John Sayers' Recording Studio Design Forum Archive

How far from the wall are the acoustic panels supposed to be? I'm going to use wooden French Cleats to hang 2" and 4" panels. I might even put up a track so they're movable.

Which panels? For what purpose?

Different panels, in different locations in the room, have different purposes, and might or might not need spacing away from the walls...

- Stuart -

As I said 2” and 4” Acoustic panels. Just general. 3/4”, 1” away from the walls? 4” bass absorbers. Then behind the speakers and drum set. I’m talking about mounting on the wall, not distance from the source.

As I said 2”

2" panels aren't much good for low frequencies where most of room problems exist. Sure there are instances where you'd want to lower the time domain response of higher frequencies and these could apply there. But due to the wavelengths of lower frequencies, these would only work effectively at higher frequencies.

3/4”, 1” away from the walls?

Again, it all depends on what frequencies you're trying to attack. Typically, the further away from the wall, the better (see Bob Gold's absorption coefficient chart)

4” bass absorbers.

I wouldn't call a 4" panel on the wall a bass absorber. It would be called broadband absorber. Bass absorption, to be effective as such, must occur in the corners where modes terminate. Furthermore, super chunks are preferred in the corners as they are much more effective than a single 4" panel strung across the corner. Now, don't get me wrong, a 4" panel in the corner does work. Heck, I have some in the corners in the room I'm sitting in at the moment. However, when placed on a wall, they will work more as a broadband device, not a bass trap.

behind the speakers

Push 4" of absorption right up against the wall. This will get your speakers closer to the wall, increasing the SBIR frequency higher, and ultimately making it easier for us to treat (with the 4" of insulation)

Greg

As I said 2” and 4” Acoustic panels. Just general. 3/4”, 1” away from the walls? 4” bass absorbers. Then behind the speakers and drum set. .

You still didn't answer the question. For what purpose? I already exaplined (in a different thread....) that you need 4" thick panels between the speakers and the front wall, which is why you leave a 4" gap there. 2" panels won't do much, except for mids and highs, so you'd have to say WHY you want to only treat mids, and highs, and WHERE you only want to treat mids and highs, to be able to help you with that. And 4" is nowhere near enough for bass absorption. I usually allow at least 24" depth at the rear of the room for bass trapping, and 36" or even more if the room is big enough. Think of it this way: the wavelength of the lowest note on the bass guitar is about 32 FEET long, so 4" isn't going to do much for that....

I’m talking about mounting on the wall, not distance from the source

So am I! As I said: "... and might or might not need spacing away from the walls... I never mentioned spacing anything away from the source... Not sure where you got that. No idea why anyone would even consider the spacing form the source!

As I said: different panels, depending on purpose and location in the room, might need to be spaced away FROM THE WALLS, or they might not. It's the REASON why you put them there that matters in deciding if you need spacing or not. Unrelated to the distance to the source.


- Stuart -

Ok then, let me ask it different way. Various purposes, how far from the wall. I’m putting up all the panels, tracks, chunks, clouds, diffusers, 2” and 4” panels in four rooms. Various purposes. How far from the wall should panels be under varying circumstances?

Ok then, let me ask it different way. Various purposes, how far from the wall. I’m putting up all the panels, tracks, chunks, clouds, diffusers, 2” and 4” panels in four rooms. Various purposes. How far from the wall should panels be under varying circumstances?

Sorry I can't give you a better answer.... It's simply because NOBODY can answer your question, until you know what the specific problems are in YOUR studio! Not my studio, or Greg's studio, or Steve's studio, or Rod's studio: Yours. Every single studio is different. Each will have it's own specific set of issues that need to be treated. Until you know EXACTLY what those specific issues are in YOUR studio, you can't get an exact answer to your question.

Here's a thread that might interest you, on the process for treating a control room: building and tuning a control room Take a look through that, and you'll get an idea of how the process goes.

Now, maybe you don't need such high precision as the other folks do for your place, and perhaps more generic treatment would be fine for you. Or maybe you need even HIGHER precision acoustics in your room. And either way, your room is very different from theirs, so most of what we are doing there would not even be applicable at all to your room.

That's the issue. I'm not trying to make it hard for you, or lead you on a wild-goose chase, and I'm not trying to avoid answering your questions: It's just that there IS no answer until we know what the problems are.

It's like if you go to the doctor, and ask him "How many pills should I take, and how often should I take them". But you haven't even told him what your symptoms are yet, so he can't even tell you WHICH pills to take, least of all how many / how often!

Yes, there are some general guidelines that work for every room, such as the ones I gave you before about the 4" thick OC-703 panels on the front wall that fill the 4" gap between the speaker and the wall: that always works, with no variations. But I can't tell you what treatment to put on the SIDE walls, or how thick it should be, or if it needs spacing away or not... because I don't know what problems your room has! And even if you did tell me "The bass is poor around 90 Hz.", that STILL wouldn't help, because I would need to know what TYPE of 90 Hz problem you have. Is it modal? SBIR? A reflection? Structural resonance? Something else? There are several things that could cause a 90 Hz problem that you hear as "poor bass", and until you can identify which one of those is causing it, I can't tell you what treatment to use, or where to put that treatment. If it is modal, then the treatment would HAVE to go at a point in the room where that specific mode has a pressure peak. So if the pressure peak is on the rear wall, then putting treatment on the SIDE wall is not going to do a single thing to fix it, even if it is the exact correct TYPE of treatment!

So you are asking questions that can't be answered, until you tell us what is wrong with your room.

There are general things that you WILL need to do, such as massive rear wall bass trapping, and first-reflection point absorption, etc., but even then, the details of those depend on YOUT room.

Sorry to be obtuse, but tuning a room is a process, not just a matter of scattering around a few panels at random. You first need to predict the room response if it hasn't been built yet, so you can modify the design to make it better, and once it has been built, you'll need to test it with acoustic analysis software to identify what the REAL problems ACTUALLY are... then based on that you can put the right treatment in the right places, test again, and repeat until it is as good as you want it to be.

Putting the wrong treatment in the wrong place will either do nothing at all, or it will make things WORSE, not better.



- Stuart -

I would like to broaden to generality. Tests in Labs have shown an increase in LF absorption by using a 1:1 Fibre:Airgap ratio. But this is of quite a large area of fibre, relative to say a single trap.
10 Square Metres vs around just 1.On the other and a full surface area does very well with a 1:16 ratio. A Suspended Ceiling of absorbent tiles of 1" depth has good absorption down to 50Hz.
Conversely I am quite doubtful if a single isolated trap experiences LF extension at all, and would not go beyond 1:1 unless there is very little gapping between panels, in effect almost a full surface area.

Generally speaking, to be of use for a normal studio application, a minimum of 4" of insulation spaced 4" off the wall. Assuming a GFR of 16000-23000, your would have effective absorbtion down to around 200hz, and dropping off steeply from there.

http://www.acousticmodelling.com/porous.php

You can use that calculator to model the relationships between fiber GFR values and depth/airgaps.

Generally speaking, to be of use for a normal studio application, a minimum of 4" of insulation spaced 4" off the wall. Assuming a GFR of 16000-23000, your would have effective absorbtion down to around 200hz, and dropping off steeply from there.

True, and that's a good general rule, but there's some things that the calculator doesn't take into account, it seems. Absorption in the low end is actually better in reality than predicted by that. Case in point is the other room, where you can clearly see the effect that a layer of insulation has at much lower frequencies. This is where he put the insulation in his ceiling, with "before" and "after" waterfall plots in REW:

http://www.johnlsayers.com/phpBB2/viewt ... 8&start=33

All of that was obtained with just 4 1/2" total thickness of insulation (3.5" of rockwool and 1" of fiberglass duct liner), and no air gap. According to the calculators, there should be very little at all happening at 110 Hz, even less at 80 Hz, but you can clearly see the very nice effect in both of those areas.

Here's what prediction says should have happened:
Reality is a bit more interesting. At 100 Hz, it knocked the T20 decay time way down, reducing it by over 250 ms, from about 450ms to about 200ms. That's impressive.


- Stuart -

Right, i agree 100%. Tge most common complaint i see about the online PAC is that it doesnt take into account the membrane effect from having a large surface area or closed perimiter as in corner placement. None the less, the results acheived in that room with just 4" of fiber are encouraging and impressive. This is exactly what DanDan was refering to in his post. I think its saddening that more people dont exploit this free lunch and just stick to small 2'x4'x4" panels spaced sporatically around the room.

Hi Jason, that PAC can be very misleading. From Bob Golds, and Eric Desart, and Andre Vare, etc. fibre panels have absorption of 0.85 and higher when they are only 7% of the wavelength in depth.
That is flat on the boundary, and with airgap to the boundary if the surface area is quite large and contiguous. (One test I have seen). Then there is a edge affect when the area is split into smaller panels. The damped membrane effect, when suspended. Corner effects add greatly to that. Well worth trying a few guessed actually occurring angles of incidence in the PAC, say 70 degrees.....
All good!