John Sayers' Recording Studio Design Forum Archive

Ive just got a few questions on a few things that im not understanding with the building of common acoustic absorbers.

Can you use R19 Fiberglass (the fluffy stuff) in place of the Rigid fiberglass? Im guessing you cant, but i would like to know why. I definitely understand space issues but what if you cant get ahold of Rigid Fiberglass?

I also would like more information about spacing the slats on slat resonators. How do you calculate what frequencies it absorbs at what it reflects? Is it best to space the slats based on your room modes?

These might be basic questions, but for some reason i havnt quite been able to understand them.

Thanks,

Typical rigid fiberglas of 3 pounds per square foot is 50 TIMES as dense as standard fluffy batts, so if you've got 300 inches of space for the fluffy stuff you could get similar performance The rigid stuff is made by compressing the regular stuff into "boards", and the sound absorption characteristics are mostly derived from the number of "interstices", or fibers, that the sound needs to get through in order to pass.

Inside a wall, however, you can just slightly overfill the cavities between wallboards so that the insulation presses lightly against the panels, and it works almost as good as the rigid stuff like rockwool and rigid fiberglas.

This does NOT hold true for places where the material is exposed to sound waves directly - here, the fluffy stuff won't even come close.

On the slat resonators, have you been here?

http://www.saecollege.de/reference_mate ... mholtz.xls

As to spacing slats according to room modes, it depends on how bad your modal response is - if you had two identical dimensions, or one that was twice the other, then you might consider doing a specific frequency slat resonator to target that frequency range. Also, in a drum room you'd almost never go wrong by building at least one slat absorber tuned to 300 hZ - that's the basic resonance range of a typical kick drum shell... Steve