Fiber that is lightweight (10 - 15kg/m3) or that has low gas-flow resistivity is STILL reflective after a certain depth.
The following is some of my analysis of fiber trapping from 8" (200 mm) to 16" (405 mm) deep.
8" deep is good down to 160 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 120Hz. [-6 dB @ 200 Hz]
10" deep is good down to 130 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 94Hz. [-6 dB @ 180 Hz]
12" deep is good down to 120 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 90Hz. [-6 dB @ 190 Hz]
14" deep is good down to 110 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 77Hz. [-6 dB @ 230 Hz]
16" deep is good down to 110 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 70Hz. [-6 dB @ 290 Hz]
The last entry in [-6 dB] is VERY interesting and should be noted!!
The best absorber will attenuate sound @ -10 dB per surface contact but few absorbers attain to AbsCo 0.999 or 1.0. Most absorbers will be doing very well if they get A.C. 0.8. that means an attenuation of -6 dB per surface contact from the sound balloon/wave.
I think that being conservative when calculating the absorption of products is more realistic.
That said, fiber trapping is not going to do for LF trapping and control. Period. So, we're left with limp pressure trapping and tuned trapping...
The following is some of my analysis of fiber trapping from 8" (200 mm) to 16" (405 mm) deep.
8" deep is good down to 160 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 120Hz. [-6 dB @ 200 Hz]
10" deep is good down to 130 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 94Hz. [-6 dB @ 180 Hz]
12" deep is good down to 120 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 90Hz. [-6 dB @ 190 Hz]
14" deep is good down to 110 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 77Hz. [-6 dB @ 230 Hz]
16" deep is good down to 110 Hz (4.5 dB of attenuation). The -3 dB Cutoff is 70Hz. [-6 dB @ 290 Hz]
The last entry in [-6 dB] is VERY interesting and should be noted!!
The best absorber will attenuate sound @ -10 dB per surface contact but few absorbers attain to AbsCo 0.999 or 1.0. Most absorbers will be doing very well if they get A.C. 0.8. that means an attenuation of -6 dB per surface contact from the sound balloon/wave.
I think that being conservative when calculating the absorption of products is more realistic.
That said, fiber trapping is not going to do for LF trapping and control. Period. So, we're left with limp pressure trapping and tuned trapping...
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