A Study of DMLs as a Full Range Speaker

Try double sided carpet tape.
The common ceiling tile here are with a fine stipple finish and about 1/2 in thick, seem to be made from compressd fibres a bit like a very coarse and light mdf, but are also very easily damaged and I would expect them to disintegrate quite quickly.
I do have a couple of piece of high density fibreboard about 7'x2'x1/4" I'm thinking of trying. I guess it would take three or four exciters to move them enough?
 
Here is a tip. When using EQ there is a spike (in most exciters) in the 1-2khz as well as the 4-6khz range. Lowering these spikes in the high frequency range will bring out more bass in the panel and also lessen listening fatigue over prolong periods of time.

There is a limit to EQ though as it wont make a bad (design) sounding panel sound good. Ones panels need to sound pretty good to begin with as the EQ is only to fine tune the panels.
 
Try double sided carpet tape.
The common ceiling tile here are with a fine stipple finish and about 1/2 in thick, seem to be made from compressd fibres a bit like a very coarse and light mdf, but are also very easily damaged and I would expect them to disintegrate quite quickly.
I do have a couple of piece of high density fibreboard about 7'x2'x1/4" I'm thinking of trying. I guess it would take three or four exciters to move them enough?

Nope.... Just the one.
 
These are working well for me.

I gather there is a lot of (audio) science working here that I don't fully understand as yet, and probably never will. I have tried to follow the Golden Ratio with the design, but I am not sure if it adds anything or not as these are the only DML's I've heard. You can change the frequency responce by adding blobs of bluetack around the diaphram and I am still experimenting with this, and other things.

At the moment they are in the guest bedroom to give some space between the speakers and rear wall. In my usual listening room, due to WAF, they had to be placed too close to the rear wall to work their 'magic'. I am not sure if the bed between them is adding or subtracting anything from their performance. I gather it is damping the sound though. Will try in another location soon.

How do they sound? I think their characteristics are summed up, better or as well as I could, in these two reviews, which might already be referenced here.

6moons audio reviews: Podium Sound Model 0.5

6moons audio reviews: Podium Sound Model 1
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These look beautiful!
I stumbled across 4mm Twin Wall Polycarbonate glazing panels. I believe the same material is sold for greenhouses. Not sure if it's the best material, but it looked interesting. Seems to work. ........

Interesting choice as these panels are lighter then solid polycarbonate. But don't these panels flex a lot in in 1 direction? Vertically the way you used them.
And are the small tunnels not creating resonances/distortion? Or did you close them?

Panels need to be lightweight and stiff.
Inspired by surfboards and modern boats, I suspect that polystyreen sheets with super thin (model airplane) fibreglass cloth and epoxy will be great.

Other idea is polystyreen, (wrapping) paper and sprayglue.
And maybe you wife can decide on what kind of wrapping paper...... and maybe on some finish to match the living room.

//edit: Maybe it is an idea to print pictures or artwork on the paper, although that paper will be a bit heavier.
 
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Hello Think,

Thanks for your kind words. (I can never work out how to use quotes)

Weighing some polycarbonate scrap material I have left over I estimate that the panels each weigh around 360g. It is very stiff in the vertical, and is quite hard to bend, let alone snap without scoring the face. It is certainly more flexible in the horizontal, but does not sag under its own weight if you hold it out flat.

I haven't closed/filled the tunnels, and have always thought, rightly or wrongly, that DML panels would be better if created from one solid lightweight material without laminating or internal hollows. I haven't done enough experimenting as yet to confirm any of this. The only other material I have 'played' with is 1.5mm bamboo laserply. It worked quite well in some small prototypes I made, but seemed too flexible in the panel size used here. Maybe lightweight poplar-ply might work well? I truly stumbled on this glazing polycarbonate while looking at other possible materials in a hardware store.

I would like to try carbon fibre, but unless you purchase direct from China it appears to be cost prohibitive. China also offers honeycomb carbon fibre board and polysyrene laminated board. Maybe in the future. I believe BurntCoil did some experiments with a small piece of Carbon Fibre sheet and was impressed with the sound. I would also like to try laminated polystyrene art board. The only thing I have found so far is that I believe the better the connection of exciter to diaphram, the better the result/sound. This means the few exciters I have to play with at the moment are all two part epoxied to their diaphrams, making them single use.

One thing I've read quite often, in articles discussing DML's, is that others who have tried multiple diaphram materials say that there is not much difference between the sound of 'suitable' diaphram materials.

My wife wasn't too concerned with the look of the panels, she's just not that happy with how far I want them off the back wall. Still experimenting with best placement for these particular panels.
 
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Hey GapMedia, those are just stunning in looks! Theres just something about a clear panel design that screams beautiful. Great Job!


Can you tell us a bit more about how you constructed them? Are the front and back frame routed out from a single sheet? What material did you use. Can you explain more about how easy the panel media would be to replace...the method you used to join the front and back frames, etc...


And finally, in the "how does it sound dept.", what are the lows and highs like? Are they rolled off and need EQ or are they fairly extended? Maybe I missed it but what is the panel size itself? Are the corners rounded or are they left square and the frame itself is rounded for looks. I assume you are just using some type of foam/weather-seal material and basically squeeze the panel between the front and back frame?


Geo
 
Hey Veleric,
I found out that the ceiling tiles I am using are called ‘Armstrong Recyclable Dune Supreme’

Had a good listen last night with a parts of a CD called ‘They’ll have to kill us first’.

I am finding it increasingly baffling how these DML’s can sound so good, and how the sound is emitted around and into the room. I have mine hanging by cords running through holes in each corner of the same side of a tile and then hanging from a cable stretched across my shed about two feet from the wall. Lashed together you might say.
Try walking up to the tiles and between them and then around the back and see how the sound continues to fill the air around you. It is a remarkable effect, completely unlike conventional speakers.
They are very good at revealing special clues in recordings, ambient effects and acoustic spaces seem to be better resolved or emphasised. I have have found a similar effect with BMR’s! Is this due to the flatness of the emitting surface or something else.
Puts a big smile on my face.
 
From what I have read there are a number of reasons DML’s sound so good.

Removal of the need to split the bandwidth between different drivers. Multiple drivers and the use of crossovers introduce, at the very least, phase distortions.
The increasing directivity with frequency of conventional drivers means that reflected sound in a room has a different spectrum from the original signal. Even with a physically perfect cone or dome this effect still occurs. DML’s don’t beam so they don’t have this problem, in fact they interact very little with the room.
Even though they are panels, they are not dipoles and don’t experience the ‘hot spot’ problem you get with dipoles ( I am referencing electrostatics here).
Because there is no beaming the sound remains very consistent wherever you are in the room.
There are no ‘box’ colourations.
And the exciters are very benign loads, very easy for amplifiers to drive.

Thats an awful lot of advantages over conventional speakers.
 
Hey Veleric,
I found out that the ceiling tiles I am using are called ‘Armstrong Recyclable Dune Supreme’

Had a good listen last night with a parts of a CD called ‘They’ll have to kill us first’.

I am finding it increasingly baffling how these DML’s can sound so good, and how the sound is emitted around and into the room.

jerryo,
That's great info. You might find it interesting (and ironic) that back in the early 2000's Armstrong licensed NXT technology and produced a line of DML ceiling speakers:

http://sweets.construction.com/swts_content_files/3824/E775499.pdf

But they did NOT use ceiling tiles (like Dune Supreme) for the panels. Rather, they used composite panels (phenolic impregnated honeycomb core with aramid skins), and covered them with a fiberglass scrim painted to LOOK like a ceiling tile. I'll have to try some Dune myself!
Eric
 
Firstly, these speakers are 'truly' omnidirectional, as jerryo mentions. As a lot of you seem to hang the panels from the roof it is probably not as easy to play with their positioning as with the panels I have built. I can toe them in to or out of the listening position, face them forward or towards the side walls, or even position them 90 to 180 degrees to each other and they maintain a stereo image. Basically, I can wire them in phase or out of phase and they still work. The measurements I have made of a stereo pair in REW show that no matter what I do with them positionally, within reason, the response doesn't change much more than 5dB across the spectrum from 300hz and up. It really doesn't change a lot under 300Hz either. I can see/hear why they would work mounted in ceilings just as well as on the floor. They could even be mounted in/lying on the floor facing up successfully I imagine.

geosand, yes the front and middle panels are routed out to allow for the diaphragm, double sided foam tape and weather shield. This gives the 14.5mm clearance required between exciter mounting ring and diaphragm. The three MDF panels are then screwed together. Each panel is cut from a quarter sheet of MDF and sized using the Golden Ratio to best fit. As I mentioned earlier, the exciters are epoxied to the panels. This allows for the panels to be easily disassembled, but the exciter must come off with the diaphragm. The exciter itself is recessed into the cross brace and mounted via a screw into its back, so can be released from the frame before disassembly.

The corners of the diaphragm are rounded like the panels themselves, but I am not sure if this has any affect on the sound as it is the only way I have tried it.

How do they sound? Different, right, incredibly detailed, revealing of the recording environment, and probably 'flawed' compared to what we are used to. Treble is there when it's in the recording and not when it's not. Bass is not room shaking, but you can feel it sometimes and it is always tight and punchy and well positioned in space. 'Good' live recordings sound phenomenal. It is that classic case of, "I'm hearing things in recordings that I've never heard before". I have never heard a commercial DML so have nothing to compare them with, but what is written in the 6 Moons review of the Podium 0.5 model pretty much says it all. Tonally I find some vocals sound different to 'normal' speakers, but I don't know if that is my diaphragm material or not as I have nothing to compare with. I have recordings my daughter has made of herself (RODE Mic - no compression) singing in the house, and these sound natural/spot on. Some vocals just sound like they are 'recessed', recorded in a 'tubular' space. I have a small set of DMLs I build a couple of years ago using Bamboo ply for diaphragms which I must listen to again to see what vocals sound like with them. One thing I will say is that (other) instruments, especially acoustic, sound so right that maybe what I am hearing with vocals is in the actual recording process, or electronic processing (compression?) and not a flaw within the speakers? I will do some more measuring and put the results up soon. I will also play with some EQing with REW and JRiver to see what that brings.

For the first time in a week or so I was listening to my MarkAudio Alpair 6P based pencils, and they are still enjoyable speakers to listen to, but they seem to lack the magic and a certain reality to the sound that exists with the DML's.
 
jerryo,
......
But they did NOT use ceiling tiles (like Dune Supreme) for the panels. Rather, they used composite panels (phenolic impregnated honeycomb core with aramid skins), and covered them with a fiberglass scrim painted to LOOK like a ceiling tile. I'll have to try some Dune myself!
Eric
It is not clear to me if you mean a fiberglass cloth used as a cover or is the fiberglass also impregnated with the phenolic or other resin?

Aramid is kevlar and the difference between aramid and fiberglass cloth, impregnated with epoxy, polyesther or vinylesther resin, is 3 times higher tensile strength but similar compression strength.


Found this video from DML builder with tonewood/resonance spruce. They bend the panels and use ribs on the backside making them very stiff. YouTube

Other video where someone is playing with an exciter and the big carton board which sounds best has pretty stiff edges. YouTube

Anyone already made a flexible panel with stiff edges?
A picture/photo frame might be a simple, cheap and good looking solution.

Other idea I have is a floor standing frame made of pvc pipe.

I ordered 2x 44mm exciters (€20) on Aliexpress and will go with polystyreen (white bubble stuff) sheets 80,9x50cmx3cm with paper spray glued to the front and back as a first test.
My idea is that the polystyreen is very light and flexes and (I think) thus has good damping. The paper is also light and has high tensile strength to make the panels stiff to reduce ringing/flex.
 
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It is not clear to me if you mean a fiberglass cloth used as a cover or is the fiberglass also impregnated with the phenolic or other resin?

The fiberglass cloth is used as a cover only, and not even attached to the panel itself, nor impregnated with resin. It is simply painted to make it match the color and texture of a ceiling tile with which it is intended to coordinate with visually.
 
Found this video from DML builder with tonewood/resonance spruce. They bend the panels and use ribs on the backside making them very stiff. YouTube


I ordered 2x 44mm exciters (€20) on Aliexpress and will go with polystyreen (white bubble stuff) sheets 80,9x50cmx3cm with paper spray glued to the front and back as a first test.
My idea is that the polystyreen is very light and flexes and (I think) thus has good damping. The paper is also light and has high tensile strength to make the panels stiff to reduce ringing/flex.

While I suspect that the JMC Lutherie stuff includes a lot of marketing hype, I do think the wood panels are well worth investigating.

In the past few weeks I have tried a bunch of panel materials, including polystyrene foam, foamcore, gatorply, ceiling tiles, plywood, and several other composite structures. So far, my favorite among these is a particular plywood. This plywood is about 0.2 inch thick, known as "Sureply" sold very inexpensively for use as flooring underlayment.

Generally, the other panel materials provide sound that seems to be coming from far away, down a deep tunnel. In contrast, the wood provides a clear sound, much more "in your face" and is particularly good with vocals and stringed instruments.

One downside of the plywood is that it's not as efficient (i.e loud) as some of the lighter PS foam or PS foam core composites, but I find the sound of the plywood to be much better.

I'm inclined to try adding carbon or aramid skins over a wood core, in hopes of retaining the sound of the wood while increasing the efficiency. I'm also interesting in trying other plywoods and tonewoods to see if they are any better than my Sureply.

I'm curious how many others prefer wood or wood composites for DML panels, and what specific woods they have had success with.

Here's another image from JCM Lutherie showing some details of the ribs etc on the backside of their wood DML panels.

Guitar maker Quentin Durey makes soundboard pictured Editorial Stock Photo - Stock Image | Shutterstock

Eric