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darkbuddha
#1
4th January 2012
4th January 2012
#1
Gear maniac

Joined: Nov 2011
Location: Sarasota, FL USA
Posts: 174

Any thoughts on these results from the Porous Absorber Calculator?

So after doing a bunch of reading about GFRs the last few days, I got to playing around with the Porous Absorber Calculator. I thought about the materials I had available to me, my space limitations, and build complexity and decided there were a few different absorber layering combination possibilities that would meet my requirement of maximum of 6-6.5" of depth (including air gaps). Here's what I got... note the frequency range has been limited to 40-500Hz (the range giving me problems)...

Porous Absorber Calculator - Results

I found the differences of having the air gap between the panels interesting, so I also compared changing which material was on top...

Porous Absorber Calculator - Results

Do note, these calculations were done using a GFR of 16000 for the OC703 (per OC) and 14000 for the SAFB (estimation for 2.5pcf density). All other parameters were left untouched.

Thoughts?
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Composer, researcher, educator
#2
4th January 2012
4th January 2012
#2
Lives for gear

Joined: May 2011
Location: Phoenix, AZ
Posts: 1,269

I'm not sure how indepth this program works, but my understanding is that the problem with using different density materials in a single panel is that it will cause yet another unnecessary chain of reflection. When looking at absorption coefficients, everything that is not absorbed is reflected/diffused correct? So you're actually creating more reflective surface area than your original room had. But also still more absorption..I could be completely wrong on this. However, if you want to build them, test it, and give us results, by all means!

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#3
4th January 2012
4th January 2012
#3
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,967

OC703 the real GFR

NASA reckon 703 has a GFR of 27000.
Looking around at other GFRs I find this figure more credible than OC's.
DD
darkbuddha
#4
4th January 2012
4th January 2012
#4
Gear maniac

Joined: Nov 2011
Location: Sarasota, FL USA
Posts: 174

Quote:
Originally Posted by DanDan
NASA reckon 703 has a GFR of 27000.
Looking around at other GFRs I find this figure more credible than OC's.
DD
Thoughts on my estimate for the GFR for 2.5pcf mineral wool?
#5
4th January 2012
4th January 2012
#5
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,967

Guesses

These calculators are fun but have limitations.
e.g. What happens when a fairly rigid panel straddles a corner?
Apart from the location benefits, I believe a partly resonant effect kicks in.
So straddling panels of 100KG material can have greatly enhanced behaviour.
Try some other angles of incidence for interest.
The practical decision remains the same. If you have the space the best fibre traps are very deep and use light cheap fibre. If you are stuck for space, the dense panels, particularly with FRK added, become very useful.
DD
darkbuddha
#6
4th January 2012
4th January 2012
#6
Gear maniac

Joined: Nov 2011
Location: Sarasota, FL USA
Posts: 174

They are fun, and hopefully helpful. I will certainly try some different angles and see what I get. What I'm looking for is something to help loosely predict the general effective range of an absorber that matches my needs, versus just building an absorber I hope works. Unfortunately, given my space limitations, I simply don't have room for deep (low density) absorbers on the walls. I have done some pink fluffy filled stuff already... a 15x18x96" vertical corner soffit, two 12x24x30" box soffits (over bookcases), and two 15x12x19x66" mini-chunk traps, and plan to do two more 6x12x96" vertical corner soffits. The rest of the space dictates stuff limited to 3-6" in depth.

I will retest the space again after I finish the last of the vertical corner soffits and see where it's at. Then hopefully I can use the PAC to really help guide me on what other absorbers I'll build.
#7
4th January 2012
4th January 2012
#7
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,967

Shallow

3-6 inches use dense material. Availability and cost will decide which one.
Would you consider an enhanced LF design. A couple of GS have achieved amazing results with VPR ish designs, some only 4 inches thick.
My Experiment with a Metal Panel Absorber
DD
darkbuddha
#8
4th January 2012
4th January 2012
#8
Gear maniac

Joined: Nov 2011
Location: Sarasota, FL USA
Posts: 174

Thanks... I will definitely keep that in mind if my room doesn't start shaping up. BTW, I've already sourced 16 panels of 1.5" OC703 and 16 panels of 3" 2.5pcf Thermafiber SAFB, now I'm just looking for the most cost and performance effective usage that I can get from them.

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