eggcrate foam specs?what do they mean?

[mclsound]

properties
-2 inch thickness
-2lbs/cu ft. density
open cell design

freq------NRC
125hz----0.18
250hz----0.32
500hz----0.92
1000hz---1.06
2000hz---0.93
4000hz---0.92

NRC rating 0.80

My question is if this product is good for a cabinet lining housing 2-12"AT for 20-200hz and a Volt 12 for 200-800hz
thanks john

[macboy]

NRC = Noise Reduction Coefficient.

simplified:
0 is "completely" reflective, no absorption.
1 is "completely" absorptive, no reflection.
testing methodology can result in >1 numbers.

The overall NRC is an average over a limited frequency range (250 to 2000 I think, essentially covering speech frequencies only).

If the sound is subject to bouncing off the material several times, such as within an air duct, or within a speaker cabinet, or in a small room, then the effective absorption is magnified due to the multiple opportunities to absorb the sound energy.

[mondogenerator]

in not entirely sure how its possible to have an absorption coefficient with a number greater than 1......see the 1khz ....1.06? really?

i wouldn't be totally sure about the published specs.

[mondogenerator]

Originally Posted by macboy

NRC = Noise Reduction Coefficient.

testing methodology *snip*will always(unless measuring accuracy is bad)*snip* result in <1 numbers.

lol why beat about the bush.....!

specs are a bit dodgy if you ask me

[macboy]

The only thing clearly dodgy here is the uniformed opinions being expressed. (that said I can't vouch for the specs of this material, but there is nothing here to suggest anything dodgy about them).

The NRC specs for many materials are >1 at certain frequencies. This is due to the way the test is done, and is considered an acceptable result. This is because the number is not based on a single reflection, but rather, the attenuation after several reflections. The test is done in a special reverberation room, and the NRC number is related to the time it takes for the tone at the specified frequency to die down. Obviously any frequency will decay to nil after some time, but if the sound decays to a certain (small) level after a specified (small) amount of time, it can score a 1.00. If it decays even faster than that, then it can score better than 1. If it takes longer, it scores less than 1. Look up ASTM C423 if you want the gory details.

[speaker dave]

Originally Posted by mclsound

properties
-2 inch thickness
-2lbs/cu ft. density
open cell design

freq------NRC
125hz----0.18
250hz----0.32
500hz----0.92
1000hz---1.06
2000hz---0.93
4000hz---0.92

NRC rating 0.80

My question is if this product is good for a cabinet lining housing 2-12"AT for 20-200hz and a Volt 12 for 200-800hz
thanks john

The answer is: not so good, at least for the 20 to 200 range. You would want a higer absorption at 125 and 250. It is hard to beat good old fiberglass, but you need some thickness and the efficiency of the material will increase if you can get it off the surface.

David S.

[mclsound]

thanks guys
so what I gather here is that this stuff covered with grill cloth would work better in the livingroom than the cabinet?
I thought it would absorb more mid/hi frequencies than 20-200hz in the cabinet?
Or do I have it backwards?

[speaker dave]

It will absorb more mids and highs. By your specs the material is a good absorber from 500 Hz up (.9 or higher).

Low frequencies are always difficult to absorb. The lower you want to absorb the thicker the material needs to be. In general you need material of a depth of about 1/6 the wavelength for good absorption.

David S.

[mclsound]

Now are we not trying to eliminate the upper frequencies in the bass cabinet?
Are you saying 5 inch roxul would be better?
I am confused as to what we are doing in this cabinet?
Maybe i need an explanation.
thanks

[mondogenerator]

Originally Posted by macboy

The only thing clearly dodgy here is the uniformed opinions being expressed. (that said I can't vouch for the specs of this material, but there is nothing here to suggest anything dodgy about them).

The NRC specs for many materials are >1 at certain frequencies. This is due to the way the test is done, and is considered an acceptable result. This is because the number is not based on a single reflection, but rather, the attenuation after several reflections. The test is done in a special reverberation room, and the NRC number is related to the time it takes for the tone at the specified frequency to die down. Obviously any frequency will decay to nil after some time, but if the sound decays to a certain (small) level after a specified (small) amount of time, it can score a 1.00. If it decays even faster than that, then it can score better than 1. If it takes longer, it scores less than 1. Look up ASTM C423 if you want the gory details.

i consider myself told

but seriously then, is this not the same coeffiecient used in architechural acoustics? forgive me i might be totally misinformed/confused about something, but is there another absorption standard? it just im sure i recall stumbling on a page with various materials as a comparison but perhaps a different metric?