# The fluffy pink stuff



## Highside (Jan 4, 2010)

I've been reading more and more of the viability of the regular old fluffy pink stuff as a good base trap. 

What are the typical requirements if one is to use "pink" instead of 703 or mineral wool? Do they need to be as dense or larger. Does it need to be compacted a bit? Etc, etc...

Here's what I've been thinking. I did a search for bass traps several years ago and came across a site (blog, personal page..) where a person made cylindrical traps with the "pink" stuff. I was thinking about going this route so that I could have a pseudo column in the corner that serves as a trap. My idea was to make it look like an SVS cylinder sub.

Could this work or should I just go for super chunks in the corners? 

Will it work if the corner is not completely blocked off since the trap can't truly fit snugly into the corner?


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## Guest (Dec 8, 2011)

What are super chunks?

I think I might have read the same thing. People pretty much using rolls of fiberglass and wrapping them in fabric from wally world. I've also read that fiber glass isn't dense enough to slow down bass waves. IDK what the truth is. I don't think it would cost a whole lot to test it, and if it didn't work, you could just add more fiber glass to your attic.

Could you take before and after REW measurments?


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## bpape (Sep 14, 2006)

What it's really about is gas flow resistivity. As you get thicker in material, the need for higher density decreases - and less dense material can actually work better. 

If you're going to do the cylinder route, just make sure you get enough diameter to make it work low. Think a minimum of a 16" diameter. Bigger is better.

No need to compress the fiberglass. 

What some people will do is to use a denser material like pipe insulation for an outer layer and then fill the core with the fluffy stuff. Gives it a bit more strength.

Bryan


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## typ44q (Apr 7, 2008)

I think what the original post is talking about doing is just using the roll of fiberglass as it comes from the store and wrapping it in cloth so there would be no core, it would be a solid roll of fiberglass making it fairly dense.
I have read this as well and would love to see some actual measurements.


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## bpape (Sep 14, 2006)

Sure. That can work. I guess my point is that the same amount of fiberglass, undone from the package and allowed to 'fluff up' a bit and become a larger diameter would perform even lower.

Bryan


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## eugovector (Sep 4, 2006)

Generic said:


> What are super chunks?
> 
> I think I might have read the same thing. People pretty much using rolls of fiberglass and wrapping them in fabric from wally world. I've also read that fiber glass isn't dense enough to slow down bass waves. IDK what the truth is. I don't think it would cost a whole lot to test it, and if it didn't work, you could just add more fiber glass to your attic.
> 
> Could you take before and after REW measurments?


Superchunks= http://forum.studiotips.com/viewtopic.php?t=535


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## Highside (Jan 4, 2010)

bpape said:


> If you're going to do the cylinder route, just make sure you get enough diameter to make it work low. Think a minimum of a 16" diameter. Bigger is better.


The initial idea was to make them 20" in diameter but it may stick out a bit too far. If I go ahead a do this I will at least try for 16-18".

I may not take them all the way to the ceiling though. Is there going to be a big loss in benefit if I only make them say 48-54" high?


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## bpape (Sep 14, 2006)

The less height you have, the less overall surface area. How much the impact will be will depend on what and how much the room requires and how much other you have in the room over the various portions of the spectrum.

Bryan


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## Highside (Jan 4, 2010)

bpape said:


> What some people will do is to use a denser material like pipe insulation for an outer layer and then fill the core with the fluffy stuff. Gives it a bit more strength.


I see the process here now after a little more research for "tube" traps.

The John Risch method does not include any pink fluffy inside of the pipe insulation. Can I assume that adding the fluffy will give more benefit based on your explanation of using/creating a more dense material?


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## bpape (Sep 14, 2006)

Jon's stuff is OK but not all that wonderful quite honestly. Some of his 'designs' show a serious lack of understanding about acoustics and room treatments. Enough about that.

Yes - filling the tube is only going to help how low the absorber will effectively treat.

Bryan


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## Highside (Jan 4, 2010)

bpape said:


> Jon's stuff is OK but not all that wonderful quite honestly. Some of his 'designs' show a serious lack of understanding about acoustics and room treatments. Enough about that.


If John's methods are not all that wonderful, where is his shortfall? Sticking with the tube design for the time being, how and where would I make up that up, if I still want a tube/column?

Sorry, I'm sounding so redundant here...


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## bpape (Sep 14, 2006)

You're fine. The thinner shell and larger diameter without filling can cause humps in the curves as well as miss in the lower frequencies.

His diffusion designs show a lack of fundamental understanding of what diffusion is. They'll scatter but they don't diffuse. A diffuser scatters randomly and evenly both in space and in time which his don't.

Some of the others, well, they work kind of for some types of speakers but not for most.

Do the 1" or 2" wall tube and fill with fluffy insulation. If you want control over higher frequency absorption, get it with the facing on it, and pull it off 1/2 of the surface so it can be rotated to be fully absorptive at higher frequencies, reflective at higher frequencies, or a combination at different angles.

Bryan


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## SAC (Dec 3, 2009)

Highside said:


> If John's methods are not all that wonderful, where is his shortfall? Sticking with the tube design for the time being, how and where would I make up that up, if I still want a tube/column?
> 
> Sorry, I'm sounding so redundant here...


Brian is correct.

Part of the problem that you are encountering in your proposal is that you are confusing pressure based tuned resonate absorbers with velocity based porous absorbers.

Simply picking and choosing various aspects of each and combining them randomly is not the process to obtain optimal performance.

Making a 'small' diameter tube trap filled with porous material will do little - and the correspondence between whatever frequency to which the pipe is tuned and that which is measured to be a problematic frequency in the particular room you are in will be serendipitous at best - and it will probably not be distributed in the place the trap is located! And such a small porous trap will be of little use if the porous material is contained within a reflective shell. In other words, what unfortunately results is the worst of both worlds!

In order to proceed much further I would suggest spending a bit of time to further investigate the behavioral principles of both pressure based resonant absorber design and velocity based porous absorber design. You can wander about the web trying to find such information (and sorting through the tons of erroneous information) or you might simply access the library and reference the source text _Acoustic Absorbers and Diffusors_ by D'Antonio & Cox.


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## Highside (Jan 4, 2010)

SAC said:


> In order to proceed much further I would suggest spending a bit of time to further investigate the behavioral principles of both pressure based resonant absorber design and velocity based porous absorber design. You can wander about the web trying to find such information (and sorting through the tons of erroneous information) or you might simply access the library and reference the source text _Acoustic Absorbers and Diffusors_ by D'Antonio & Cox.


O....K.....:rofl:

Could you talk further over my head please.:dumbcrazy:


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## bpape (Sep 14, 2006)

The 'tube' type traps when made from a porous material are not truly pressure type absorbers. Pressure absorbers use a sealed cavity of air to act like a spring and provide resistance to movement. The mass of the front and the depth of the cavity determine the tuning.

What you're looking at doing is not a pressure absorber since the entire tube shell allows air to pass in and our freely so there's no way for the air to ever act like a spring. 

Bryan


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