Does foam absorb better in the highs?

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Does foam absorb better in the highs?

Postby Bjorn » Sun Jun 23, 2013 7:51 am

I'm having difficulties attenuating the highest frequencies as low as I want to in a room where the reflections are arriving from a sloped ceiling behind the listening position. I'm using rock wool (the right material/density for the job). I've also tried lower density but haven't been able to get all the reflections down below -25 dB which is my minimum goal.

Some mentioned at a forum that they had experienced using a foam product like Auralex attenuated better then porous in the highs. Is this correct and is there any data backing this up? If that's case, I could get som Auralex studiofoam wedges of 2" or similar and place them in front of my rock wool panels. It's above 1kHz I only need better absorption.
http://www.auralex.com/acoustic_studiof ... oam_2w.asp

Also, are the differences between foam products in this area? The Auralex are quite expensive compared to other foam brands.
Why have acoustics been generally overlooked by audiophiles, when they'll worry about things like the purity of the rhodium plating on binding posts?
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Re: Does foam absorb better in the highs?

Postby jhbrandt » Sun Jun 23, 2013 8:35 am

Bjorn,

Are the reflections that you describe Low Frequency? You can use a mirror to locate proper placement for 2" to 4" thick panels. Auralex is fine for 1 kHz and above reflection points. What is your problem specifically? Can you post a drawing?
Cheers,
John
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Re: Does foam absorb better in the highs?

Postby bert stoltenborg » Wed Jun 26, 2013 9:25 am

Bjorn wrote:I'm having difficulties attenuating the highest frequencies as low as I want to in a room where the reflections are arriving from a sloped ceiling behind the listening position. I'm using rock wool (the right material/density for the job). I've also tried lower density but haven't been able to get all the reflections down below -25 dB which is my minimum goal.

Some mentioned at a forum that they had experienced using a foam product like Auralex attenuated better then porous in the highs. Is this correct and is there any data backing this up? If that's case, I could get som Auralex studiofoam wedges of 2" or similar and place them in front of my rock wool panels. It's above 1kHz I only need better absorption.
http://www.auralex.com/acoustic_studiof ... oam_2w.asp

Also, are the differences between foam products in this area? The Auralex are quite expensive compared to other foam brands.


Bjorn,

There is no better material than Rockwool for this. There is a load of measurements on this site about it, just search.
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Re: Does foam absorb better in the highs?

Postby Scott R. Foster » Thu Jun 27, 2013 9:20 am

Get a rug?

It might tie the whole room together.
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Re: Does foam absorb better in the highs?

Postby Bjorn » Thu Jun 27, 2013 11:17 am

bert stoltenborg wrote:
Bjorn wrote:I'm having difficulties attenuating the highest frequencies as low as I want to in a room where the reflections are arriving from a sloped ceiling behind the listening position. I'm using rock wool (the right material/density for the job). I've also tried lower density but haven't been able to get all the reflections down below -25 dB which is my minimum goal.

Some mentioned at a forum that they had experienced using a foam product like Auralex attenuated better then porous in the highs. Is this correct and is there any data backing this up? If that's case, I could get som Auralex studiofoam wedges of 2" or similar and place them in front of my rock wool panels. It's above 1kHz I only need better absorption.
http://www.auralex.com/acoustic_studiof ... oam_2w.asp

Also, are the differences between foam products in this area? The Auralex are quite expensive compared to other foam brands.


Bjorn,

There is no better material than Rockwool for this. There is a load of measurements on this site about it, just search.

Thanks. The one I was referring was able to attenuate highs better with Auralex foam then rockwool. I've no reason to suspect the result was otherwise, he does know how to measure. But maybe that was a one time experience where the wedges on the surface made an improvemen in his spesific case. Hard to say.
Why have acoustics been generally overlooked by audiophiles, when they'll worry about things like the purity of the rhodium plating on binding posts?
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Re: Does foam absorb better in the highs?

Postby jhbrandt » Tue Jul 02, 2013 11:55 am

Bjorn,

Reflection points should have a highly absorptive surface, around 30kg/m3 if you are using rock wool. It is also very important to pick a fabric that performs excellent in this area as well.

Cheers,
John
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Re: Does foam absorb better in the highs?

Postby Scott R. Foster » Tue Jul 02, 2013 12:16 pm

I am serious about the rug. HF deficiency in absorptive treatment is rare because almost everything does a pretty good job on HF.

If you are getting way too much at your listening position I suspect your system EQ [crossover flaw?] is off or you missed a major neat-field reflection point [the floor?].
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Re: Does foam absorb better in the highs?

Postby Bjorn » Tue Jul 02, 2013 9:18 pm

jhbrandt wrote:Bjorn,

Reflection points should have a highly absorptive surface, around 30kg/m3 if you are using rock wool. It is also very important to pick a fabric that performs excellent in this area as well.

Cheers,
John

I could try 30kg/m3. I have it available.

This is the fabric I'm using:
http://www.acoustimac.com/dmd-acoustic-fabric/
I haven't tried any other acoustic fabrics.
Why have acoustics been generally overlooked by audiophiles, when they'll worry about things like the purity of the rhodium plating on binding posts?
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Re: Does foam absorb better in the highs?

Postby Ido » Sat Jul 06, 2013 6:22 pm

from my very subjective experience, no measurements,
nothing comes close to HF absorption of melamine foam. it sucks up all the HF.
wools always get covered, and many "breathing" clothes still reflect back small amounts of HF.
now my honorable dutch brother should kick me in the pants for sounding like all these alchemist sound engineer types....
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Re: Does foam absorb better in the highs?

Postby bert stoltenborg » Sat Jul 06, 2013 10:05 pm

:mrgreen:
Melamine isn't very different from PUR.
It only looks better and cuts nicer, as long as you are not the guy who has to cut it :D
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Re: Does foam absorb better in the highs?

Postby Ido » Sun Jul 07, 2013 8:36 am

PUR is polyur.. ?
honorable brother, in my experience the melamine absorbs more than purr
in the HF.
in most cases this is of no relevance and it won't be noticed, but still...
then again, maybe us 2 lazybones should open up a dumb catalogue and start looking like most people do. not that that would convince me, since my cover has been blown and I'm like these alchemist sound engineers ("I tell you, the sound goes here, then does this summersault, then goes faster where ul get no bass, cause it's shy, and then it spreads out because of the special speakers. science? yea, that's male-female attraction, right? )
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