Up until now I've used a home-based studio for arranging and pre-producing tracks for the "real" studio, and haven't really worried about acoustics... but that's about to change - I've finally got the budget, the space - and hopefully the ears and experience (after working alongside established engineers and producers) to tackle more serious projects on my own.
But - the sound treatment...! Here's a plan of my room - it's 12' x 16' and 9' ceiling. Concrete/brick walls and hardwood parquet floor. The front wall is mostly glass - 7th floor view over Cape Town. The door in the back wall is the only access
I can't afford the commercial traps (transport etc.) so I'm doing what most of the rest of you do. The yellow blocks are the traps, but the best fibreglass I've found so far is 2" 64kg/m3. I'm still looking for some denser material, but this is what I've found so far.
My question is: for the corner traps (these will be flat traps across the corners) is there an advantage to going TRIPLE sheets - i.e. 6" thick for even lower bass absorption? They will be 2' x 8', to cover almost the full reach to the ceiling.
I was thinking of using 4" for the front and rear walls, and 2" for the side walls and ceiling over the monitoring position.
Monitoring is by Genelec 8030/7050B sub, and I've got the 38% mix position, slightly off-set laterally. There will be a persian rug under the mix position, rest of the floor left open.
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Singer-songwriter-creativityjunkie
The sound of freefall: www.ianhenderson.net
64 kG stuff is dense enough - generally 3-4 PSF (48-64 kG/m^3) works best.
If possible, I'd widen those front corner traps to at least 3 feet wide. And if your material has any sort of membrane on either side, I'd remove it. I'd also widen the two absorbers behind your speakers, and move them further from the wall and closer to the backs of the speakers. This should help smooth the low end response by lessening SBIR between the speakers and the wall behind them... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
Cool, thanks... great having the top guys take such an interest. BTW, what is SBIR?
If I mount the traps behind the speakers on stands should I get them close up behind the speakers?
Which thickness (4") do you recommend behind the speakers?
So far I've only found panels in 0.6 x 1.2m x 50mm (2' x 4' x 2"). For the corner traps I was thinking 2 panels on top of each other, and 3 panels thick, for 2' x 8' x 6". Just checked the room, and I could go 4' x 8' x 6" in the corners, and it would fit fine. Is bigger again better here - these will leave a fairly big air pocket at the back behind the panel!
Should the fibreglass be glued together (end to end and in the sandwich) or is it fine to just "stack it" in the frame?
If the product I can find is the same size and density, is it going to have the same acoustic properties? (In which case I go for the cheapest) Or is there some other way of telling which product is better?
Thanks, once again...
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Singer-songwriter-creativityjunkie
The sound of freefall: www.ianhenderson.net
SBIR stands for Speaker Boundary Interference Response - lower frequencies "wrap around" a speaker box and bounce off the walls and other "boundaries" - when this reflection is in phase with the direct sound, you get a boost at that frequency. When the reflection is OUT of phase with the direct sound, you get a cancellation. This makes for some pretty uneven frequency response especially for unsoffited speakers. Placing fairly thick absorption behind the speakers helps absorb much of the indirect sound so it doesn't interfere with the direct sound, giving a much clearer response in the lower range of the speaker.
If I mount the traps behind the speakers on stands should I get them close up behind the speakers?
This is one of those "cut and try" things - it will partially depend on how far from the walls your speakers are, as well as cabinet shape, etc - this is best done by measurement with a program like ETF, comparing the LF response with different positions of the absorbers relative to walls and speakers.
A good starting place for 4" thick material is 4" away from the wall, with ALL edges of the absorber visible and the speaker covering the rough center of the absorber. At least 3 feet square for each absorber would be minimum.
Then, try moving the absorbers further from the wall and closer to the speakers and re-test. The location that gives the least amplitude of peaks and dips is what you want.
Also, be aware that programs like ETF are VERY sensitive to ALL objects in the room; so you either need to be OUT of the room or in EXACTLY the same place for each and every measurement, or you will get non-repeatable results and end up more confused than when you started...
Which thickness (4") do you recommend behind the speakers?
4" would be the least thickness I'd use, but I don't think more than 6" would be necessary.
So far I've only found panels in 0.6 x 1.2m x 50mm (2' x 4' x 2"). For the corner traps I was thinking 2 panels on top of each other, and 3 panels thick, for 2' x 8' x 6". Just checked the room, and I could go 4' x 8' x 6" in the corners, and it would fit fine. Is bigger again better here - these will leave a fairly big air pocket at the back behind the panel!
If you have room for those larger panels, I'd do it; the extra depth to the wall will give you better LF absorption, and any room smaller than about 12 x 10 x 4 meters almost cannot have too much LF trapping.
Should the fibreglass be glued together (end to end and in the sandwich) or is it fine to just "stack it" in the frame?
It can just be stacked; gluing won't hurt as long as it's just edges or maybe an X shaped bead across the faces, but full-surface gluing will result in an inner membrane that will hurt your absorption.
If the product I can find is the same size and density, is it going to have the same acoustic properties? (In which case I go for the cheapest) Or is there some other way of telling which product is better?
For the most part, when considering products like rigid fiberglass, rockwool, mineral wool, slag wool, the density has more to do with performance than anything. So it's more sensible to look for 3 PCF materials and then shop for price.
If you think you want your room to stay a bit brighter but still need LF trapping, a product with a membrane attached to one side can be used; this side would face the room for a corner trap. IF you're doubling this type material though, you need to REMOVE the membrane for all but the front layer... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
