studiotips question..

[victoryaloy]

at the top of the acoustics section it says:
"A resonant panel or diaphragmatic absorber is used to absorb low frequencies."
"The simple way to build a resonant absorber is to mount panel on a 2 by 4 frame with fiberglass batt (R11) or 703 inside of it."

I dont understand how R11 can be the same as 703.

any ideas?

[DanDan]

Some ideas-
www.bobgolds.com Actual absorption coefficients, although not in a box.
The panel absorber may be best explained the the original BBC design and research document. Google BBC and LF modular membrane absorber, or something like that.
In such enclosed systems, a stud wall being another, the fibre may be viewed at least partly as a damper to prevent resonance building up. It is absorbtion but not as we know it Jim. This can mean that light materials can outperform (or equal) the denser ones.
DD

[victoryaloy]

Originally Posted by DanDan

Some ideas-
www.bobgolds.com Actual absorption coefficients, although not in a box.
The panel absorber may be best explained the the original BBC design and research document. Google BBC and LF modular membrane absorber, or something like that.
In such enclosed systems, a stud wall being another, the fibre may be viewed at least partly as a damper to prevent resonance building up. It is absorbtion but not as we know it Jim. This can mean that light materials can outperform (or equal) the denser ones.
DD

i see.. so there is more to it than a "2 by 4 frame with fiberglass batt (R11)" will be the same as 703!

[avare]

Adding confusion to what Dan wrote, the other main effect of the material is cause the sound waves to develop isothermally instead of adiabatically. The net effect of this is that sound travels 18% faster in air than in the absorbent material.

The physicists in the crowd will recognize that 1.18 is the square root of the ratio of specific heats of air for constant volume vs. constant pressure.

Aspirin, the drug of choice for learning acoustics,

Andre

[Weasel9992]

Originally Posted by avare

Adding confusion to what Dan wrote, the other main effect of the material is cThe physicists in the crowd will recognize that 1.18 is the square root of the ratio of specific heats of air for constant volume vs. constant pressure.

Well, yeah. Duh.

Frank