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30 PPI foam for HOM absorption in waveguides

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JLH

JLH

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Joined 2005
#1
I was looking for sources of 30 PPI open cell foam to experiment with. The problem I found is few places sell it in thicknesses required to fill most waveguides. I really don’t like the idea of layering sections of foam to get the required depth. I did contact one place that was willing to order it from the manufacturer in thicker pieces. However, cost would be a problem unless a group buy is used. Is there any interest in getting a group buy for foam?

Right now it looks like 8” cubes can be bought for $16 each if a minimum of 25 are ordered. So, if we get people to buy in pairs, then we need at least 12 people with one person buying 3 cubes. I think $36 for a pair of 8” cubes was pretty reasonable. Size tolerance is +/- 0.25”.

12” cubes would run $67 a piece if a minimum of 9 are ordered. I thought that might be a bit rich for most people, so I did not pursue it.
Let me know if you are interested by replying to this thread. We have until the end of October to get the required numbers.

Rgs, JLH
 
#3
Very nice work Patrick. I used to run Image Dynamics HLCDs in my truck. Back in the late 80's and early 90's I competed in sound offs and won a few shows. It was a fun time, but I'm a family man now and have settled for home audio only.

I too found the foam you mention at McMaster Carr. I just really want to avoid making layers. I would like one solid and continious piece of foam. Right now it looks like there is a lack of interest in these 8" cubes. If I don't get enough people interested, then I'll have to go it alone.

Rgs, JLH
 
#4
JLH said:
Right now it looks like 8” cubes can be bought for $16 each if a minimum of 25 are ordered. So, if we get people to buy in pairs, then we need at least 12 people with one person buying 3 cubes. I think $36 for a pair of 8” cubes was pretty reasonable. Size tolerance is +/- 0.25”.

12” cubes would run $67 a piece if a minimum of 9 are ordered.
Click to expand...

My experience is that the most important area to cover is the first few inches from the phase plug of the horn. An 8" cube should do the trick for the large majority of applications. The hardest part is finding a good way to shape it cleanly. Earl uses a hot wire. I hacked away at it with a sharp knife, then final trim with scissors. That works okay for one offs.

Sheldon
 
#5
I too found the foam you mention at McMaster Carr. I just really want to avoid making layers. I would like one solid and continious piece of foam. Right now it looks like there is a lack of interest in these 8" cubes. If I don't get enough people interested, then I'll have to go it alone.
Click to expand...

I bought some @30 ppi foam from a foam shop in nice thicknesses at a decent price. He was selling it to pond owners for their filters. So you might inquire at a local fish pond supply house
 
#6
I'm interested in getting foam, too. However, I'll be starting with filling 12" round waveguides so 8" cubes won't be quite wide enough. I guess I'd need sheets I could cut out and layer.

The McMaster Carr site confused me a little. I see "psi" specifications, but no "ppi" specs. I think "ppi" refers to pours per inch and not pounds per square inch. Would Patrick or anyone else please post a specific part number for foam that works on HOMs?
 
#8
TrickMcKaha said:
I'm interested in getting foam, too. However, I'll be starting with filling 12" round waveguides so 8" cubes won't be quite wide enough. I guess I'd need sheets I could cut out and layer.

The McMaster Carr site confused me a little. I see "psi" specifications, but no "ppi" specs. I think "ppi" refers to pours per inch and not pounds per square inch. Would Patrick or anyone else please post a specific part number for foam that works on HOMs?
Click to expand...

Here's what I'm using

http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-12.html#post1245342

Note that the "solid" pieces used by Geddes are superior.
 
#11
Ed LaFontaine said:
Any of you gentlemen have leftovers?

My application is a pair of QSC 152 waveguides.
Click to expand...

Do you have a build thread? I would love to follow since I have built a set of QSC 152 clones already but Im always looking to learn something.

I have used the 30 ppi foam from swisstropics.com (link just posted) but I can not seem to figure out what it really does to the sound or the measurements. I had limited luck with it.

I wonder what Geddes really uses??
 
#12
Geddes is in the greater Detroit area. I would speculate he uses a local source. 😕 He has graciously offered to sell some. However, my labor is cheaper than his. 😉

I like the source JLH has posted. Thanks. :cheers:
I'll look into making a plug from 2 pieces. One for the throat, beginning with a cube. The piece outside of that will be made from flat stock. I'll prepare templates for the x & y axis of the wg and remove material in "sections".
For retention of the pieces, I'll investigate copper wire inserted into the walls of the guide. I haven't determined the gauge or length yet (but my thoughts are ~24 gauge and 1/2" exposure). The wire will be bent over to serve as barbs, and be distributed around the guide.

For reference, here are other links.

Reticulated Foam - Stephenson & Lawyer - Foam Fabrication for Engineered Applications

RETICULATED FOAM SHEETS - H-O Products Corp.

Welcome to Foam Factory

Dryfast Foam, Outdoor Foams, Patio Furniture Custom Cushion Replacement, Hi-Flow Foam
 
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