EVA foam for performance speaker enclosures

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

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[/FONT]
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
intecfoams UK EVA
  • 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.

Some preliminary panel property testing. I will explore this more in the future once I can build a better testing apparatus.
Panel resonance tests:
http://www.diyaudio.com/forums/full...rmance-speaker-enclosures-16.html#post4456901

Panel transmission tests:
http://www.diyaudio.com/forums/full...rmance-speaker-enclosures-24.html#post4467017

Mattes flower speakers : OB fullrange using high density EVA foam for flower shaped baffles (shared by user Mattes, Oct 2018)
full range flower
with the 18" bass flower
My first flower petals experiment



I also started a thread on my multi-way experiments with EVA foam speakers over here OB compact 3way nearfield monitor
 
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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.
 
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.
 

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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
 
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-1...=UTF8&qid=1437511756&sr=8-4&keywords=eva+foam

And here is a roll version 48" x 96"
http://www.amazon.com/Anti-Fatigue-...UTF8&qid=1437511950&sr=8-17&keywords=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-...UTF8&qid=1437512332&sr=8-24&keywords=eva+foam
 
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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.
 
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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.
 
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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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yes I was thinking something similar, that a mix of foam materials might complement each other. I am still not sure if EVA would be the best material for a sealed sub-woofer type cabinet (10" 12" drivers) for example, but so far EVA looks happy with 6.5" drivers. But a sub cab might be worth trying at some point as an experiment. I do think EVA would be great for an open-baffle dipole subwoofer for the driver mounting baffles (vibration damping).

I am not sure this will be a revolution, but it might at least open up some more experimentation in mixed materials. I think the current thinking of using multiple different materials (wood, bracing with mass-loaded layers, felt walls, and stuffing) basically works to control and absorb the sound and vibrations in a speaker enclosure at different frequencies. Foam wall material might be just another valid but different approach that can achieve a similar level of performance.
 
Foam, if as good or better than wood (of any kind), as a valid material would clearly be a revolution.
It's so much easier to work foam, requiring much fewer and cheaper tools. Foam is less expensive and far lighter too.
Perhaps more important still it would lead to a much freer way to experiment.
 
foam enclosures

great, so we join the rest of the world in building things that do not last and are disposable.
I'm not trying to sound like an ***, but , we have speakers that sound great and are a half a century old, because of wooden cabinets, where will these be after ten years in normal use?
I am not saying it's a bad idea, I'm just saying , great things should last and be passed down to other generations, rather than end up having to be thrown out because the enclosure slipped out of your hand.
Why not line your cabinets with it?
If this site an others are about quality of sound, so should they be about quality of construction and beauty for future generations to enjoy.
 
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There are advantages to wood in terms of durability. But try moving a Baltic birch 30in wide synergy horn around made of BB vs foam core. I think the ability for people living in small spaces with no wood shop or power tools is a huge factor. That was certainly where I came from. It just turns out that it sounds quite good if not great. I have had a couple fall and break or dent a corner. But you simply slice off bent part and graft on repair part. Like new. For people who are light and mobile, reference monitors like what I made, weigh in at weight of drivers plus a little for the cabinet make a huge difference if having to lug around. I am starting to have a few wooden baffles now but that is required to suspend 40lbs of drivers. I admire people with nice wooden builds certainly. We can't all have that luxury though.
 
Since foam is much lighter it will be much less likely to break, chip or scratch when handled roughly. If not filled with brome based flame retardants, foam should last at least as long as wood. Often speakers are thrown out because of cosmetic problems not because they don't work.

Another interesting avenue would be to make speakers out of thick papier-mâché. It would take time to find the right formulation and drying time would be an issue. But the possibilities would be endless due to the plasticity of the material.
 
You do have a point, I guess I am a little touchy, because I went to get new printer cartridges yesterday, and it was cheaper to chunk the printer and buy a new one, than simply by replacement cartridges.
I guess it's where the world is now days, we have to keep throwing away things and buying new to try and keep everyone employed.
 
great, so we join the rest of the world in building things that do not last and are disposable.
I'm not trying to sound like an ***, but , we have speakers that sound great and are a half a century old, because of wooden cabinets, where will these be after ten years in normal use?
I am not saying it's a bad idea, I'm just saying , great things should last and be passed down to other generations, rather than end up having to be thrown out because the enclosure slipped out of your hand.
Why not line your cabinets with it?
If this site an others are about quality of sound, so should they be about quality of construction and beauty for future generations to enjoy.

I understand your frustration with the modern throw-away, planned obsolescence way of manufacturing. My motivation for starting this was mainly that I live in a small Japanese apartment so I do not have access to a work room, garage, powertools or other woodworking tools and working with foam opened up this hobby to me. But I wanted to make some reference level near-field monitors. I wanted to have understanding of how the shape of enclosures effects the sound, and understanding of panel resonance and reflections. So I started to explore the use of foam in a performance way.

But I also see a lot of diy now using PVC tubing for their projects, and to me MDF is not really wood (it is a manufactured material made from glues and sawdust). And in the professional studio monitor business, many of the small portable monitors are now made from injection molded aluminum (metal bodies) which makes them heavy but very durable. My Focal CMS40 monitors are like that. There already seems to be many alternatives to wood speaker enclosures already, but I totally understand if someone else wants to make their speakers out of beautiful looking wood.

And for what it is worth, foam is non biodegradable so these foam speakers might actually last a really long time and not change appearance. EVA foam is also a soft foam, so it bends and bounces back. I can literally throw my EVA boxes and panels around (before the drivers are in) and not worry about them being damaged.
 
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