Ideas for room acoustics - Mastering room

[DeeDrive]

I've been looking over Ethan's DIY bass trap designs, and I trying to figure out what would be the best traps to go with would be. I am unsure of how tall to make them, and also what the best placement would be. My room will be used mainly for mastering, so I'm looking for the flatest response possible, and bass is hugely important.

I've included some rough sketches of the room at the bottom of this post. What would you guys do in this situation? Feel free to be as specific as possible, I want to get all the input I can. Would you use 703 fiberglass for bass traps or 705? I've seen a lot of people talk about 4" 703 panels, but Ethan's designs call for 1". Would there be a disadvantage to using 4" of 703, is this overkill?

It seems like the more I read on this subject, the more unsure I am of what I thought I knew, so if anyone can give some specific advice on what would be best for this type of room, I would really appreciate it.

Also, are there any specific problems I might encounter with the odd shape of the room? Is this shape typically better or worse for acoustics? It seems like there would be less parallel wall space, which sounds good, but does this room shape have it's own issues I should be aware of?

[jayfrigo]

Originally Posted by DeeDrive

I've been looking over Ethan's DIY bass trap designs, and I trying to figure out what would be the best traps to go with would be. I am unsure of how tall to make them, and also what the best placement would be. My room will be used mainly for mastering, so I'm looking for the flatest response possible, and bass is hugely important.

I've included some rough sketches of the room at the bottom of this post. What would you guys do in this situation? Feel free to be as specific as possible, I want to get all the input I can. Would you use 703 fiberglass for bass traps or 705? I've seen a lot of people talk about 4" 703 panels, but Ethan's designs call for 1". Would there be a disadvantage to using 4" of 703, is this overkill?

It seems like the more I read on this subject, the more unsure I am of what I thought I knew, so if anyone can give some specific advice on what would be best for this type of room, I would really appreciate it.

Also, are there any specific problems I might encounter with the odd shape of the room? Is this shape typically better or worse for acoustics? It seems like there would be less parallel wall space, which sounds good, but does this room shape have it's own issues I should be aware of?

I don't want to sound discouraging, but that room looks like an acoustical nightmare. A 12' X 12' square is not going to be your friend. The low ceiling, especially with the even lower angled sides will cause trouble as well. You won't get very accurate sound out of this room, certainly not a response suitable for mastering. As a small composer's suite it could be a nice little room, but as a mastering suite it will be disappointing.

You'll need plenty of targeted trapping at the frequency whose wavelength is twice the room dimension and multiples as well. So, where both dimensions are 12' (ignoring the height dimension and non-axial modes), you look for the frequency with a 24' wavelength, and wavelength = c/f, where c is the speed of sound, and f is the frequency. C=1130 ft./sec at 70 deg. F at sea level, (or 344 meters/sec.), so 1130/f=24. Another way to say it is f=1130/24, which gives you a standing wave at 47.083 Hz, and harmonics thereof.

Traditional traps require 1/4 wavelength traps to absorb the bass, so a 6 ft. trap is probably out of the question, as is a 3 ft. trap even if you only wanted to get the next harmonic. That's where the membrane absorbers come in. You can certainly make a 94 Hz trap that is shallow enough to hang on the wall. That 47 Hz wave is still going to be trouble though.

You could construct several Helmholtz resonators, though that's not very easy. I could give you the math if you wanted to try. They can actually be pretty reasonably sized, especially if you can put the resonant cavity in an adjoining space. I'm guessing that the angles in the ceiling are due to a roof above you, which implies there's a triangular cavity above the flat part of the ceiling that you can use for trapping bass.

You'll also need absorption to eliminate first reflections, including those angled ceiling areas. I'd use 703, and using 4" is not going to provide meaningful help for the bass. You need membrane traps where 1" of 703 inside will do. Those kinds of traps don't work in the same way as just having deeper frictional absorbers. I'm not sure of how much more to say... Is there anywhere else you can set up your studio? I really don't want to be so negative, but this room will give you trouble no matter what you do. Sorry to be the bearer of bad news, and please don't shoot the messenger!

[A101]

That room is square (12’x12’), which is NOT good.
Along with Ethan’s tips check this place out for construction techniques.
I would highly recommended RealTraps panels especially to control bass frequencies.
After all your room acoustics will effect your sound more than your slutty gear.

[Ethan Winer]

> your room acoustics will effect your sound more than your slutty gear. <

Testify, brother!

--Ethan

[DeeDrive]

Thanks for the info guys. Sorry to hear I'm going to have so many problems it looks like. Are there plans anywhere for bass traps that can handle freq's as low as ~47 Hz?

Where would you guys place bass traps in a room like this? On the angled walls maybe? I was thinking maybe on the ceiling, right over the console and listening position, due to the standing wave that would be created by the ceiling and floor being parallel. Or would the back walls be the best place? Should I stradle the corners with traps or keep them flat on the walls?

Also, does anyone else have any more info on the effects of these angles walls?

[Ethan Winer]

Dee,

> Are there plans anywhere for bass traps that can handle freq's as low as ~47 Hz? <

Your main problems are going to be a bit higher than that - probably the 2nd harmonic of that mode and the higher harmonics up to around 300 Hz. But good "normal" (non-tuned) bass traps can handle 47 Hz too.

> Where would you guys place bass traps in a room like this? <

Start with the corners.

> Should I stradle the corners with traps <

Yes, exactly.

> does anyone else have any more info on the effects of these angles walls? <

Angled walls mainly avoid flutter echo between parallel surfaces, which is good. But they have no real affect at bass frequencies.

--Ethan

[jajjguy]

Originally Posted by DeeDrive

Also, does anyone else have any more info on the effects of these angles walls?

It looks like these walls will reflect sound from the speakers right to your ears. This is bad, because the interference between the sound you get directly from the speakers and the sound you get off the walls will create comb-filtering and mess up your frequency response. This is exactly the same effect that happens in every room with ordinary walls, so nothing tragic. Address it by putting absorption on these surfaces, just at the spots where sound will reflect right from the speaker to your head. ("First reflection points.") Use a mirror to help find these spots: put the mirror on the surface, if you can see the speaker from the mix position, then that spot needs absorption.
This is a separate issue from your need for broadband (especially low freq) absorption.

[DeeDrive]

> Should I stradle the corners with traps <

Yes, exactly.

--Ethan

Ethan, I have the design for the wall-mounted bass traps from your website, but these plans include attaching the traps flat on the walls. How can I use these traps to stradle the corners? Should I use a backing material? Is so, what kind, more plywood perhaps? Also, how do you recommend attaching these traps to a corner? Thanks for your help.

[Ethan Winer]

Dee,

> wall-mounted bass traps from your website ... How can I use these traps to stradle the corners? <

You can't. Or, rather, you shouldn't. That type of trap works on an opposite principle of traps that are meant to straddle corners.

--Ethan

[DeeDrive]

Thanks Ethan,

What king of traps are good for stradling corners? Are there any plans for these kind of traps around?

[Ethan Winer]

Dee,

> What king of traps are good for stradling corners? Are there any plans for these kind of traps around? <

Besides the traps my company sells, there's a ton of DIY information and advice in my Acoustics FAQ:

www.ethanwiner.com/acoustics.html

--Ethan

[mltamisin]

4" thick 703 will provide some bass absorption. Get 2'x4' panels and stack them up in the corners. Cover them with a porous fabric for aesthetics if you want. Try the old breathe through test. If you can breathe through the fabric it should be OK. Diffuse your ceiling and the angled wall/ceiling part with quality RPG diffusers. Do the mirror trick as stated above and apply more 4" thick 703 in those areas of the wall. Float them off the wall with 3" of wooden spacers. If you have money I highly recommed Ethan's Bass traps. Apply as many diffusers as possible behind you to diffuse the reflections. Get a shitload of 4" thick 703 or Ethan's traps. Membrane traps will only effectively work on certain frequencies and require the entire wall surface to be treated to be of use. Treat any corner you can treat...save your money on the good shit. Auralex stuff sucks. Don't waste your change. Look at their new diffusers....they're just like RPG's hemifuser. It's simply an acknowledgement that their diffuser designs just don't work. Get RPG's skylines and hemifusers....even if you can only afford a few at a time. They're reasonably priced and work really well. Ebay has some folks selling acoustical foam really cheap if you opt to go that route.
Thanks - Matt

[Glenn Kuras]

"Ebay has some folks selling acoustical foam really cheap if you opt to go that route."
Most of that foam stuff on ebay is a scam!! The numbers are bogus.. All they did was a cut and paste from Auralex. But even at that the Auralex stuff is not going to reach the low end that you need.
We just got back from the Riverside lab doing testing. I can not press upon you how much better straddling corners are. Don't forget that floor to wall corners are just as good as wall to wall corners..

Glenn

[DeeDrive]

Thanks for all your helps guys. I think I can at least start putting together some acoustic treatment for this room. I'll probably just get some 703 and try a few different things, maybe start by putting it in the corners, see how that works, and maybe try building flames and making the membrane traps as shown on ethan's site.

By the way, Ethan, I watched the product videos on the RealTraps site, very nice job! A lot of great information and a lot of fun to watch!

As for the "Foam By Mail" or "Foam Factory" as I think they're called on ebay, I had a bad experience with them a few years back. I ordered "Beige" colored foam as they called it, which turned out to really be "Pink" colored foam. Then, after being up on the wall for a few months, parts of the foam began to change color, (due to lighting conditions, no doubt"). According to their site, their foam "does not change color over time", and when I called them on this, they basically just told me to screw off, and offered no chance to return or exchange they foam. Besides this, the stuff is nowhere near as dense as Auralex, which they claim to be. I'll stop my ranting now, just thought I'd share a bad experience with some dishonest business folks.

[Ethan Winer]

Dee,

> I watched the product videos on the RealTraps site, very nice job! A lot of great information and a lot of fun to watch! <

Thanks!

> As for the "Foam By Mail" or "Foam Factory" ... I ordered "Beige" colored foam as they called it, which turned out to really be "Pink" colored foam. <

Wrong and fading colors is the least of the problems with them! As Glenn said, the real issue is they sell cheap ineffective mattress foam falsely claiming it is acoustic foam.

--Ethan

[DeeDrive]

I've been thinking it over, and I think this is what I'll do to start with:

Get some 2" thick 703 to make (6) 4" panels and stradle the corners, and place 2 panels at the first reflection points (spaced 4" off the wall). I'm thinking of not getting the FRK kind of 703, simply because I'm sure I could use SOME mid/high absortion, and this doesn't sound like enough to deaded the room THAT much.

The main thing I'm concerned with is flattening the response for accurate listening, I won't do too much live recording in this room, so I don't care if it's too dead anyway.

After I get the corners and 1st reflections tamed, I'll do some tests on the really low bass (40-80 hz maybe), and see how bad this area looks. If it still needs some treatment, I'll get a few pieces of 1" 703 and building some membrane absorbers.

Also, I think I might put some 2" foam around in a few areas to tame any other mid/high reflections that might be lurking around, (mainly because I've got a stack of it serving no purpose in my closet.

What do you guys think? Is this a pretty safe plan? Any changes I could make that would increase my chances for success? Also, is there really any disadvantage to having a mastering room that is "too dead". I figure as long as the freq. response is flat, and the main reflections are tamed, I'll be ok. Am I missing something here? thanks for everybody's help.

[Glenn Kuras]

I am NOT big on foam, but if you do go with that then I would cover the other panels with the FRK... Foam can make a room go dead but leave the low end bouncing all over the place. With a room like yours I would really start with all of them with the FRK and then see how it goes... If there is to much high end then put a few 2" panels up with them spaced off the wall two inches..
Trust me your low end is your biggest problem right now.. So deal with that first..

[DeeDrive]

Ok, so maybe I'll just get the FRK-less 703, and ditch the 2" foam. It just seems a shame to pay extra for FRK, and then still need something for the mids/highs. Kill two birds with one stone kinda with getting the regular 703.

Also, I was looking at the absorbtion coefficients, seen here:

http://www.bobgolds.com/AbsorptionCoefficients.htm

and it looks like 6" 703 would do an even better job at 125hz, which is right around my problem area. Does anybody know how this would do at around 50-125hz, or is this membrane-trap territory? Or do you guys think 6" 703 might be overkill?

[Glenn Kuras]

"Does anybody know how this would do at around 50-125hz, or is this membrane-trap territory? Or do you guys think 6" 703 might be overkill?"

No way to know until you test it in a sound lab.. 6" is not over kill at all, but look over the cost. Our panel is tested at 2.02 Absorption Coefficients at 80Hz when straddling corners and those are 4" thick. But ours are not just fiberglass so not sure what making them yourself will get you at 80Hz.. I am not trying to sell you our stuff but if you are having problems in that area you might be better off buying instead of building.. If you would like, PM me and I can send you testing data for you to look over.

Glenn

[Frequency]

Set your studio up outdoors. No reflections from any walls.

[djui5]

What about Thermafiber Mineral Wool "Sound Attentuation Fire Blankets", 2" thick sheets? I bought it cheap, $50 for 12 of these 2'x4' bad boys....

That's what I used for my mix room. I haven't tested it out with speakers yet, but I'm curious if any of you have ever used it.


*warning, PDF links*

Here is some info about the stuff

http://www.thermafiber.com/pdfs/SAFB.pdf

Here's the absorption coefficients. It's the 2.5 pcf density 2".

http://www.thermafiber.com/pdfs/NRC%20Data%20Sheet.pdf

[Anderson]

For a serious mastering studio, get an acoustician specialized in studio design. It's the only way not to waiste your time... and lots of your money. Mastering is a very hard job. IMHO there can't be much compromise with gear or acoustics in that field in particular.

Look around for a Pro to help you! It's not cheap, agreed, but cheaper than doing something yourself, realizing you still have problems, and then having to ask a Pro anyway.

Cheers