absorbtion questions...

[americanruse]

i've been reading up on low frequency absorbers and whatnot, and i've got a couple dumb questions...

what are most 'fake studio walls' made of?

when you have the measurements: 1.8m x 500mm, which one is height and which is width?

in a panel absorber, the two factors that determin the frequency of absorption are (1) mass or density of the panel and (2) the depth of the air cavity. how do those effect the frequency? i'm assuming the deeper the air cavity, the lower the absorbed frequency, but what does the mass do exactly?

is there a big difference between using plywood or fibreboard?

what's a good size for a panel absorber? 3' x 3'?

on a rear wall absorber, do you need to attach the fabric to the wood, or can you just drape it in front?

 

[knightfly]

"what are most 'fake studio walls' made of? "

Fake acoustic treatment. Seriously, this depends on too many factors to generalize. Could be ANYTHING from nothing to slot absorbers, broadband absorption such as rigid fiberglas mounted any distance from the "real" wall, etc. Some bigtime mastering engineers won't even tell you what's behind the cloth - Bob Katz, for one...

"when you have the measurements: 1.8m x 500mm, which one is height and which is width? " -

Of what? There is no set rule for this in anything. Brits and other Euros like the big numbers first on almost everything, including photographs. Acoustic absorbers get mounted wherever there's room and they will work, so could be either orientation.

"in a panel absorber, the two factors that determin the frequency of absorption are (1) mass or density of the panel and (2) the depth of the air cavity. how do those effect the frequency? i'm assuming the deeper the air cavity, the lower the absorbed frequency, but what does the mass do exactly?" -

Same thing - more mass, lower frequency. The formula is Fo= 170/sqrt (M*D), where Fo is resonant frequency, M=mass of panel in pounds per square foot, and D is depth of the air space behind the panel.

"is there a big difference between using plywood or fibreboard?" -

Almost ANY material will work, but fiberboard (masonite, for example) tends to deteriorate easier if ANY moisture is around. Plywood holds up best.

"what's a good size for a panel absorber? 3' x 3'?" -

Depends on where it goes and how much room you have. The larger the area, the more absorption at Fo.

"on a rear wall absorber, do you need to attach the fabric to the wood, or can you just drape it in front?" -

Again, too generic a term. There are several kinds of absorbers. In a panel type, NOTHING should touch the panel, other than some people place spun fiberglas lightly against the inside of the panel for damping, which widens the response and lowers the absorption. In a slot/slat resonator, the cloth is part of the design and needs to be against the inside of the slats. Panel resonators are generally too bright for the rear of a small room, so some mount 1" rigid fiberglas in front of them to tame the highs/mids. This could have cloth wrapped around it, and should. Otherwise, there's too much chance of shedding and airborne particulates.

If you haven't already been there (and even if you have, you probably missed something) check out this site for more info -

http://www.saecollege.de/reference_material/index.html

Hope that helped... Steve

 

[americanruse]

thanks alot. i was already at the sae site, and got everything that i could find off of it. alot of the things you wrote weren't even on there. thanks again.

as for the 1.8m x 500mm, it was just some measurements that the sae site gave for acoustic hangers. they didn't show a picture from the front end... just the side, so i didn't know if it was longer or taller, or if it even matters.

i had another question that i forgot to ask:
is there any insulation that is better than others for acoustic hangers and panel absorbers?

thanks again for your response. it was very helpful.

 

[VSpaceBoy]

Thanks Steve for the great info!! I too was wondering some of those questions.
Reading your response also raised another question:

How do you know what to use and how much of it? Is there a rule of thumb as to what to use where.

I am in the process of designing my own DIY basement studio and am not sure on where to begin planning materials and such. Would it make more sense to hire you or John to lay something out for me?

SpaceBoy

 

[knightfly]

Acoustic hangers (bass hangers) are custom-fitted to the available space, such as wierd-shaped between-wall areas caused by splaying walls (for flutter echo control and RFZ creation) - They should be hung with heavy picture wire or similar, and should NOT touch anything else including the floor.

The concept is similar to this: say you had a bunch of wide boards suspended in a marina, with small holes drilled all over each board, and all these boards were between you and the main channel of the marina. Now, a boat comes thru the channel and causes a big wake. By the time the wake's ripples get through the several layers of suspended, perforated boards, the water is pretty calm where you're at - because the boards have "sucked up" most of the kinetic energy of the wave before it got to you.

If you think about it, the analogy is really close - The science of "Fluid Dynamics" is the one used for designing airplane wings. Why "fluid"? Because air is just a thin fluid where physics is concerned. They act and react the same in most cases.

One of the more popular ways of building "hangers" is to use Homosote, Celotex, or Sound Board (all the same thing, different names) wrapped in spun glass insulation (the "fluffy stuff") - You can laminate strips of 1/4" plywood across the tops of these with construction adhesive BEFORE wrapping the fluffy insulation around, then drill holes through the "sandwich" of plywood and sound board for hanger wires. The hangers should be far enough apart not to touch firmly, but it shouldn't matter if the fluffy parts lightly brush each other.

"How do you know what to use and how much of it? Is there a rule of thumb as to what to use where.

I am in the process of designing my own DIY basement studio and am not sure on where to begin planning materials and such. Would it make more sense to hire you or John to lay something out for me?" -

You could start by asking your questions at John's site - if things get too involved, John has drawn complete plans for a fee - he also offers phone consultation for less than most phone sex lines.

I'm considering a similar thing, but haven't implemented it yet. John and I will be meeting next month in San Francisco and I hope to discuss it with him at that time.

Meantime, come visit us here

http://johnlsayers.com/phpBB2/index.php

Please spend an hour or so reading through existing threads before posting questions - we've not had much time to set up FAQ's and such, since the site "hit the ground running" - you may find your answers already there, that always makes things easier for us... Steve