Foam panel speakers

[Nat]

For those who want to experiment further, there were a couple of companies (I think Meitner was one of them) who worked on flexible panels using something similar to exciters. My memory is that at least one of them used mylar or polyethelene or something similar, damped with a layer of foam. Their explanation of how they worked was that rather than being a rigid piston, they allowed the wave to propagate outward, with the air being excited as it went, with delay as it went out acting as if the wave in the air had come from behind, from a spherical source. This explanation has some similarities to how Ohm explained their driver, and how Quad explained the concentric segments of the ESL 63, though obviously it was different. I think patent troubles boliixed up going into production, but Speaker Builder had an article on making a version yourself (the author was at pains to point out that if you tried to do it commercially, you'd probably get sued). I made a small demonstration one, and a bigger trial one. The small one was rather nice, but I never got the tension right on the big one. Interesting experience, though.

 

[John James]

I wonder what effect a circular board would have? Anyone care to experiment?

 

[MisterDK]

I wonder what effect a circular board would have? Anyone care to experiment?

I suspect - that without the corners to vibrate, you’ll probably get less bass - unless the panel is significantly larger. I was thinking about making some using round panels just for mid and highs, then below it, a separate, larger rectangular panel - in hopes of getting lower mids and bass. Still, using a single exciter per panel (they’re plenty loud).
Would be interesting to try with round panels; why not give it a shot? The exciters and suitable panels are inexpensive enough to experiment with. I just wish I could find 4x8’ sheets locally.
BTW- though I have not heard the other available exciters, I do recommend the Dayton “Thruster”. They play loudly on the small 2’ square panels, and seem to take some power when cranked up louder - and I’m running a pretty powerful amp into them.

 

[Nat]

A round panel will have one frequency at which the front and back waves start to cancel each other, since the path length will be the same all around. With a rectangle or square, you have a range of path lengths. If you want a round panel, putting the driver off center might be helpful.

 

[MisterDK]

A round panel will have one frequency at which the front and back waves start to cancel each other, since the path length will be the same all around. With a rectangle or square, you have a range of path lengths. If you want a round panel, putting the driver off center might be helpful.

The driver normally mounts off center anyway; usually a 2/5 and 3/5 location. I actually got a look at a genuine NXT (Teac) speaker yesterday and was surprised by the exciter location. It looked further into a corner than the accepted 2/5-3/5. That speaker was at a thrift store; I should go back and buy it just for measurements (probably just a buck or so).

 

[Nat]

I didn't know there were accepted norms in foam panel speakers.

No corners in a circular panel, of course...

 

[MisterDK]

I didn't know there were accepted norms in foam panel speakers.

No corners in a circular panel, of course...

People have been building ‘em for a while. Check out some of the threads on audiocircle, partsexpress and diyaudio.
These speakers have some things I like about them - inexpensive, omnidirectional, great clarity, and some things I don’t - little bass and lack of a good soundstage. Hoping my next (larger panels) set will sound better. I expected to have little bass and need for a sub woofer, but I’d like a bit more bass out of the panels too..

 

[Nat]

I built mine back a decade or more ago, so I've been aware of them a long time. I just didn't realize there was a 'normal' in what is basically a DIY kind of thing, shipping such speakers being not exactly an attractive option for manufacturers.

 

[DMLBES]

I didn't know there were accepted norms in foam panel speakers.

No corners in a circular panel, of course...

The accepted norms are based on ones design. For my design my exciter placement is smack dab in the middle of the panel.

Even in a rectangle shaped panel the corners are rounded basically making it a elongated octagon.

If you look at this video it will give you a idea why the corners should be rounded. If you look at the corners the salt never goes to the very tip of the corner instead it prefers to cut the tips off.

 

[John James]

^ ^ ^

Thanks for the video!

I would like to see that done with a circular plate.

 

[Poultrygeist]

Here's another interesting project using foam boards - The Cornu Spiral Horns

https://www.diyaudio.com/forums/full-range/225622-building-cornu-spiral-horn.html

 

[Markoneswift]

I finally got my Dayton Audio exciters yesterday - took a while from the States to NZ! I've been following the DML / foam panel concept for quite a while - pretty much since watching the stuff on Youtube by Tech Ingredients.

I ripped the fronts off two pizza boxes late last night, then attached the Daytons to the box fronts with adhesive tape (mine do not have self adhesive pads on them). I ran my amp speaker outs through a small Mordaunt Short sub and then on to the pizza speakers. Wowzers - sounds great! Even with the cardboard panels resting on top of my hifi unit, rather than suspended, they sound great with really impressive mid and high range. The sub really helped things along and Fast Car by Tracy Chapman really sounded great.

My local DIY supplies place has the XPS panels at very reasonalbe prices so I'm going to step up to a pair of those and look at suspending them from the ceiling for a more extended trial run. Good times

 

[Markoneswift]

Has anyone tried monuting exciters on 12" LP records at all? Just wondering what they would sound like -= probably bad, due to commets about circular panels above, I guess?

 

[MisterDK]

Has anyone tried monuting exciters on 12" LP records at all? Just wondering what they would sound like -= probably bad, due to commets about circular panels above, I guess?

I think they may be too small to sound good, but they may make decent upper-midrange. If material selection and shape is optimized, I think that bigger is better (despite whatever I may tell my wife..). ^_^

I’ve been enjoying my 2x2’ XPS panels for a few weeks now and think they sound better all the time - but still don’t deliver the bass. I’m using them with an old AR powered sub, and that certainly helps. When I find the time and the XPS I want in 4x8’ sheets (seems no seller near me stocks it), I’ll make another pair in 3x5’ - and then start on my big transmission line, El Pipe-O type subwoofers.

 

[Markoneswift]

I think they may be too small to sound good, but they may make decent upper-midrange. If material selection and shape is optimized, I think that bigger is better (despite whatever I may tell my wife..). ^_^

I’ve been enjoying my 2x2’ XPS panels for a few weeks now and think they sound better all the time - but still don’t deliver the bass. I’m using them with an old AR powered sub, and that certainly helps. When I find the time and the XPS I want in 4x8’ sheets (seems no seller near me stocks it), I’ll make another pair in 3x5’ - and then start on my big transmission line, El Pipe-O type subwoofers.

Sounds like a plan! I was looking around in the recycling shop at the city dump last week and noticed a whole stack of boxes filled with acoustic ceiling tiles. If you've seen the Tech Ingredients videos, he seems to speak quite highly of the acoustic ceiling panel as a maetrial so I might grab a box - they're only $20 for a whole box of the things.

 

[Markoneswift]

I've just moved my trial onto some different panels. They are sign boards made from a type of corrugated plastic.

They sound great - I ran some Sade through them and I'm really impressed !

 

[Markoneswift]

This is the material.....

 

[rothwellaudio]

Has anyone tried monuting exciters on 12" LP records at all? Just wondering what they would sound like -= probably bad, due to commets about circular panels above, I guess?

I was looking around in the recycling shop at the city dump last week and noticed a whole stack of boxes filled with acoustic ceiling tiles. If you've seen the Tech Ingredients videos, he seems to speak quite highly of the acoustic ceiling panel as a maetrial so I might grab a box - they're only $20 for a whole box of the things.

I've just moved my trial onto some different panels. They are sign boards made from a type of corrugated plastic.

The material should be light and stiff. 12" LP records are not at all light. That corrugated plastic looks ideal.

 

[RickeyM]

The accepted norms are based on ones design. For my design my exciter placement is smack dab in the middle of the panel.

Even in a rectangle shaped panel the corners are rounded basically making it a elongated octagon.

If you look at this video it will give you a idea why the corners should be rounded. If you look at the corners the salt never goes to the very tip of the corner instead it prefers to cut the tips off.

Very interesting video. I too would like to see that with a circular plate as well as some other shapes. I'll have to study it.

Interesting stuff these flat panel speakers. Seems like a good fit in places that don't lend themselves to conventional speakers, kitchen/bathroom/workshop. Instead of in-wall speakers, on-wall speakers or paintings as speakers.

 

[rothwellaudio]

Round panels with the exciter in the middle are the worst design because you get a dominant resonance. These speakers are called DMLs, Distributed Mode Loudspeakers, but the modes aren't distributed evenly with a round panel and the exciter in the middle.