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Old 21st July 2015, 06:49 PM   #1
jeshi is offline jeshi  Japan
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Default EVA foam for performance speaker enclosures

I was very inspired by xrk971's thread Foam Core Board Speaker Enclosures?

When that thread started it was aiming at low cost, rapid building as the motivation for using foam. But it occurred to me that the right foam might actually be a better building material than wood for speaker enclosure. Wood is inherently a resonant material; it is used for musical instruments because of it resonant nature. Foam on the other hand is often used for soundproofing. Hit a piece of wood and it makes a medium to high pitched resonant sound. Hit a piece of foam and it sounds dead. As wood get denser, the sound it makes rises in pitch.

The Celestion SL600 and 6000 speakers from the 1980's also used a very different thinking for the enclosure. These speakers used a lightweight aluminum honeycomb material called aerolam.
Celestion System 6000 loudspeaker system | Stereophile.com

Celestion SL600si loudspeaker & DLP600 digital equalizer | Stereophile.com
And quoting from that article

The cabinet is unique to the SL600Si (and similar to the SL700) in being fabricated from a 0.5"-thick, metal-honeycomb aircraft flooring material. While low in mass, thus minimizing energy storage, it is sufficiently stiff enough for the resonances of its panels to be pushed almost two octaves higher in frequency than with a conventional wooden cabinet. The contribution to the overall sound from the flexing of the enclosure walls will thus be moved away from the region where instruments and voices have their energy maxima, and will also be lower in level. The result should be a low delayed-resonance signature, with correspondingly low levels of midrange coloration. Because the walls of the enclosure will now be virtually transparent to midrange sound, it is filled with carefully graded foam to absorb as much of the woofer's backwave as possible.
I always thought that celestion was onto something here with: low mass, low energy storage, and shifting the wall resonance away from the midrange.

Also when we build speaker enclosures out of wood, we have to line the walls to damp reflections, and fill the box to absorb the sound (make it non-transparent), and we have to add bracing and mass to the wood walls to damp resonance and vibrations. We have to apply all of these technique to compensate for the fact that wood is a resonant material with a pitch often in the middle-to-high-band frequencies.

As I looked around at different foams I realized that the ideal speaker enclosure material might be
- low mass
- semi-ridging / semi-flexible to have a low resonance frequency
- low energy storage
- sound absorbing (non-reflective)
- vibration absorbing
- and with a low resonant frequency (since a perfect sound absorber does not exist)

I found a foam called EVA which appears to have all these properties.
EVA Foam | popular Closed Cell Foam
  • Impact and vibration absorption
  • Acoustic and thermal insulation properties
  • Buoyancy with low water absorption
  • Suitability for thermo-forming and thermo-moulding
EVA is also very easy to work with. It is one of the main materials used in costume building because of it's easy workability. Exacto knifes, glues, and heat guns allow for easy shaping into any form (curves, domes, facets...)
Creating a Costume/Cosplay from E.V.A Foam : EVA Foam & The Differnt Types Youll Use.
And EVA can be wet or dry sanded to create smooth surfaces, bevels, waveguides..
EVA foam also laminates very well to create thick panels. And I believe that the laminated EVA, with the multiple boundary layers, may have additional benefits.

I am posting this in the fullrange section because I think the fullrange crowd is open minded to experimentation, but I believe from my builds so far that EVA foam works just as well in multi-way designs.

I have two builds currently using EVA foam. A full-range sealed box with an FF105wk driver, and a 2way high-end build using a Satori MW16 and RS28f tweeter with a custom shaped waveguide and an LR2 crossover. I will be posting more details about these builds and my building techniques.
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Old 21st July 2015, 07:19 PM   #2
timpert is offline timpert  Netherlands
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I am very curious about what you have made with it. Such a good material deserves a nicer application than those hideous Crocs. Pictures please!
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Old 21st July 2015, 07:24 PM   #3
xrk971 is offline xrk971  United States
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Great idea to use foam specifically to make a higher performance speaker than one made of wood! It's a bonus that it can be made on a kitchen table with a razor and glue gun. Looking forward to seeing your speakers, especially the waveguide for the RS28F! Maybe EVA foam combined with certain 3d printed parts can result in even a better speaker?
Thanks for starting this thread.
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Old 21st July 2015, 07:40 PM   #4
jeshi is offline jeshi  Japan
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My first build to test the material and develop my building techniques was a sealed box full-range speaker using a single fostex FF105wk driver.
Because I wanted to develop my building skills I decided to go for a very complex shape. I designed a truncated pyramid, with a sloped front baffle, no parallel walls and a curved top. This would minimize all internal reflections (prevent standing waves). And because of the sound absorption abilities of EVA I didn't bother with lining the walls.

I built it with 10mm EVA foam sold in Japan as LionBoard

The front baffle is made from two sheets laminated together to form a 20mm panel. I have an internal bracing "pillar" running horizontal to control resonance on the side walls (walls only 10mm thick) and I stuffed with long fiber loose wool.

The CSD waterfall plots also look good and comparable to my focal CMS40 monitors. I think most of the resonance is from the FF105 driver. I want to try a higher quality full-range in the near future. I show both a no-eq and full-eq version.
The FF105wk is known for having a strong 7khz resonance spike, but it is not as strong on my speaker which may be due to the EVA foam's vibration damping ability.
Attached Images
File Type: jpg ff105wk sealed-box no eq.jpg (76.7 KB, 560 views)
File Type: jpg ff105-eva-csd-no-eq.jpg (147.9 KB, 549 views)
File Type: jpg ff105-eva-csd-full-eq.jpg (127.6 KB, 542 views)
File Type: jpg focal cms40 csd.jpg (118.1 KB, 537 views)
File Type: jpg P1110212.jpg (274.5 KB, 543 views)
File Type: jpg P1110213.jpg (242.6 KB, 187 views)
File Type: jpg P1110214.jpg (209.2 KB, 174 views)
File Type: jpg P1110215.jpg (259.8 KB, 157 views)
File Type: jpg ff105wk sealed-box full eq.jpg (76.2 KB, 136 views)

Last edited by jeshi; 21st July 2015 at 08:09 PM.
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Old 21st July 2015, 08:16 PM   #5
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Is this the same stuff?

Depron and EPP Foam Suppliers, Carbon Fiber Sheets, Carbon Rods and Tubes, RC Model Airplane Engines, Lipo Batteries
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Old 21st July 2015, 08:34 PM   #6
jeshi is offline jeshi  Japan
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no sorry that is a polystyrene foam
Depron Sheets

EVA is a flexible foam. In America I think EVA is mostly colored or black. I think the white EVA is more a Japanese version (Lion Board, koyo softboard).

check out this link which lists places where you can buy or find EVA
Creating a Costume/Cosplay from E.V.A Foam : EVA Foam & The Differnt Types Youll Use
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Old 21st July 2015, 08:45 PM   #7
jeshi is offline jeshi  Japan
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Here are some on amazon. They are mostly sold in floor tile packs or in craft packs. The craft packs are often multi-colored since the purpose is to have the colors.

Amazon.com: eva foam

The black EVA tiles could make for a nice looking enclosure.

Here is a nice one being sold for a weight room to absorb people dropping barbells. 12 tiles each 12" x 12" x 1/2" for ~$13
http://www.amazon.com/Cap-Barbell-12...words=eva+foam

And here is a roll version 48" x 96"
http://www.amazon.com/Anti-Fatigue-F...words=eva+foam

And here are some 1" thick 2' x 2' tiles. But the prices goes up. This is why I tend to buy the 10mm (1/2") style and then glue laminate them to get 20mm, 30mm.... But this particular pack is not bad. 16square feet of 1" thick for $43
http://www.amazon.com/Exervo-Thick-P...words=eva+foam

Last edited by jeshi; 21st July 2015 at 09:04 PM.
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Old 21st July 2015, 09:33 PM   #8
Squeak is offline Squeak  Denmark
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A small low power cab is one thing and pretty simple. Another thing entirely is to do a big cab with larger spans of material.

Either you'll have to brace it a lot or you'll have to double or triple the materiel.
Either way you'll end up with a cab that is a lot bigger for the same volume.

Maybe a sandwich material with dense cardboard some millimeters thick? The sudden change in accoustic properties from layer to layer alone, will have a damping effect on higher frequencies.

Curving the foam in one or two directions will also help a lot. But isn't always practical or desirable.

Last edited by Squeak; 21st July 2015 at 09:44 PM.
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Old 21st July 2015, 09:53 PM   #9
jeshi is offline jeshi  Japan
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Quote:
Originally Posted by Squeak View Post
A small low power cab is one thing and pretty simple. Another thing entirely is to do a big cab with larger spans of material.

Either you'll have to brace it a lot or you'll have to double or triple the materiel.
Either way you'll end up with a cab that is a lot bigger for the same volume.

Maybe a sandwich material with dense cardboard some millimeters thick? The sudden change in accoustic properties from layer to layer alone, will have a damping effect on higher frequencies.

Curving the foam in one or two directions will also help a lot. But isn't always practical or desirable.
I agree in theory this is what one would think, but so far it is appearing from my tests that floppy EVA panels might actually absorb the sound and don't resonate it out, maybe in a similar way to how a limp-membrane bass trap vibrates to absorb sound. I am still experimenting with this material and different approaches. My satori speaker has 330mm x 200mm x20mm side panels and a 6.5" driver going down to 45hz, so that I think classifies outside of a "small low power cab" application.

And yes when I say laminate, I mean multiple sheets of EVA glued together rubber contact cement (like a sandwich), and this is what I meant by boundary layers. The EVA naturally absorbs high frequencies and even a simple 10mm sheet absorbs middle and high frequencies. I have some test experiments on the material which I will post up in the next couple days.

Last edited by jeshi; 21st July 2015 at 09:59 PM.
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Old 21st July 2015, 10:14 PM   #10
Squeak is offline Squeak  Denmark
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Looking very much forward to it. This could really be a revolution in DIY speakers, or maybe speakers in general.
I'm sure you have come across the other examples of using PVA before? Like the Smith horn prototype.
I too have been toying with the stuff for doing lightweight back horns to hang from the ceiling, but gave up. Perhaps too early?
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