Polyurethane Foam 2, 6, 8 inch Thick - Graphic Absorption Coefficients in Octave

Hi to everyone!

I have been searching the Absorber Coeficient in Octaves Chart for the Spray Polyurethane Foam in thickness of 2, 6 and 8 inches(5.08, 15.24 and 20.32 Centimeters respectively!) and found NOTHING. All I found is a chart for Spray Polyurethane but the thickness is Lower than I need to know!!.

I need this Chart in order to add to the EASE MATERIAL DATA  BASE for a better simulation in a study of acoustics in a very large room with this material applyed inside the roof.

Do someone have or know where I could find these data chart in Octaves?

Thanks a lot for any comments,
Opacheco.

I don't know where, but if you have some samples of the material, let's say 1m^2 of each you could measure using your bathroom, a speaker and a microphone, it doesn't need to be a reference mic but it could help. If you do it is good to have some samples of some other material that you have the absorber coeficient and take it as reference, to know how exactly they are. Sure better than any guess you could made.

I found this that could help for 45mm
Hz        125        250      500    1K      2K      4K               
alpha  0.15        0.7      1.0    0.85  0.91    0.9             

That 1.0 at 1kHz is probably because some resonation in the config the measurements where made, made you own...

First of all go and do all you need to do in the bathrrom before starting so you don't need to stop your measuring.
Then put your speaker in a corner to excite the room, in the middle of the room put your mic.
Measure RT60 (RT30 will work, in fact is what you'll be using, hard to get 60dB over noise floor) of your bathroom empty, take out any curtains and towels to get higher values and better results. You can use REW soft or any other that gives you the RT60 in octave bands.
Take the values for future use.
Measure your room's RT60 with your reference material (same for the other materials) inside (not critical where but you could move it around and do a couple of measuring for better results, it's critical that if you want to know the alpha of the material stick to the wall do it with the material just resting on a wall or floor, if you want the alpha 2 inch from wall measure them 2 inch from the wall.

Now you have RT60 of your room with and without your samples.

Now:
A0=0.162*V/Tr0
being:
A0= total absorption
Tr0=RT60 of empty room
V= Room's volume

Then a0=A0/S
a0 the average alpha of the room
S is room surface

At last:
Tr1=0.162*V/{(S-S1)*a0+S1*a1}
where Tr1 is the time with the sample inside
S1 is the surface of the sample of absorbent
and our preciated a1 is the alpha of our material

The math should be done for each freq separately and using each frec time will give each frec coeficient... this excel should help here, it was made in google docs so opening it with it shouldn't bring trouble. Extension is .xlsx not .doc, I added .doc to upload it here, change it.

For reference, samp 1 is a material I'm developing and sample 2 is a comercial 35mm absorbent.


JS

PD: This shouldn't be here, in the chamber maybe or studio A... just saying.

joaquins,

I understand everything you say!!....let me to check for tha possibillity of this measurement experiment but like last option because now I think to use the Physic Department of University in my City(by the way; this acoustics design work is for this University in a new built hall!!) for do a couple of Kundt Tube Measurements of Polyurethane samples.


Thanks for this interesting idea!
Opacheco.

Kundt Tube is harder to do at home, that's why I said bathroom... (rev chamber)
Kundt Tube is also more limited technique than the chamber, not if using the bath as chamber, but a real chamber is better in some ways...

JS