Control Room Acoustics

[johnlee]

This is my first post on any forum. I've very much appreciated this forum as an extremely useful resource.

I've built/building a recording studio in 2 stages. Stage 1 being a control room in which I record and mix. Stage 2 involves a live room, amp room and vocal booth.

Control room dimensions are 4.8m(W) x 7m(L) x 3m (H) (I've included a SketchUp of the room with more details)

I'm hoping someone can suggest acoustic treatment and monitor placement in my control room. I've been using the room for the past few months with some simple baffles on the ceiling and walls (I've been experimenting with placement). Basically I am very happy with the rooms acoustics but as expected it does have a lumpy response under 250Hz (problem peak frequencies seem to be 48, 109, 144 approx and a trough at 57Hz approx- determined by listening to an oscillator).

I'm interested in starting the acoustic treatment from scratch to achieve optimum performance.

You will notice in the SketchUp that I have oriented the room so that I am looking out the outside window. I realise this is perhaps not ideal but it is an important lifestyle and aesthetic decision for me. I wanted natural light, to see the outside world, prevent glare on computer monitors and to avoid watching the live room unless required, and listen more. I'm also happy to cover some of this outside windows edge with a corner baffle if required. (this windows position and size was determined by an existing window). I also like working in rooms orientated longways.

I should also mention that I don't really understand the calculators and some of the technical information of this topic.

Thank you in advance for your assistance.

John

[Soundman2020]

Hi John, and welcome to the forum! But please check the rules for posting: you seem to be missing something important...

I'm hoping someone can suggest acoustic treatment and monitor placement in my control room.

The general suggestion for monitor placement is to mount them in soffits if you want the very best sound possible, or as second choice to put them on very massive, heavy, rigid stands with a decoupling layer right under the speaker (some type of resilient rubber, where type and size depends on your speakers), on top of the stand. Some people use concrete blocks stacked up for their stands, others use hollow metal or PVC stands and fill them with dry sand, to get the mass that you need. Either method works. Wrap attractive cloth around the stands to hide the "ugly" factor. The reason for this is to prevent the speakers transmitting sound into the floor, and thus muddying up the room, acoustically. The mass resits movement, and the rubber isolates (decouples) and also damps. The concept is that you want the speakers to behave as if they were not attached to the room at all, and were just sort of floating in space. That way, you only get the direct sound hitting your ears, instead of sound that has followed other paths around the room and therefore arrives either before or after the direct sound.

The speakers themselves should be placed at a height of 1.2m above the floor (which is ear-height when seated for most people), but that refers to the height of the acoustic axis of the speakers, not the top or bottom of the speaker cabinet. Some manufacturers publish the location of the axis in their documentation, others don't. It will be on an imaginary line between the center of the woofer and the center of the tweeter, very much closer to the tweeter: Some folks even suggest just using the center of the tweeter, but that's not 100% accurate. That axis will point out from that location, straight forward, at an angle of 90° to the surface of the front panel. In other words, it will be "normal" to the panel. That axis is important for correct placement, so try to figure out where it is on your speakers.

The speakers should be positioned about 2 m apart and angled inwards at about 30°, such that the intersection of those imaginary acoustic axes falls a few inches behind your head when you are seated. That will put your head and each of the speakers at the apexes of a triangle. In turn, your head should be located at roughly 38% of the room depth (distance from front wall to back wall), and on the room center line. The room must be symmetrical about that center line (left right).

OK, that's the general guideline, but that's the key word: "guideline"! Start from that setup, then move things a bit at a time and see if you can get better sound. In particular, the "38%" rule is not a rule: it's just a good starting point, a the theoretically best location in the room, that suffers the least from modal nulls and peaks. But that's theory, and reality might not match, so play around: move your chair a few inches back and forward, re-angling the speakers each time to get that intersect a few inches behind your head, and see if there is a better location (once again, 30° is the theoretical optimum angle, but you won't get arrested by the Studio Monitor Police if you end up at 28°, or 34°, or whatever). You can also play a bit with speaker separation: move them a bit further apart, and a bit closer together (re-angling, of course), and see if that improves things any. Bare in mind that as you increase the angle and/or move them further apart, you'll be broadening the stereo image and sound stage, but squashing up the sweet spot. A broader sound stage is not a bad thing, as it can give you more detail in placing instruments in space while mixing, but you should be aware that your setup does have a broader stage. The "squashed" sweet spot might be an issue if you like to move around a lot as you mix, since you might be getting your head away from it.

Once you have your speakers and head in the place that sounds best in the room, then you can refine the acoustic treatment. Before setting up the speakers you should at least have the typical basic treatment setup in place already: large bass traps in the corners, and thick absorption on all first reflection points as well as across the rear wall. But once you have the geometry refined, then you should actually measure the acoustic response of your room, using something like REW ("Room EQ Wizard"). Testing with tones like you did can give you a rough idea of where some of the issues are, but it won't tell you everything: There's no substitute for running a full suite of tests with REW. It will expose all of the problems, and will help identify what each of them is due to, as well as suggesting ways to deal with them. So download REW (It's FREE!!!! ) ), set up a mic with flat response in your listening position, and let REW do it's thing through each speaker individually, one at a time. Post your graphs here so we can help figure out what is going on. Also, carefully measure the exact position of the mic, since you will need to get it back to that exact same position each time you repeat the test in the future, with different treatment. The mic must be back in the precise same position for each test, accurate to within a few mm in all three axes. If not, then you cannot compare against the previous graphs, and you'll never know what each stage of treatment accomplished, or what to do next. This is a VERY important point!

Control room dimensions are 4.8m(W) x 7m(L) x 3m (H)

With those dimensions, you are practically spot on for one of Sepmeyer's best ratios (his third best, actually). It passes all three of the BBC's critical tests, the volume of the room is very good (it's a nice size), but it doesn't have an entirely even modal spread in the low end.

problem peak frequencies seem to be 48, 109, 144 approx and a trough at 57Hz approx-

49 is your 2,0,0 axial mode, so that makes sense: Rear wall absorption might help with that.
109 is your 0,3,0 axial mode, so that makes sense too. Maybe slot walls on the sides would help there (especially if you splay them just a bit).
143.5 is your 0,4,0 axial, which is the exact same problem as above, but the next harmonic up. Same solution. There's probably another one around 72 Hz, and the big fundamental for all of them around 36 Hz, but maybe your speakers don't go low enough for you to hear that, and in any case you have two modes right on top of each other at 72 and 73, which might be interacting somehow.

The 57 Hz dip matches your 0,0,1 axial at 57.4, so that's also not surprising. For that one, probably a hard-backed, angled cloud would help a lot.

So overall you are hearing big issue with your major axial modes, which to me implies that you don't have any bass trapping in that room! Or if you do have some, then it is nowhere hear enough. So I'd start by looking into that, and loading up the room corners with large, deep bass traps, covered with thin membranes to not suck out too much of the highs.

You will notice in the SketchUp that I have oriented the room so that I am looking out the outside window. I realise this is perhaps not ideal but it is an important lifestyle and aesthetic decision for me.

It's not too much of a problem, but it does mean that it will be difficult to treat that room so it sounds good. You are going to have to make a choice between the view and the acoustics, to a certain extent. To get the room sound as good as it possibly can, you would need to narrow that window a bit such that you can either mount your speakers properly in soffits, or if you go with second-best (on heavy stands) then you'll still need to put thick absorption behind the speakers, plus bass traps in the corners. So if you would be prepared to sacrifice about a meter of the right edge of that window, then you could drastically improve the sound. Without that, there's no way you can make it sound good. SBIR and lack of symmetry would be too much of an issue.

I also like working in rooms orientated longways.

Great! that's the best way to work! It puts the largest possible distance between you and the back wall, which means that the reflections coming of the rear wall take longer to get back to you. That's one of the concepts of studio design: you should not be able to hear any reflections until at least 20 ms after the direct sound reaches your ears from the speakers, and even then the level of the reflection should be 20 dB down, as compared to the direct sound. A large room oriented lengthways, like yours, makes that a lot easier to achieve.

I should also mention that I don't really understand the calculators and some of the technical information of this topic.

That's what we're here for! To try to make sense out of that for you! The technical jargon of acoustics can be a bit overwhelming the first time you see it, but after a while you'll start getting your head around it, and it will make a bit more sense.

But what would really help us to give you better advices, is to have some photos of that room as it is right now, plus a REW analysis of it, which will give clear indications of where the problems are, so we can suggest ways of dealing with them.


- Stuart -

[johnlee]

Firstly, Thanks so much for the info and suggestions Stuart. Very helpful indeed... and very generous.

I knew I'd forget some things in the initial post. One being that the room is constructed of 2 layers of 10mm plasterboard walls/ceiling and the floor is solid concrete (painted). It's on the second floor of an industrial warehouse.

And yes, I deliberately chose those dimensions from Sepmeyer's best ratios

I didn't include photos because I was hoping the room would be considered a clean slate/blank canvas.

So I'll do as suggested and go ahead and construct bass traps in the corners, rear wall absorption, absorption in all 1st reflection points, a hard backed angled cloud, and perhaps slot walls. Once that's done I'll take some photos and do a REW analysis of the room.

But could I please get a little more detail about this basic acoustic treatment, such as dimensions, locations (especially angled cloud) and materials? I will be using Tontine Acoustisorb 2 & 3 in varying thickness as the "insulation" material. http://www.tontineinsulation.com.au/products/acoustic

As an example I was planning on constructing corner traps with 100mm Acoustisorb2 cut into 600x600x850mm triangles stacked to the ceiling and covered with felt but it seems perhaps a more solid membrane like 10mm ply might be more suitable? And would a traingle of different dimensions be better?

And yes, I'm more than happy to lose up to a meter from the corner of my outside window.

I think for the time being I'll avoid soffit mounting and go with stands as described.

Thanks gain.

[Soundman2020]

I knew I'd forget some things in the initial post.

Yup, but what I was referring to is more in your profile than your post! Here's a link to the forum rules for posting (click here)...

One being that the room is constructed of 2 layers of 10mm plasterboard walls/ceiling and the floor is solid concrete (painted). It's on the second floor of an industrial warehouse.

Very useful and important information! It's a pity that they used 10mm drywall (plasterboard), since 10mm isn't very good for isolation: too light and too flexible, and the resonant characteristics aren't great. 2 layers of 16mm drywall would have been much better. But it is what it is, so I guess you'll have to live with that. You might end up having some type of issues within the room if that drywall vibrates.

If you really wanted to fix that, you could add a layer of 16mm drywall on top of what is there already, with a layer of Green Glue in between. That would make a big difference.

I didn't include photos because I was hoping the room would be considered a clean slate/blank canvas.

Yes, but it helps a lot if we can see what you can see! For example, from what you say and from the analysis I did, I'm deducing that there is little or no bass trapping in there, but it would have been so much easier to just see that directly on the photos! There might also be other things in there that you didn't think were important to mention but that in reality could have acoustic consequences. Air vents, electrical outlets, cupboards, light fittings, fireplace, furniture, etc. Photos are always useful for understanding the room.

Once that's done I'll take some photos and do a REW analysis of the room.

Do that BEFORE you start as well, so that you have a base-line for comparison. Particularly the REW analysis is VERY important: do one test in the empty room, before you even start installing any treatment at all, then repeat the test once the treatment is in to see how much of an effect it had, and what still remains to be done. It is important that you position the mic and speaker in exactly the same locations for all tests: even a few mm can make a difference. So make sure you measure and mark the exact positions of the mic and speaker very accurately, in all three dimensions, so you can repeat the tests validly. If they are not in the same positions, then you cannot compare the test results each time.

But could I please get a little more detail about this basic acoustic treatment, such as dimensions, locations (especially angled cloud) and materials?

No problem!

I will be using Tontine Acoustisorb 2 & 3 in varying thickness as the "insulation" material. http://www.tontineinsulation.com.au/products/acoustic

I'm not familiar with that, but I'll take a look at their specs and see what it does. You didn't mention what your budget is for this, but if it is tight then you might also consider plain old mineral wool insulation, or plain old fiberglass insulation, both of which work very well and are not expensive.

I was planning on constructing corner traps with 100mm Acoustisorb2 cut into 600x600x850mm triangles stacked to the ceiling

That will work fine: That's the basic concept of the "Superchunk" bass trap, and your dimensions are good.

and covered with felt but it seems perhaps a more solid membrane like 10mm ply might be more suitable?

Perhaps, but this is one reason why you should measure the acoustic response of the room several times as you work. For example, once the superchunks are in, measure to see if they are sucking up too much of the high frequency energy (pretty sure they will be!), then try first stretching with ordinary plastic sheeting across the front of your frame, test again. The plastic will reflect back some of the highs to the room, allowing all of the lows through to the trap. The test will show if that is enough, or if you might need two layers of plastic, or maybe something more substantial, lie melamine or wood. You might even need it perforated. Etc.

And yes, I'm more than happy to lose up to a meter from the corner of my outside window.

Great! I'd try to make it symmetrical: However much distance there is between the left wall and the left edge of the window should be the same on the right. Symmetry is VERY important in the front part of the room.

for the time being I'll avoid soffit mounting and go with stands as described.

HAve you looked into the benefits that soffit mounting gives you? It is well worthwhile doing, if you have the budget and the time. The results are pretty amazing. In fact, personally I think it's the best thing you can do for your room, next to treating it properly.

Anyway, I'll take a look at that treatment manufacturer, and get back to you on dimensions.

- Stuart -

[johnlee]

Thanks Stuart ! ! !

I see my location wasn't in my profile. Sorry about that. I did read how important that is and was sure I filled in this detail when I signed up..... Hope that's it

At this stage I could still add a layer of 16mm plasterboard to the room in future. But I'm too busy to do it right now. Hopefully the current construction won't cause too many issues.

I see your point about photos. To be honest the room is currently filled with all sorts of equipment and...... stuff.... while I Build and paint the adjacent room. Hence, no pictures for now I'm sorry.

To explain further I've got a 2 week window between jobs and I'm trying to to get as much construction, acoustic treatment, painting etc done until the next job starts. Hopefully in a couple of days I'll be able to clear the room completely and start as you suggest with a REW analysis. Then, due to time restraints, I'll go straight into making the basic treatment you suggest and then set up all the gear again (by the start of next week!!!!!). My whole studio build is based on doing what I can when I can. My budget for the acoustic treatment is about $AU1000 but this can be stretched out. My main restraint at this stage is time.

Thanks for looking into Tontine Acoustisorb. I like working with this. It's a poly blend with low toxicity.

I've got room to go wider across the rear with the Superchunk. Would it be better bigger or wider? Maybe one across the top horizontal corner too? Thinking about aesthetics, would a plastic layer go behind a felt cover? I just read that some people do this.

I know what you're saying about symmetry and I've thought about it a lot but want to keep as much of the window as possible.

I'll look into soffit mounting at a later stage.

I look forward to hearing your suggestion. And thanks so much ! ! !