A Study of DMLs as a Full Range Speaker

Good-luck-mate.
Hi and welcome.
Your first question about gluing paper to dmls.
This depends on the material,eps for instance will be affected more than say a heavy material.
Just lightly touching the edges of an eps panel will alter the sound.
Lightly touching a heavy ply panel will make no difference at all.
Paper would heavily damp eps.

Question two about the ply panel showing through the canvas.
I would think it very hard to glue a panel to the back of canvas and not make it show.
Ply tends to bow a little,plus the gluing ,also you only need to be a fraction out with the mounting and it will disturb the canvas,so if perfection is what you are after then probably not a good idea.

Question three .
Yes I have mad a Ali panel in the past.
But I used two 1/4mm thick sheets and glued them together with spray mount.
This damped the panel well but my exciters were only 10watts ,so the exciters got a little too hot if played at anything above average listening levels
Back then 10watts was about the most powerful reasonably priced exciter going.
Now you have 40 watt exciters and more,which would probably have driven to them ok.
I looked at the exciter you want to order and it is a 40watt exciter,so should drive most materials,but it did say back ordered !
Personally I'd take the easy option first ,and glue the exciter to the Ali panel with the frame attached just to see how it sounds.
No damage would be done to the important front side and if it sounded promising you could take the next step of damping or, and maybe removing the frame.
The frame might actually help damp the panel ringing and flapping?
If rigid enough ?
Don't forget that moving the panel close to a wall will reduce the low end considerably,making it sound a bit tinny with out a sub.
But I recommend listening first before you start pulling things apart.
I did use a 5mm thick sheet of eps glued to the back of one of my single sheet test panels ,but found it was a bit overkill !
I think I still have it lying around here somewhere.
Paper and spray mount or some other light of heavy glue on the back side might do a better job ,and also keep your front side free.
A picture of the type of frame you have and how it is mounted would be helpful to see if it could work ok.
Or could be adjusted to another type of mount with foam?
Hope this is of some help?
Steve.
 
I have experimented with different exciter one on the pink insulation board that is commonly used in the you tube designs from Tech ingredients - and also on thin finish ply from home depot. I must say the thin ply sounds much better but rings because the wood reverberates below say 2K but above 2K it does not. I tried 2 exciters on 4ft by 4ft panels and they did produce very good low frequency's when you listened closely but you could hear the ringing in the background clearly. Damping seems to be better in the foam but it also causes more peaky sound
 
Bob Johnson.
Hi.
A 4ft x4ft ply or any other material of that size will happily sing along to the music long after the music has stopped.
When you start getting too small the ply panel will start to sound shrill and hard sounding.
Many years ago I covered a 12inch or so ply in blu-tack to try and stop the harsh sound,without success.
what was the size and thickness of your smaller ply panel?
It's a shame tech ingredients and parts express both promote 1inch xps ,mainly I believe, because it is easy to work with ,cheap and and easy to get hold of.
You shouldn't have to use EQ to try and correct poorly performing materials.

Smaller panels using a more suitable material can out perform large panels in a domestic environment ,even in the low end,such as the art panel, for instance.
I have a 6inch test card panel for testing a dome ,that has a better performing low end down to 100 hz than my 5mm 2ft xps
You have to get the combinations right,I suspect the 5mm xps is too lossy and needs to be smaller.
I will cut the size down to see what happens to its performance as it gets smaller ,before I take it down.
Steve.
 
Hi aagas,

Thank you for your guidance.

I had not thought of making, or taking a pre-made, composite panel and then having the photographic image printed on it. I will look to see if there is a suitable printing service here in Melbourne.

I am inclined to initially shy away from trying to make my own composite panel of Aluminium flashing on EPS board (although I'm interested to know what it would sound like as a DML) because I'm not confident enough with my limited tools and modest skills to come away with a printing surface that is sufficiently devoid of visible blemishes.

I did think of buying (hopefully cut-to-size) composite sheets (e.g. Al skinned honeycomb) with the thought of applying a paper print to the front with adhesive. My preliminary look at the costs made it appear to be one of the more expensive options, but I might look again at suppliers.

Your repurposed cabinet doors seem ideal. One of the difficulties I think I would face with an ordinary cut composite panel would be making the edges look good. I imagine the cabinet doors have edges that are finished? Would love to get my hands on some.

Cheers,
Chris
 
Has anyone experimented with one panel with two drivers for Embracing Sound ™ like stereo? IE stereo difference is subtracted/enhanced by phase reversal in the other speaker.
Could make for a very compact and interesting stereo experience.
Think Geneva sound, just much better.

Mid/side stereo would probably not work, since the a DML panel sticking out at 90 degrees between two tightly spaced stereo speaker pair panels is not a true dipole.
 
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Hi Steve,

Thank you for sharing your experience.

1. What you are saying certainly makes sense to me, intuitively also. I think I will maintain this approach as a possibility in abeyance for the time being.

2. Once again what you say rings true. I may try some experiments without gluing the timber panel to the canvas, just to see what happens.

3. I ordered a couple of the exciters from a local distributor who said they were in stock (no other suitable models were).

I agree that taking a progressive approach with modifying the existing Al picture seems prudent. Photos of it unmodified are attached. The main challenge will be detaching the frame from the rear surface; I'm guessing the adhesive is some kind of double sided tape. If I can separate the two without damage then cleaning up the leftover adhesive shouldn't be a problem.

There is no real alternative, I think, to having it hanging on the wall, so whatever that entails I guess I'll just have to deal with it. I'm hoping the DSP (and sub) might help a little with that, ultimately. I think I read in the Soundwall Nova literature that they consider the back-surface sound radiation to significantly enhance the sound quality, but I'm not sure how much credence to place on that and I have no personal experience either. They also say that foam stand-offs between the picture frame and the wall helps, which does seem to make sense regardless.

Cheers,
Chris
 

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20210619_085736.jpg Spedge,
I painted the front of my 12x16" canvas panels with black thinned acrylic paint, and you cannot see any indication at all of my ply panels on them. I showed them to 3 people who saw them from afar and close up, and until I turned them over, were even unaware that they were the source of the sounds, much less having the exciters on them. I tried to rotate the pipture, but couldn't figure out how to.
I found the hard way that both sides of the canvas have to be coated with either thinned pva or thinned paint. I started listening to them with a bass-heavy song, and the canvas stretched away from the spine by about 1/2" within the first 1/2 hour. I coated the back of the canvas with colored thinned pva, and it tightened right back up. I let them dry overnight, and they worked quite well the next day. I do have a couple of buzzes at the lowest levels to work on, as I have hastily hung them with ugly temporary 1x2" hangers from my drapery rods, and they are touching the drapes. I have filled in with the sub, and it adds a lot of the bottom end. I am still in the breaking-in stage, though, so I will let them run for a week, then re-evaluate. I have a pair of about 18x15" melamine foam pad mats in the fold in the drapes behind the DMLs, and the DMLs are about 10 or so inches from the window.
 
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Chris,

You may overestimate the difficulty of fabricating aluminum composite panels from foam and flashing.
You can easily cut/work aluminum (even thick aluminum) with hand tools.
It adheres well to almost anything with contact cement.

Flashing usually has an almost pristine surface, that should make for a great photographic printing surface.
You can even polish it with fine emery paper or jeweler's rouge.

Clean the aluminum surface well with alcohol before trying to stick it to anything.

3M (click for web page) has a variety of interesting adhesives beyond contact cement.

You could put a simple thin aluminum or wood frame (the same thickness as the core) around the core and glue both to the aluminum.

You could also do a test of just laminating the aluminum to the foam; allowing the aluminum to overhang the foam, then cutting the whole thing to size with a track saw, table saw, router, or even a circular saw against a guide. It might give you an edge that worked fine.

An Alternative ...
(suggested to me decades ago by a chemical engineer who developed adhesives)...

  • Make a very light frame;
  • Affix one aluminum skin to one side with adhesive (maybe even VHB tape);
  • Rough up the inside surface of the first aluminum skin;
  • Clean the inside surface with alchol;
  • Whip up PVA or a 3M Acylic glue in a blender or with an egg beater (whip in as much air as possible);
  • Pore the whipped stuff into the frame;
  • Lay the second aluminum skin on top.
This approach enables you to make your own foam, which fills all spaces and bonds very well to everything.

It also enables you to completely control the thickness of the panel.

Also, you'll find flashing cheap and in long rolls so you'll have lots with which to experiment.

I'd likely make panels with a core of somewhere between 10mm to 20 mm.

Keep in mind that in these construction methods the foam doesn't produce the sound.
Rather, the foam separates the aluminum skins. The further apart the aluminum skins the more rigid the panel.

A well constructed aluminum composite panel of a given thickness will approximate the rigidity (tensile strength) of solid aluminum of the same thickness with far less weight.

Just an amazing engineered material and you can make it at home...
 

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Jaxboy.
Yes I was impressed with the shine on the black panel,no sign of the panel showing through.
It's probably best not to drive the panels below the lowest point the panels can output, I rolled mine off at 45hz to stop unnecessary flapping.
Depending on what is causing the buzzing,if all fails you can reduce the low frequencies until it stops and use this as your new cross over point.
This will allow you to play music a lot louder with no problems.
I had to do this with my art panel ,as I over tightened the canvas with wooden dowels to see the frequency change, wetting the panel didn't evenly tighten the panel again ,cascamite and canvas are not a good match.
Steve.
 
aaagas.
This method in your drawing might be good for strength ,but you have to be careful you are not building a 20mm wall between you and your exciter.
The primary radiating surface will be on the exciter side and even this will be heavily damped by this three layered panel.
Tech ingredients do a good job of strengthening 1inch XPS with fiberglass in their videos,but I'm not sure if this will make XPS any better suited for dml use ?
There is still the damping and insulting layer inbetween?
Steve.
 
Good-luck-mate.
I know that now days exciters come with sticky tape already attached to the exciter foot.
But you could ,if you are worried about committing to one panel,try a little bead of blu-tack around the foot for a temporary fixing.
As long as the panel is tilting forwards or facing down the exciter shouldn't fall off,it would even help if you used the lead out wires to help support the exciter weight by taping the wire to the top of the frame.
This worked for me quite well on some ply panels I wanted to give a quick test.
Steve.
 
Hi Steve,

I don't think the insulation will have a dampening affect in this kind of configuration.

My current conjecture...

The rigidity of the aluminum skins - increased by the separation of the core - ought to vibrate the front and back of the panel in unison as if the composite really does become one thing.

Empirical experiments will provide more information.

Pretty cheap and easy to try.

More to come...

Andreas
 
Spedge,
Actually, the panels are rather matte. It was just the reflection because I took the picture at an angle to show that there was no bulge from the exciters. I do believe that rolling off the frequency at about 45Hz is the solution to the buzz. However, I am not an audiophile, so I am a tyro about filters and roll-offs, etc. I went on-line and found that a 100 uf cap and a 35 ohm resistor would roll off my frequencies at 45 Hz. Is that with a 4 ohm speaker, and what sized resistor wattage minimum for moderate listening do I need? Do I even need the resistor? You have been so helpful so far, and I so much appreciate your help.
 
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I am using a computer equalizer, but in the music stream, it is pre-sub also. I can't pull the sub signal off ahead of the equalizer. My sub is powered, but it's a mono one, so I am running it through a 2.1 amp and am just keeping the sub volume from that amp low so I don't overpower the plate amp of the sub. I want the sub to play as low as it will go, but I want to keep the bottom end off the DML. That is why I need to put a high-pass on the DML. I will never get to even small-party volume level with them. Do I need a resistor with the 100uf cap, and is that the right sized cap? The plug-in calculator said a 35 ohm resistor.
 
Jaxboy.
I'm no expert on passive xo but 100uf for a 45hz xo doesn't seem right to me.
For that low a roll off I would expect something more pricy?
Probably something I wouldn't want in line with the exciter anyway.
I did have a book years ago on xo design, it's around the house somewhere, but hopefully someone more knowledgeable might chip in and save me having to turn the house upsidown.
Steve.