60" from the speaker faces and then moved back in 6" increments to 82" to play with that 30-40% room depth factor. The new measurements reveal a smoother response at 110ish hertz where that giant mountain of energy was before moving things. Its still there but drastically reduced. And the giant dip at 65z has moved a bit. Now its around 70-80hz and not quite as drastic. I also did some left and right speaker measurements. Correct me if I'm wrong.. When looking for SBIR, if I take a measurement with the mic centered of just the left and then just the right and lay the graphs over each other, any major differences would indicate SBIR or some other reflective flaw...Right? When I did that I noticed that the left side had a different response in a certain small bandwidth than the right. Makes me think it could've been caused by reflections off of the rack which is on my right side. I also know that the desk is most likely causing some SBIR issues. Just in listening to music in here now I can tell a pretty good improvement on the overall sound of the room in several locations. Thanks for the tip!

After removing all the 703 from the side walls the room livened up a pretty good deal as well. I believe this is a good starting point to move forward with treating.
I'll do another round of 6" increment tests from mix position to back wall and upload them. Hopefully later tonight.

Thanks

Jc

Soundman2020 · Post by **Soundman2020** » Fri Nov 20, 2015 11:32 am

Based on the room's shape I know that there are ideal locations to place absorbers where they will work better for standing waves,etc. I know I've seen on calculators where it shows where problems occur in relation to the room depth. Is this where I should be placing my absorber panels on the side walls?

All room modes terminate in corners, so that's the most effective way of hitting them. You also get a boost in trapping effectiveness: If you put deep traps in the corner between two walls, for example, then you are hitting all the modes associated with BOTH of those walls. If you put the treatment in the middle of the wall, you only hit the mode associated with that wall. And if you put trapping in a "tri-corner" (where two walls and the ceiling meet, or two walls and the floor) then you are hitting all modes in all directions at once.

You can see this on Andy's room mode calculator, which has a really nice 3D diagram that shows where the peaks and nulls for each mode are:

http://amroc.andymel.eu/

Just put in any old dimensions to get an idea: I just tried 456 cm L, 345 W and 234 H. Then run your mouse cursor over the individual mode lines on the horizontal chart, and watch the 3D representation: You will see that each and every mode, in all directions, has a node in all eight corners of the room. So corners is where you want as much bass trapping as possible, since you are guaranteed to hit them all.

However, trapping does have to be thick: absorption works on the velocity component of the wave, not the pressure component, and up against the wall the velocity is obviously zero while the pressure is peaking. It's only when you get several cm away from the wall that you have some velocity and less pressure, and that's where absorption starts to be effective. Hence, suprchunks stick out a couple of feet, and so do hangers. They need to, in order to be certain of being located where there is useful velocity.

Just to be clear when you say 38% of room depth you mean my ears should be 38% of room depth,

Correct, but that isn't written in stone! Especially for non-rectangular rooms. It's a good starting point, but not necessarily the best in all cases, since rooms aren't perfectly shaped, and are not made of perfect materials, and speakers are not perfect either.

You can clearly see this 38% effect by playing around with Room Sim in REW. Set up a couple of speakers close to the front wall at 1.2m above the floor, 28% from each side wall, put your head on the room center-line, also at 1.2m above the floor, then move your head forwards and backwards while watching the graph. When you get to around 38% of room depth, you'll see that the graphs is the best compromise. Still not very good, but better than the bad locations. Try, for example, 25% and 50%...

Using that percentage where should my speakers be in relation to the front wall? Should they be as close to the front walls as possible leaving some room for the 6" absorbers you described to be hung off the wall for help with SBIR?

Theoretically, yes... for a rectangular room! If you have a very large room, then the best place for killing SBIR is to have your speakers a couple of meters away from all walls, or at least more than 1.5m. That forces all SBIR problems down out of the audible spectrum. But with a small room, you can't do that, for obvious reasons. So the next best thing is to jam them tight up against the front wall, which pushes the SBIR artifacts up into the mid range, where they are less objectionable. Of course, the best place of all is to mount your speakers in the wall, flush with the surface: that way, there are no SBIR artifacts... none at all. Not even one. That's one of the many reasons why soffit mounting is so desirable. SBIR ceases to exist.

However, since your speakers are not soffit mounted, and the room is not rectangular, there might be other stuff going on at certain points in the room that could interact with the SBIR effects, so you might need to nudge and tweak to find the best location REW is very useful for that.

70" apart and 80" from my ears? The 80" makes sense but the 70" seems a little wide spread.

The general "rule" is that the speakers should be about as far apart as they are from your head, roughly, in order to get a good stereo image and clear, accurate sound stage. If you go too much wider than that, you spread the sound stage too much and the sweet-spot, and if you go too narrow then you compress the sound stage and sweet-spot.

But thinking about it now sitting at the desk, 80" is almost exactly where my mix position is from the front splayed walls.

That would make sense, and would fit in well with the aprox. 30° angle that we need. You might be able to go a couple of inches further forward, so you'd be closer to the speakers and we could bring them a bit closer together, but then you start getting into other issues. Pretty much everything about studio design is compromise: you can never do everything perfectly, because the "perfect" position or angle for one parameter normally ends up being a really bad position or angle for a different parameter. So you are forced to trade off one against the other, decide which is more important and give it greater priority, etc. That 70" / 80" / <30° setup I described is a bunch of compromises that should work reasonably well for your situation. You can slide them around a bit to see if there might be a better compromise close by, but don't stray too far, or you'll be compromising something else that you might not have considered. For example, you might find a place that has flatter frequency response when you analyze it with REW, but then when you actually listen there, you'll notice that the sound-stage is "flat", or there's a problem with directionality. Etc.

If it'd be ideal to have them located very close to the front wall like that I'd almost be inclined just to cut into the front walls and soffit mount them. Hmmm.

Ain't it amazing how things work out?

That said, soffit-mounting is a bit more complex than just cutting a hole in the wall and poking the speaker through... That's the concept, yes, but reality strikes, and it turns out that you need to consider things such as lobing, focusing, power balance, baffle step response, mass, rigidity, and even simply how the hell to mount them damn thing so it stays in place!

Depending on the results of the moving around and test data I may also remove the cloud over the mix position to modify it in the way that you described.

The hard backing helps to diffuse or break up the vertical modes, to a certain extent, and also helps with first order reflections off the ceiling, so it needs to be angled correctly. It also helps with overall absorption.

Would plastic sheeting work for that liner between the fabric and 703?

Yes. The plastic has two main purposes. One is to prevent fibers from filtering out of the insulation over time, and messing up your gear, while the other is to prevent it from sucking up too much of the high end, so you don't end up with a room that sounds dull, muddy, and lifeless. The thickness of the plastic can be selected to "tune" that, such that the plastic reflects sounds above a certain frequency, while allowing through lower frequencies.

Being a hard backed cloud, does it have to be sealed like a resonator would?

No, not necessary. It is not tuned nor resonant, so sealing isn't needed.

The reason I ask is because of light fixtures that are in the clouds. They are slightly taller than where the hard back would be screwed and glued to the frame.

No problem. You can have as many holes as you want in the hard back (within reason!).

Also, it brings up a heat issue. The fixtures have to have some room to breathe. It wouldn't be hard to boar some holes in the backer to allow the fixtures to be unobstructed and breathe.

No problem there either. The cloud is not critical at all in that aspect. Leave a decent size gap, and whatever ventilation you need. It won't harm the acoustics, and might even help due to some limited diffusion going on around all those holes, light cans, and things.

If having a few 4" holes around the outer edges of the back is okay it would be an easy mod. If its gotta be solid than I'd have to really get crazy with it.

No problem.

With my room the way it is is it possible for me to get my room close to RFZ without any major construction or demo?

Apart from taking out the soffits and re-building them, then treating the room properly, there's no other major construction involved. No modifications to walls, floor, ceiling, etc. The soffit and treatment is pretty much all you need to do to establish a good RFZ. But here too, it needs to be done with care: properly designed, carefully checked, properly built, accurate dimensions...

So I'll start by stripping the room as best as possible and begin testing but I want to hear back from you about that speaker placement thing first so that I'm starting in the right place.

I sounds like a good plan! I think I covered that above.

What you could also do, if you really want to get fancy, is a series of other tests, simulating slightly different scenarios, such as moving the mic 6" forwards and re-aiming the speakers as though your head was there, and do a REW test, then in that same position sliding he speakers 6" further out and 6" further in with more REW tests. then repeating that 6" behind the original position with yet more REW tests. That will give us more data to look at, and figure out if there might be a better geometry layout.

And i need someone to help me move the couch.

Cool! Send my plane ticket, and I'll be happy to help you move the couch!

Thanks again and I'll get on the tests asap!

One other thing: take pictures of each test situation, showing where the mic and speakers are, so you have a reference, and label each of your REW tests with all pertinent details, so we know how to get back to that situation if one looks really good. Also, run all of the REW tests with even you out of the room! I think I already mentioned that. Set the timer so that you have plenty of time to get out of the room, close the door, and wait for things to calm down again inside before the test starts running.

- Stuart -

Soundman2020 · Post by **Soundman2020** » Fri Nov 20, 2015 1:25 pm

I posted the above before I saw your new post!

started moving my speakers around. Took them off the desk and laid them out like you suggested 70" apart. I placed them directly in front of the front splayed walls. Maybe 4" from wall to rear of speaker. ... Threw on some music and right away noticed a big difference in the response. In a Good Way! The bass response is a good bit smoother.

Don't you just love it when you do something in practice that was predicted by theory and empirical experience, and it works out? What you describe is what I expected. (I'm trying real hard not to say "I told you so!"

)

Correct me if I'm wrong.. When looking for SBIR, if I take a measurement with the mic centered of just the left and then just the right and lay the graphs over each other, any major differences would indicate SBIR or some other reflective flaw...Right?

Not necessarily: SBIR relates to the relationship between the speaker and nearby walls or other boundaries (hence the name), and is not at all related to room dimensions, but modes relate to standing waves in the room which depend entirely on room dimensions but are independent of the speaker location. So the best way of identifying SBIR as opposed to modal issues is to look at the REW data from several mic positions. You'll be looking at a different set of modes for each mic location, but the same SBIR everywhere, so you look for dips and peaks that do NOT change with mic location: those are likely SBIR. Also, modal peaks "ring": they decay over time, since they are standing waves with "stored" energy that dissipates slowly once the trigger signal is removed, but SBIR is not standing waves, so it dies away at the same rate as the diffuse field.

In other words, modal peaks ring and die slowly, and will be at different frequencies for different points in the room. SBIR peaks don't ring, do die fast, and will be at the same frequency for all points in the room. Those are your big clues. But for both cases, do tests with just one speaker at a time turned on, not both at once, or you might be looking at interference issues between speakers rather than true SBIR issues.

But do be careful here: just because you found a peak that dies fast and doesn't change with mic location, does not prove that it really is SBIR. It could be other things too, such as "lobing" or focusing effects from a speaker, or it could be comb filtering, or even some type of impedance effect, cause by the mismatch in impedance between the speaker drivers and the room acoustic load. If you want higher certainty that a peak or null is SBIR, then move the speaker axially towards the mic but don't change anything else. In other words, do a REW test, move the speaker directly towards the mic a few inches, do another test, move the speaker again, directly towards the mic, do another test: If the peak you were looking at really is SBIR, it will move to a different frequency for each speaker location. Modal peaks might be higher or lower when you do that, since the speaker might trigger them to a greater or lesser extent, and they might ring for a longer or lesser time, but they wont change frequency, because your mic is at a fixed point in the room: it sees only one set of modes a that point, and they won't change since the mic did not change relative to the walls, floor or ceiling. If something changes to a different frequency with this test, then it is pretty much sure to be SBIR.

By the same token, just because you found a peak that rings long and dies slowly does not mean for sure that it is modal: it could be something in the room resonating at it's natural frequency, such as a raised floor for example, or an undamped soffit cavity, or part of the desk or rack, or perhaps even a wall or ceiling panel that was not attached properly, or something in the cloud... lots of things that are not a mode can resonate and look like one.

In other words, don't jump to conclusions: acoustics isn't always intuitive, and there are many, many things that could fool you into thinking something is a mode when it isn't, or fool you into thinking that something is not SBIR when it is. Or vice versa.

When I did that I noticed that the left side had a different response in a certain small bandwidth than the right. Makes me think it could've been caused by reflections off of the rack which is on my right side.

Very probable. That's why I suggested splitting your rack gear symmetrically around you, under the desk (best possible location) or placing it symmetrically behind you (not so good, as it can cause reflections to your ears within the Haas time, and spectral, not diffuse).

I also know that the desk is most likely causing some SBIR issues.

Actually the desk won't be doing that: but it will be causing a mid-range peak plus comb-filtering artifacts, and also possibly early reflection. There are things you can do inside REW to help identify that, such as windowing the impulse responses.

Just in listening to music in here now I can tell a pretty good improvement on the overall sound of the room in several locations. Thanks for the tip!

That's what we are hear for! I don't like to beat my own drum, since it sounds like boasting or immodesty, when that isn't the intention at all, but I'm glad you found out that I do know what I'm talking about, at least a little bit...

It's always nice when people implement what we suggest, and see that it actually does work. That comment comes a lot more from frustration than it does from pride: too often I suggest things that people should do, but they don't do it and then they carry on asking for more advice, or argue as to why what I said won't work! That always leaves me thinking: SPAM FOR OUTRAGEOUSLY TERRIBLE SHOES BLOCKED! Just do it! Why not just try it! I KNOW it will work. And if it doesn't, then I'll help figure out why, and I'll learn something new as well, which is always great.

[RANT MODE = OFF]

So it's great that the suggestions worked for you, and you have a good starting point to tweak the geometry, do the baseline tests, then start putting the treatment you need in the places that need it.

After removing all the 703 from the side walls the room livened up a pretty good deal as well. I believe this is a good starting point to move forward with treating.

Do you have a REW test that you did after getting all that out? It doesn't matter which one, or mic locations: I'd just like to take a look at a couple of things, to make sure that you really do have good starting point for the baseline test. Upload whatever you have, before rushing into the more detailed stuff.

One thing I did notice: Is that carpet on your floor? Or is it something else? Ceramic tile maybe? Please tell me it isn't carpet.... Please... Although it does look a lot like it...

- Stuart -

JasonC · Post by **JasonC** » Fri Nov 20, 2015 4:51 pm

Don't you just love it when you do something in practice that was predicted by theory and empirical experience, and it works out? What you describe is what I expected. (I'm trying real hard not to say "I told you so!" )

Permission Granted.

That's what we are hear for! I don't like to beat my own drum, since it sounds like boasting or immodesty, when that isn't the intention at all, but I'm glad you found out that I do know what I'm talking about, at least a little bit..

Believe me... If it weren't for your advice on my build thread and researching other builds and posts on this forum...I'd be in a very dark place right now. Like everyone on this site knows and respects... if your going to build a recording studio you have to be at least 75% crazy. And the fact that acoustics in general is at least 75% crazy.... we're talkin' 150% crazy. .. Thats a lotta crazy. Getting the experienced advice from someone thats done all kinds of crazy is invaluable.
Thank You.

That said, soffit-mounting is a bit more complex than just cutting a hole in the wall and poking the speaker through... That's the concept, yes, but reality strikes, and it turns out that you need to consider things such as lobing, focusing, power balance, baffle step response, mass, rigidity, and even simply how the hell to mount them damn thing so it stays in place!

Precisely why I didn't want to take it any further than I did. Way to much stuff that has to be designed around the specific cabinet. The front splayed walls are the size that they are so that I'd have room (enough depth and width left to right) to house different sized cabinets so I'd have options down the road and be able to better tweak the position. I really just wanted to get a frame up that I could build in to.

The hard backing helps to diffuse or break up the vertical modes, to a certain extent, and also helps with first order reflections off the ceiling, so it needs to be angled correctly. It also helps with overall absorption.

Copy that.

Yes. The plastic has two main purposes. One is to prevent fibers from filtering out of the insulation over time, and messing up your gear, while the other is to prevent it from sucking up too much of the high end, so you don't end up with a room that sounds dull, muddy, and lifeless. The thickness of the plastic can be selected to "tune" that, such that the plastic reflects sounds above a certain frequency, while allowing through lower frequencies.

Copy that.
I could easily modify all of the panels and clouds in this room, or at least whats needed, in no time. Let me ask you this.. I've read where lots of people will mount general store "peg board" (the perforated fiber board you'd use for a tool rack) to the front of their 703 panels. A porous membrane absorber, right? They say using pegboard smoothes out the high range absorption. I know that the hole sizes in the pegboard "tune" the panel or enclosure in the same sort of way as a slot resonator using circles instead of slots. I had thought of using this method of cutting certain sized holes into hard faced panels to help tune while providing some broadband absorption but I didn't get very far because I couldn't find reliable info. Care to weigh in?

One other thing: take pictures of each test situation, showing where the mic and speakers are, so you have a reference, and label each of your REW tests with all pertinent details, so we know how to get back to that situation if one looks really good. Also, run all of the REW tests with even you out of the room! I think I already mentioned that. Set the timer so that you have plenty of time to get out of the room, close the door, and wait for things to calm down again inside before the test starts running.

Gotcha. On my last test I put more info in the test description for each test. From the point of view of someone who knows the program, whats the best way to label the data so it makes it easier to understand? Is there any other than a title and description? I've been setting the pre delay on my measurements so that I have time to get out and close the door. I'll add a few seconds for the hell of it.
Thanks again for all the advice and criticism. I'm gonna gather some more data and post tomorrow and we can start sorting things out.

I'm psyched!

Jc

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