John Sayers' Recording Studio Design Forum Archive

Looking good!

Quick question (haven't come across this myself before) - why have you had to extend and loop the pipes for the mini-split air con unit?

Thanks
Gareth

garethmetcalf wrote:Looking good!

Quick question (haven't come across this myself before) - why have you had to extend and loop the pipes for the mini-split air con unit?

Thanks
Gareth

I read in one post ages ago Stuart saying it might help the unavoidable flanking that the air con copper brings to have a loop of the copper in a big circle before you exit the outer wall. Stuart can correct me if I made that up. I don't know how big a deal it is. Also, we ended up with loads of spare copper anyway! So I'm not sure I needed that extra bit.

I read in one post ages ago Stuart saying it might help the unavoidable flanking that the air con copper brings to have a loop of the copper in a big circle before you exit the outer wall.

Right! You did not make it up. If you are looking for very high levels of isolation, then eliminating all flanking paths is important. Copper pipe is rigid, and conducts sound rather well. If it runs directly across the cavity, it carries that sound straight through the wall. By looping the pipe inside the wall, or at least not taking it straight across, you can help to reduce the sound transmission through that path.

It might not be a huge thing, but think of this: If you can find a dozen things to do in your studio that each improve the isolation by just half a decibel, then you improved the overall isolation by six dB! (If you find twenty such things, then you double your isolation, subjectively....)

- Stuart -

Thanks - makes sense that everything is incremental. It's like if you use a great mic pre-amp, on one track you don't necessarily notice, but across 20-30 channels of a mix you start to get a cumulative improvement.

My other question is about whether you are extracting the 'old' air and having a passive air inlet, or whether it's better to force fresh air in and have a passive outlet.. Fans seem to perform better at sucking than blowing, so to speak..?

Cheers
Gareth

My other question is about whether you are extracting the 'old' air and having a passive air inlet, or whether it's better to force fresh air in and have a passive outlet.. Fans seem to perform better at sucking than blowing, so to speak..?

There's two schools of thought on that. One says that blowing air in "pressurizes" the room slightly, which helps to keep the door closed against the seals, improving the seal, whereas if you suck air out, you are creating a slight negative pressure in the room, which tends to open the door, reducing the effectiveness of the seals. To that I say: Get a better door closer! If you have a door closer that is doing it's job correctly, it will certainly be able to keep a good seal, even in the presence of the slight "negative pressure" produces by the fan. That's a non-issue. Another argument is that if you are blowing air into the room and you do open the door, you are still pumping clean, filtered air into the room, because your filters are on the intake duct, whereas if you have an extraction fan sucking air out, with the door open you are sucking in some non-filtered air through the open doorway, so your outlet duct can have dust, pollen, and other nasties building up inside it. That's true, but I'm not convinced that it is much of an issue, unless you like to have your door open for very long periods of time, and in any case I always recommend putting a filter on the outlet registers, regardless! If you do that, it's another non-issue. Plus, if you open the door with an intake blower that feeds into an AHU, then your conditioned air is escaping through the door! If you open your door with an exhaust extractor, your conditioned air on the inlet is still flowing through the room, the way it is supposed to, albeit mixed with some unconditioned air.

I prefer to put an extraction fan on the exhaust end of the system, for several reasons: firstly, as you say, fans do seem to suck better than they blow. Secondly, the noisy part is downstream from the room, not upstream, so the airflow helps slightly to keep the noise going the right way. Third, the rotating blades on the fan creates massive turbulence, implying noisy air: If that is on the supply end, you have turbulent, noisy airflow inside your ducts for quite a distance, whereas if you are extracting, that turbulence goes into the outside world, not into your ducts. Four, if you have more than just one room, then you can combine the exhaust ducts from two or more rooms into ins single final silencer box and one single final fan, successfully. If you have a blower on the supply end, you can't really do that very well, as the flow won't necessarily split the way you want it to, with the correct flow rate going down each duct... unless you design very carefully to get the correct static pressure in each branch, so that you automatically get the right flow, or use damper valves on some of the branches...

Overall, I think there's more to be said in favor of sucking air out the far end, rather than blowing it into the intake.

- Stuart -

Today was a day for getting things wrong!

Firstly I wasn't around, but had fully briefed my carpenter how to do the doors. Then he was on the phone to me saying it wasn't working and I had to come back and sort it out. I wouldn't have anyone working un-attended again. (How many people have rubber seals on their doors? Basically every job is pretty much new to these guys)

Turns out he had a point though and I had not researched the door situation well enough. I had done a lot of looking around and had not found the Rod car rubber stuff, and had only found the weedy foam rubber strips and a 10mm x 10mm proper rubber strip. I was pleased to find this at all as it seemed to be the right kind of material.

The basic problem, and beginner alert here, was that on the hinge side, the door was hitting the rubber from the side, not from the front and that was stopping the door closing. The carpenter then brought the hinge further out, but that meant the door wasn't closing tight enough on the non-hinge side. So I need to find a new solution.

Would also appreciate links to any builds that got the seals spot on, especially any that used square rubber strips (if there are any!)

If he already brought the hinges out such that the hinge side closes OK with a good seal, then I would suggest attaching a shim of some type to the other edge of the door leaf: Perhaps a strip of aluminium just thick enough to make the seal. Along the top and bottom he might have to cut an angled rabbet into the wood, to get the angle correct....

I normally just suggest buying proper acoustic door seals from a specialist company, such as Zero International or someone similar. They have all kinds of seals for all kinds of doors and situations, many of them are adjustable. They are expensive, though, and you'd probably have to import them into RSA... Not sure if they have a rep or distribution center there....

However, it's probably too late for that now!

Another "however": Weatherstrip foam might not do the job. Some types of foam like that are porous. It stops the water getting in, but not so good on the sound. Is the foam breathable?


- Stuart -

After a hiatus, I am trying to get back on the bandwagon. I think I took it at too much of a sprint and burned myself out a little, and then ran out of allotted time with my builder.

Here is how it's looking so far - and I should say, it already impresses me no end how I can see cars but not hear them!
I've covered all fibreglass for now with plastic as I had a bad few days where I hadn't done that and fibres were coming into my house through the door - wish I had done it straightaway. For some reason I was obsessing about getting the right plastic, but in the end I just got some drop sheets from the hardware store and at least they contain the fibres as I am now working in here even though it's not finished yet.

Still to do:
- soffits
- rear bass traps
- rubbing sealing on doors
- cloth
- some slats (they also look cool so i hope I need them!)

I am mainly doing my video work, so it's not such a big deal that the sound isn't yet right. Even so, listening to music in the chair is impressive sounding to my ears, in terms of sounding "tight" and being able to hear the instruments.

I had a go at getting REW going, for interest as much as anything - to track the progress from here. I haven't got any bass trapping in yet, nor the soffits so it will be fun to see the changes. I only did it from 30Hz to protect my speakers, but maybe that's unnecessary.
REW file: https://www.dropbox.com/s/tjpjecm2whxw5 ... .mdat?dl=0

I hope I am doing it right. I'm not sure the SPL calibration is quite right - the REW SPL and my SPL do not match even after telling it that I'm reading 75dBC. The soundcard loopback calibration seemed to go fine (and is pretty flat anyway) and I used a downloaded ECM8000 cal file.

One big concern I have, is that I have noticed a bit of tinnitus when sitting in the room and also when in my bed morning and night. I haven't been blasting music in here at all, so I wonder if it's just that my hearing is more sensitive from this process (i.e. that I already had it from abusing my ears 20 years ago in clubs, I'm just noticing it now). Or whether having fully plastic wrap is hitting my ears with a high frequency refelction & doing me no good.

REW file:

The data looks valid, but I'm not really sure what I'm looking at there! Is that just one of the speakers by itself, or both together? Was that measured at the mix position, in the middle of where your head will be?

I hope I am doing it right. I'm not sure the SPL calibration is quite right - the REW SPL and my SPL do not match even after telling it that I'm reading 75dBC.

I don't understand: If you calibrated REW at a certain level, then it should always remain calibrated to that level... unless you changed something! Are you certain that you had only ONE speaker running when you did that calibration? You must do each one individually (with the other one turned off), not both together. And use a level of 80 dBC, with the full-range main speaker pink-noise test signal in REW. Make sure you are not using the sub-woofer calibration signal by accident. (Even though the REW manual says to use 75, actually 80 is correct.)

So you get REW to play out the pink noise tone at -12dB on the REW "preferences" meter, and you make sure that it is going through your complete signal chain at 0 dBu (-20 dbFS for the digital parts of your system), and that signal is getting to just ONE speaker. Then you adjust your speaker volume control for that speaker alone, until you see a level of 85 dBC on your hand-held sound level meter. At that point, you hit the "SPL Meter" button on REW, set it to "SPL", "C" and "S", hit the "Calibrate" button, select "REW Speaker cal signal", and you should then hear the same pink-noise signal as before coming from ONLY the speaker that you are calibrating, and it should still show up as 80 dBC on your hand held meter. You then type the exact number that you are seeing on your hand-held meter, into the "SPL Reading Calibration" box, and hit "finished". Now repeat the same process for the OTHER speaker, all by itself. As a final check, turn on BOTH speakers, send the calibration signal to BOTH speakers, and check that the level is 86 dBC. Don't re-calibrate here! Just check.

That's it! If you do that correctly, then there is no reason why it would the levels would not match in the future. They would only fail to match if you adjsuted something in the signal chain, such as the volume control on the speaker, or the gain control on your console, or the fader position, or the mic. As long as you don't touch any of that, then the sound level in the room and the sound level shown by both your hand-held meter and the REW meter, will all be the same.

I should say, it already impresses me no end how I can see cars but not hear them!

Aren't you glad you came to the forum, and found what you needed here to do that?

So we can say that your isolation goal is achieved?

I've covered all fibreglass for now with plastic ...

Ummmm.... that's not the way to do it.... I'll get into that below. Think of it like this: When you take a shower, do you first put on your raincoat, plastic cap, gloves, and goggles?

For some reason I was obsessing about getting the right plastic,

Pity you didn't listen to your obsession! It was right.... (more on that later...)

in the end I just got some drop sheets from the hardware store and at least they contain the fibres

Right result, wrong method. . .

- some slats (they also look cool so i hope I need them!)

You probably do, but a slat resonators wont' work any more in your room, because you covered the "resonator" part with plastic! A slot resonator is a tuned device. There's a "slug" of air trapped between the slats, that moves in and out in sympathetic resonance with certain frequencies. What governs that frequency, is the mass of the air that is trapped in there, and the depth of the air cavity behind the slats (from the back of the slat to the surface of the wall behind it). As the slug of air moves in and out, it compresses and expands the air trapped in the cavity, causing it to act like a spring. So you have the mass of the slug of air, and the spring in the cavity behind it. Mass+spring = resonant system. It really, really wants to vibrate a certain frequency. And because you have insulation inside the cavity, that puts a massive damper on the vibrations. So whenever that specific frequency comes along, the things tries to resonate, but can't do that very well, since the insulation damps it, and absorbs the energy. And that's good! It takes energy out of the room at that frequency. So each slot in your slot wall will absorb a certain frequency (or range of frequencies).

Or rather it would have if you built it correctly, but seeing that you put plastic over everything, there is no air connection between the air slug and the spring, thus no resonance, and no absorption....

In other words; because you plastered the entire room with plastic, you now cannot have slot walls. Out of the question. They won't work, even though you do need them. . .

One big concern I have, is that I have noticed a bit of tinnitus when sitting in the room and also when in my bed morning and night.

Probably not entirely due to the room, unless you have been listening at levels that are to high, but maybe partially due to that. More on that later . . .

Or whether having fully plastic wrap is hitting my ears with a high frequency refelction & doing me no good.

Bingo!

I had a go at getting REW going, for interest as much as anything

This is your first measurement, with the empty room. It is your baseline, against which all future measurements will be compared, to see how you are progressing. So far from being "just for interest", this is actually the single most important test you will do! It should be done with the greatest of care, to ensure that it is absolutely valid, and totally accurate.

But anyway: what does it say?

First, the obvious part. Low end waterfall plot:
You clearly don't have any bass trapping in the room! You have very obviously visible modal ringing at 41 Hz, 82 Hz and 123 Hz. In the image above, I'm highlithing your 82Hz mode, as it is pretty big! There's also tiny signs of activity at 164 Hz, and 205 Hz.... Notice the relationship? That's your 1.0.0, 2.0.0, and 3.0.0 modes. In other words, the axial modes related to the length of the room. (Which you said was 4.02 m long). There's also small sings of stuff at 62 Hz and 67 Hz, which would be your 0.1.0 and 0.0.1 modes. There's even signs of tangential and oblique modes. (So much for those silly simple calculators that ignore such modes, claiming they are "not important....").

So, clearly, your next step is getting the bass traps in. Big ones. Deep ones. Large ones. Front and back walls, for sure.

I only did it from 30Hz to protect my speakers,

Protect them from what? From producing sound waves? Isn't that what they are supposed to do? That's like putting plastic covers on your car tyres, to protect them from the road... Since you did not run full-spectrum tests, we can't see what is going on in the very low end of your room. Hopefully, nothing, since your lowest mode is 41 Hz, but there might also be other stuff happening, such as "chuffing" in your speaker reflex ports, or resonances in the room structure...

Now for the sad part:
That's your decay time curve, for the enter spectrum. For usable acoustics, it should look like this:
Flat. That's what you want. The decay times must be the same across the entire spectrum: in other words, all frequencies in the room must die away at the exact same rate, and that rate must be the correct rate for your room: around 170 ms, give or take a bit. Yours is currently around 250 ms, total, but it varies wildly from as little as 60 ms in the mid range to around 280 ms in the high end (can you say "overdone plastic"?), and 350 in the low end! You can see that clearly in the full-spectrum waterfall-plot:
Why is that? Well, it's because you don't have any bass trapping in the low end, you are over-absorbing the mid range, and massively boosting the high end around the entire room because you covered the whole darn thing with thin plastic!!!!

The entire room is now reflective at high frequencies, absorptive at mid frequencies, and resonant in low frequencies.

I have noticed a bit of tinnitus when sitting in the room ...

Yup!


- Stuart -

Soundman2020 wrote:The data looks valid, but I'm not really sure what I'm looking at there! Is that just one of the speakers by itself, or both together? Was that measured at the mix position, in the middle of where your head will be?

OK, I got REW wrong on a few levels. The mic was I thought in the “middle of my head” position, but i got the distance from front wall wrong by 200mm – will be careful from now on. I also hadn’t realised that you calibrate each speaker separately and measure separately and together – will do correctly next time. I had just done them both together.

Soundman2020 wrote:Aren't you glad you came to the forum, and found what you needed here to do that?

Very much!

Soundman2020 wrote:So we can say that your isolation goal is achieved?

I think it’s more than met my expectations, but I do mean to show some outside and inside readings to actually measure the decibel difference for those following – especially as I’m doing things on a lower budget than most, so it’s a good reference for some (e.g. no green glue). I’ve been waiting to finish the door seals before doing that.

Soundman2020 wrote:“I've covered all fibreglass for now with plastic ...”
Ummmm.... that's not the way to do it....

I should have said, that I was planning on taking some of that thin plastic off, at least at the first reflection positions and under the slats – it’s just stapled on, it comes off easily. I did the full cover just for the fibres as I was having a few weeks off in the build process.

But it might be I have to take more than that or all off – I guess REW will guide. I do have some thicker plastic now, which I was going to at least put on the rear superchunks, to keep them as bass only traps.

Soundman2020 wrote:slat resonators ... It really, really wants to vibrate a certain frequency... (or range of frequencies)

So i wonder if I should try to calculate the ideal slat/slot widths to go after my room modes, according to Johns’ calc? (at bottom of page here: http://johnlsayers.com/Recmanual/Pages/ ... encies.htm) Having said that, it seems the norm is to just have 4 or 5 different slat widths and 4 or 5 different slot widths and then you cover a good range. What I don't get is why the suggestion is for slots of 5-20mm or 1/8"-1/2" (3-13mm) when one in theory can get a wider range of coverage than that? For example, if I'm getting the calc right, and given my depth from wall is 108mm, I could go from 49Hz (1mm slot gap, 222mm slat width, 44mm slat depth) to 863Hz (20mm slot width, 32mm slat width, 12mm slat depth). My ideas as to why not are a) that in real life you can't get it working with such big variation or b) the bass traps are dealing with the lows anyway, so focus on the low-mids here or c) if you try to resonate from 49Hz to 863Hz you get dips at certain frequencies, rather than for example a good even reduction over say 150-400Hz. Either way, I’ll do a REW test after my bass traps go in, before slats go in.

I might also try to make a variable depth resonator (like Bigsby's live room, see pic). Is this a no-no in a mastering room? (albeit one in which recordings will be done, but mastering comes first). I don't see why not, in that I can make sure there's no first refelctions from it, and it would give a more even spread of frequencies dealt with & break up some of the box shape of the room. But I'm guessing there's something I'm missing here.

Soundman2020 wrote:This is your first measurement, with the empty room...

Again apologies for not getting REW right and I realise I should have done it before all the 703 went in too.

Soundman2020 wrote:You clearly don't have any bass trapping in the room! You have very obviously visible modal ringing at 41 Hz, 82 Hz and 123 Hz...So, clearly, your next step is getting the bass traps in. Big ones. Deep ones. Large ones. Front and back walls, for sure.

So seeing as the front corners will be mainly soffits and not much of bass trapping, I’m wondering about doing a horizontal trap along the top of the front wall and the ceiling? And I’m wondering if I should do the back corners even bigger than I was planning. Also, is it really worth the time to cut all those little triangles rather than just shove in the whole bag (even leave the plastic wrapping on!) and pack the gaps with other leftovers?

Soundman2020 wrote:”I only did it from 30Hz to protect my speakers]Protect them from what? From producing sound waves? Isn't that what they are supposed to do?

Know nothing about speakers – it’s just that I ran the subwoofer calibration first by accident and the woofer moved in and out in a way that worried me, but good to know.

Soundman2020 wrote:Now for the sad part... all frequencies in the room must die away at the exact same rate, and that rate must be the correct rate for your room: around 170 ms, give or take a bit. Yours is currently around 250 ms, total, but it varies wildly from as little as 60 ms in the mid range to around 280 ms in the high end (can you say "overdone plastic"?), and 350 in the low end!

OK, well lots to be done, and I realise now the vital need of doing REW – how I thought I didn’t have budget for a measurement mic within the whole build cost I don’t know!

Soundman2020 wrote:”I have noticed a bit of tinnitus when sitting in the room ...” Yup!

Well, this is the most serious bit, in that I might have permanently damaged my ears by moving into the room before it was ready. Perhaps it’s short term, time will tell. Again, want to fully document things here even though it’s embarrassing, in order to give something back to the beginners of the future.

For now I have moved out of of the studio and back into my bedroom & have some guys coming tomorrow to carry on with the work. Haven’t yet decided whether the soffits should go all the way to the ceiling yet. I think Stuart you’ve written that it’s the shortest distance of the baffle that counts, in which case in a small room like mine, I wonder if I might as well close it off 50cm from the ceiling and then use that space for bass trapping, like some builds have done.

For fun, here is the waterfall graph in my bedroom at same 200ms scale as the first studio test & then at a whopping 1500ms - I better not do any mixing here!

i got the distance from front wall wrong by 200mm – will be careful from now on. I also hadn’t realised that you calibrate each speaker separately and measure separately and together – will do correctly next time. I had just done them both together.

Now that you figured out what you were doing wrong, how about correcting that and posting another set of REW data?

I do mean to show some outside and inside readings to actually measure the decibel difference for those

Cool! I'd love to see that!

I was planning on taking some of that thin plastic off, at least at the first reflection positions and under the slats – it’s just stapled on, it comes off easily.

I do have some thicker plastic now, which I was going to at least put on the rear superchunks, to keep them as bass only traps.

There's an equation that might help you here. There is a reflection curve for foils (plastic is a foil too, acoustically) that defines the point where foil of any given surface density will be 80% transparent to sound (allowing 80% of that frequency through to the other side, reflecting back 20%, or coefficient of reflection = 0.2). The curve rises to about 99% reflection above that, at about 6 dB/octave, and falls off to practically 0% transparency below that, at the same rate:

F = 90 / m

F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2

Assuming your plastic is polyethylene, the density is approx. 970 kg/m3. If your plastic is something else, you'll have to go hunting for the density.

So i wonder if I should try to calculate the ideal slat/slot widths to go after my room modes,

You already did the math, and you discovered something rather interesting: Even with very broad slats, the slot you need to hit typical modal frequencies is tiny! And you' need to make those slots with incredible precision: if you accidentally made them 1.1mm instead of exactly 1mm, you'd be off by 10%.... And since modes are very tight, very high Q (just a few Hz wide), you'd need NASA spaceship precision to ensure that you get it right. You'd also have to have a amazing HVAC system that controls the temperature and humidity perfectly, and even pressurizes the air in the room, to keep it at exactly laboratory standard conditions, so that the speed of sound will be dead right.... Then, even assuming you did manage all of that, think about this: only 1mm out of every 222mm is actively absorbing that mode. So only 0.4% of your wall area is involved in treating modes.... vs. 100% if you made it all absorption. Finally, there's the issue of location: Your side walls can only treat modes that are associated with the side walls! It sounds rather obvious, but it's easy to forget. Since your side walls never "see" the sound waves that cause modal ringing in the lengthwise or height dimensions of the room, they cannot possible be used to treat any of the x.0.x modes. Only 0.x.0 modes. And there's also the issue of the relationship between the cavity depth and the wavelength....

In other words, forget about using slot walls to hit modal issues! It doesn't work very well. Yes, you could de-tune the resonance (broad Q) to try to cover a wider range and hit several modes at once, but then you'd be lowering the efficiency...

Slot walls are great for the mid range, but not for modal. If you do decide to go with slot walls, then tune them broadband across the low-mids and mids. They are quite good for that: they will tend to gently absorb frequencies below the lowest tuning, to a certain extent, while also diffusing frequencies above the tuning, and reflecting back most of the highs.

4 or 5 different slat widths and 4 or 5 different slot widths and then you cover a good range.

Yep! Some people like the look of having all the slats the exact same width and varying the slot size. Others like to have all the slot sizes identical and vary the slat size. Some like to vary both at once. Personally, I think it looks nice when you follow a sequence: I often start with broad slats at the top and bottom of the wall with small slots, then uses smaller slats as I go inwards from there, with wider slots. So as you look down from the top and bottom of the wall, going towards the middle, the slots get bigger while the slats get smaller. That also places the lowest tuning near the floor and ceiling, and the highest tuning towards ear height, which makes sense acoustically. I think it looks nice, but others might not agree. That's one of those "personal preference things": you can vary slot/slat combinations any way you like to get the results you need. You can even vary the cavity depth: I have been known to divide the cavity into a few individual air-tight sections, and put a layer or two of plywood/MDF/OSB up against the sheathing at the back of the cavity, to leave a smaller (less deep, higher tuned) cavity.

What I don't get is why the suggestion is for slots of 5-20mm or 1/8"-1/2" (3-13mm)

Because there's a practical limit on what will resonate and what won't! Eric Desart suggested that the cavity depth needs to be within the range of about 1/8 to 1/12 of the wavelength you are trying to absorb, and using 1/10 as the rule of thumb. In other words, assuming that your cavity depth is one normal stud at 3.5", then you'd expect to get good results for wavelengths around 35", which is roughly 390 Hz, and allow 20% either side, so 28" to 42" wavelength, so very roughly you could expect to cover the range 300 to 500 Hz quite well with a cavity depth of one 2x4 stud. If you have 2x6 studs (5.5" deep) you could get down to maybe 210 Hz, and if you put two layers of 3/4" plywood in the back of a 2x4 cavity (making it 2" deep) you could get up to maybe 900 Hz. So in reality, a typical slot wall is useful for absorption in the range around 200 Hz to 1 kHz. It will still absorb something a bit beyond those extremes, but less effectively. However, as I mentioned before, that's the tuned range (actual resonance). It will absorb broad-band at a low level in lower frequencies, and it will diffuse and reflect higher frequencies to varying extents. It's a good device, when you understand how it works.

given my depth from wall is 108mm,

How did you get that depth? Where did you find studs that actually measure 4" deep? That's unusual!

I could go from 49Hz (1mm slot gap, 222mm slat width, 44mm slat depth) to 863Hz (20mm slot width, 32mm slat width, 12mm slat depth).

I would suggest tuning in the range 280 to 425 Hz. Call it 250 - 450, to make it simple.

My ideas as to why not are a) that in real life you can't get it working with such big variation

Bingo!

So seeing as the front corners will be mainly soffits and not much of bass trapping,

You'd be surprised at how much trapping you can get in the corner, if you do your soffits right!

I’m wondering about doing a horizontal trap along the top of the front wall and the ceiling?

That can only help!

how I thought I didn’t have budget for a measurement mic within the whole build cost I don’t know!

Haven’t yet decided whether the soffits should go all the way to the ceiling yet. I think Stuart you’ve written that it’s the shortest distance of the baffle that counts, in which case in a small room like mine, I wonder if I might as well close it off 50cm from the ceiling and then use that space for bass trapping, like some builds have done.

Right! It's good to make the soffits taller than they are wide but a good margin, but I do like to leave space above for extra bass trapping.

For fun, here is the waterfall graph in my bedroom at same 200ms scale as the first studio test & then at a whopping 1500ms - I better not do any mixing here!

- Stuart -

Now that you figured out what you were doing wrong, how about correcting that and posting another set of REW data?

I have moved out my desk now so I haven't got anywhere to put the speakers - I’ll do a new test as soon as I get my speakers up on their shelves, before I change the treatment in the room.

I am attempting the Bearfoot soffit approach (http://johnlsayers.com/phpBB2/viewtopic.php?t=718) with the speaker support decoupled from the baffles. Here is what my guys have done so far it feels fairly rigid but could still be beefed up. I am going to put the speaker on a 6mm hard neoprene strip and then use a ratchet strap to clamp it firmly down.

For the baffles, I have a pretty heavy 18mm shutterply board & some nice looking 3mm ply to panel pin / glue to the front. I am nervous that this is a big no-no, that it might vibrate etc. I don’t have a lot more money to spend, so unless this is a disaster, I’d like to stick with it – I can use a lot of glue!

There's an equation that might help you here
F = 90 / m
F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2

I have cut some small rectangles and measured their area and weight. 1) Pink fluffy plastic cover 85cm x 96cm, 53g so 0.053kg and .816m2 so 0.065kg/m2 so F= 1385kHz

2) Foil leftover from roof insulation 116cm x 50cm, 113g so .113kg and 0.58m2 = 0.195kg/m2 so F=462Hz

So I think that foil will be great for the rear bass traps and the other plastic could be used in areas if needed.

"So i wonder if I should try to calculate the ideal slat/slot widths"

Thank you for the great explanation around this – really interesting to know.

Your side walls can only treat modes that are associated with the side walls!

Ah – in this case I will try to do slats on side, ceiling and rear of room.

If you do decide to go with slot walls, then tune them broadband across the low-mids and mids. They are quite good for that: they will tend to gently absorb frequencies below the lowest tuning, to a certain extent, while also diffusing frequencies above the tuning, and reflecting back most of the highs.

Will do

"given my depth from wall is 108mm"
How did you get that depth? Where did you find studs that actually measure 4" deep? That's unusual!

Yes, SA does seem to have unusual sizes compared to the rest of the world.

I would suggest tuning in the range 280 to 425 Hz. Call it 250 - 450, to make it simple.

With the timber I can get easily around here, I can get this range out of the calc:
From 6mm slot, 114mm slat, 25mm deep = 216Hz
to 10mm slot, 38mm slat, 25mm deep = 440Hz

I am attempting the Bearfoot soffit approach ( --- ) with the speaker support decoupled from the baffles.

That's a pretty old thread, Nick. Nearly 15 years. There are better ways of doing things now...

Here is what my guys have done so far

That's a start, but not nearly rigid enough.

I am going to put the speaker on a 6mm hard neoprene strip and then use a ratchet strap to clamp it firmly down.

And how will you ensure that the neoprene really does float your speaker? And the canvas of the strap? Neither of those will "float" if you don't get the math right.

Floating a speaker is exactly the same as floating a floor, just on a much smaller scale. You still need to do the math to make sure that your neoprene pads are compressed by just the right amount to make sure that the speaker remains isolated throughout the frequency range that it will be producing. Ditto for the canvas....

I originally used Barefoot's concept, but I have since developed it into something rather different, that works quite well. That's what I used for Studio Three (and others) ( http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 ). I found that you need a lot more rigidity in the mounting for both the speaker and the baffle, to get that to work well.

I have a pretty heavy 18mm shutterply board ... & some nice looking 3mm ply to panel pin / glue to the front.

That's the bare minimum that you'll need. I usually use much more mass than that on the front baffle. If you could add a layer of 19mm MDF to that "sandwich", you'd be in the ballpark.

SA does seem to have unusual sizes compared to the rest of the world.

Ahh, yes! The good old RSA... known for churing out some strange things! I'd forgotten that you are in the RSA.

With the timber I can get easily around here, I can get this range out of the calc:
From 6mm slot, 114mm slat, 25mm deep = 216Hz
to 10mm slot, 38mm slat, 25mm deep = 440Hz

Sounds good to me! Varying within that range (and a bit beyond it too) should get you some decent lower mid-range performance.

- Stuart -

That's a pretty old thread, Nick. Nearly 15 years.

Oops!

how will you ensure that the neoprene really does float your speaker?

I found this thread (http://www.johnlsayers.com/phpBB2/viewt ... =2&t=11732) with a good explanation on floating from you Stuart and it’s clear to me that the simple answer is I won’t be able to float it. I don’t know the maths nor do I have a fine adjustment tightener (nor have budget to add).

So the question is what is better out of a) a speaker sat on the wooden shelf (which is beefed up btw), b) a speaker sat on neoprene on the shelf and c) the speaker strapped down tight with neoprene around it to the shelf.

My guess and preference is to strap it down – partly so I know it won’t move from position – and in effect surely this makes the speaker heavier (i.e. shelf is part of the speaker cab) and therefore better. I will try to do a direct REW comparison.

Studio Three (and others) http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471

I didn’t see any info in that thread about actually achieving floating speakers (but you can’t give away everything right!), but it has a very good write up on REW tests which I will keep for reference. I know I won’t get anywhere near +/- 3dB from 100 Hz to 8 kHz at 1/3 smoothing – I am +/- 8.3dB at the moment (see graph below), but it’s good to know what I’m aiming for (as well as the flat RT60 / evenly decaying waterfall).

I did another base test in REW following your instructions. I think I did it right (each speaker calibrated to 80dBC – which means the whole graph has shifted up a bit as last time I calibrated both speakers together at 75).

REW links:
L speaker https://www.dropbox.com/s/8u6voysm82y7w ... .mdat?dl=0
R speaker https://www.dropbox.com/s/xmp5swrwxmoec ... .mdat?dl=0
Both speakers https://www.dropbox.com/s/i0k9pyt565p8t ... .mdat?dl=0

Notes

- I hope you don’t mind me posting graphs Stuart? Let me know if there’s any settings I should do differently.

- my SPL is so far above 80 for the single speakers over most of the freq range – but perhaps this is normal for a badly treated room?

- Wear earplugs next time

- the L and R are quite different. I do have the untreated door as one main asymmetry (this will get treated soon). There was also me and my carpenter in there in non-identical positions. I will do the test with just me crouching front centre from now on.

- I only have fairly basic 5” monitors which are listed as rolling off (3dB) at 64Hz which might explain the lack of sub 80Hz on the SPL. Though I don’t know why for the first test I did the roll off was much lower. (Presumably I need to save up for a sub? I have a budget for the room build, but not much for the equipment – though my video social enterprise is starting to pick up now and that money can feed back into the studio). Also, perhaps the baffles will be my friend in this.

Had another go at the rubber seals around my doors. Guess what - failed again! I knew the rubber was a bit too hard (quite a bit harder than car boot rubber), but I thought it would still work and the shape was good. And testing a few cm worked fine. But once fully round the door, it was strong enough to prevent a good seal. It failed the light test and the more sensitive air test - that is with my fan blowing on high into the room, I can feel air seeping through. So back to the drawing board - I am going to try on Monday to buy some rubber that is the same as car boot rubber in stiffness and get it to stay on the frame somehow.

with a good explanation on floating from you Stuart and it’s clear to me that the simple answer is I won’t be able to float it. I don’t know the maths nor do I have a fine adjustment tightener (nor have budget to add).

Can you get Sorbothane where you live? It's much preferable to Neoprene, and easier to calculate...

So the question is what is better out of a) a speaker sat on the wooden shelf (which is beefed up btw), b) a speaker sat on neoprene on the shelf and c) the speaker strapped down tight with neoprene around it to the shelf.

I'd go for D) Sat on a beefed-up version of that shelf, on top of Sorbothane pads, and held down with a "lid on top", with Sorbothane pads there too... (And I'm already giving away a bit much with that! )

I didn’t see any info in that thread about actually achieving floating speakers (but you can’t give away everything right!),

I did another base test in REW following your instructions. ... REW links:

It's easier if you do all three tests inside one single MDAT file... makes it easier to download, and much easier to compare...

- I hope you don’t mind me posting graphs Stuart? Let me know if there’s any settings I should do differently.

No problem! We'll get to that...

- my SPL is so far above 80

Then you did not calibrate correctly! Are you sure you had your hand-held sound level meter set to "C" weighting and "slow") Are you sure you set things up correctly? Are you sure you put the right numbers in the right place in REW to tell it what the real levels are?

- Wear earplugs next time

Yup!

I will do the test with just me crouching front centre from now on.

.... or you could use the "start delay" feature of REW.... that's what it is there for!

- I only have fairly basic 5” monitors which are listed as rolling off (3dB) at 64Hz which might explain the lack of sub 80Hz on the SPL.

Are those going to be your final speakers? Have you considered either upgrading them to something that gets down into the low end, or adding a sub?

(Presumably I need to save up for a sub?

I guess that answers my question above! Yes, a sub ( a good one that goes down nice and low), or replace your current speakers with something that has a better range, and higher precision.

I am going to try on Monday to buy some rubber that is the same as car boot rubber in stiffness and get it to stay on the frame somehow.

On a very tight budget, trying visiting a car junk yard, and get some actual door seals from scrapped cars....


REW data:

First you need to re-calibrate, as your graphs are showing that you did the tests at around 100 dB, which is too high. 86 dB is the "standard" for calibration. Set things up so that your gain control across your entire signal chain is at unity (a 0dB test signal coming in at one end stays as 0 dB everywhere, on all analog meters, and -20 dBFS on all digital meters). Then with REW playing it's full-range pink-noise test signal, and all your faders and controls set at unity, use your hand-held sound level meter and adjust the volume on the speakers themselves so that you are seeing exactly 80 dBC on your hand-held meter with just one speaker on, and 86 dBC with both speakers on. Then run the actual tests.

Second, you are using way too much smoothing on your graphs. Anything above about 1/24 will completely hide modal issues in the low end, and narrow peaks in the mids. When you are looking at the low end (below about 500 Hz), then keep the smoothing to 1/48 or 1/24. For the mid range you can go about higher, maybe 1/12., and for the very high end, maybe 1/6.

You have too much absorption in the mid range, and not enough in the highs. In other words, you probably need thicker plastic on your absorption, with holes or slots cut in it. You can see the problem here:
Next, you have some rather nasty reflections coming in early, at around 5ms and 17ms. Better find out where those are coming from, and deal with them: You seem to have your low end reasonably under control: There's some signs of modal stuff going on, but not too serious. However, it might just be that your speakers don't go down low enough to fully trigger the modal response. When you get your new speakers (or sub), that will change:

I am +/- 8.3dB at the moment (see graph below)

Yes, but you are over-smoothing considerably! With 1/24 smoothing, it's more like +/- 15 dB: So there's quite a bit of work to do still!


- Stuart -