I finally getting ready for wall treatments for small 12'x18'x7.5" theater. I planning on 1" linacoustic for the entire front wall, and at ear height and below on the side and back walls. The upper back and side walls will get 1" worth of poly-batting to fill it out and all will be covered with some dazian epxo cloth fabric.
Whit this small theater I'll have some left over linacoustic from my 100" roll. Assuming I have enough, would this be a good material to use to make 17"x17"x24" super chunk bass traps in the front corners? I read most people are using OC 703 which I think has very similar acoustic properites as the linacoustic. It sounds like the 703 might be more rigid than the linacoustic though. I couldn't find a local dealer for the OC703 so I was hoping the linacoustic would be an acceptable substiute for the 703 for a corner trap.
Another option with the extra linacoustic could be to use 2" instead of 1" on the front wall? I think the bass traps would be more desirable though in the small room.
For the superchunk bass traps, you are going to get recommendations to use R13/R19 pink fluffy insulation instead of linacoustic or 703. In lamens terms, it's because in the corners of your room, there is less velocity so less dense insulation works better. Others can chime in with more details.
As for the front wall, the thicker the better so 2 inch would be a worthwhile use for the rest of your line acoustic. Something else to consider for the front wall is to use a membrane (thin saran wrap type plastic, the stuff construction workers use to lay over carpet while working) in between the layers of your linacoustic. This will help with the lower frequencies a bit more than two layers alone. Again, more detailed info can be had from others, hopefully they will chime in
5000rays/m flow-resistivity (pink fluffy) becomes a good choice at 34" faced chunks and thicker. for 24" faced i would use a material with higher GFR,
regardless, for porous-only (velocity-based) LF absorbers, they need to be sufficiently thick (spaced away from rigid boundary such that the insulation is placed into relative areas of high particle velocity for a given wavelength) to be effective - and the thicker the trap, the lower the GFR of the material you will want to utilize.
So i'd be better off making the screen wall 2" (id have enought to do even 3") and then use the fluffy pink chunks for corner bass traps?
A 100' roll of linacoustic is a little pricey so I'd like to be able the use the leftovers (approx 40' x 4') if at all possible. But at the same time I don't want to use the leftovers if it would produce a negative effect.
there isn't a correlation between "less velocity" and "less dense insulation", as you imply.
...although speed of sound does change in the porous absorber
Oops, I messed that up. I guess I got my words jumbled because of all the bass trap talk... velocity-based traps, pressure-based traps (i.e. non velocity-based traps), etc. I guess velocity isn't the issue in corner traps, not as much as pressure anyway? Although, if the velocity never really changes, why is a higher "GFR" absorber not recommended? Is it because with the higher pressure in the corners, a lower GFR absorber is the key because it's easier to turn pressure into heat? Therefor, velocity is the lesser of the concern?
Thanks for the heads up on that link. That was a great thread (at least the parts I could understand). Since its taken me so long to get to this point already I think I'll try a some experimenting with amount and location of the linacoustic.
The room is currently drywalled and the kids and I have been watching stuff ocassionally down there the last few months. Even in its current unfinished state we all think its sounds pretty good. Thats part of the reason its been taking so long to get the room done, I never should have installed the projector.