Soldermizer,
First, please pardon the misspelling in my previous post. I haven't looked back at Li's abstract of conclusions, but he does list the DML efficiency as 0.92% and that of his conventional loudspeaker as 1.81%. He also indicates the overall sensitivity of the DML as about 7.5dB less than the conventional speaker, so I don't think there's really a discrepancy, at least in his test results.
I do think he used a very small panel, about 17 x 20 cm, and all his trials were with one panel material and one exciter position. You may learn more practical results about this technology with your experiments than Li did.
First, please pardon the misspelling in my previous post. I haven't looked back at Li's abstract of conclusions, but he does list the DML efficiency as 0.92% and that of his conventional loudspeaker as 1.81%. He also indicates the overall sensitivity of the DML as about 7.5dB less than the conventional speaker, so I don't think there's really a discrepancy, at least in his test results.
I do think he used a very small panel, about 17 x 20 cm, and all his trials were with one panel material and one exciter position. You may learn more practical results about this technology with your experiments than Li did.
"- Exciters are slightly less efficient than conventional loudspeakers. As a very rough guideline, expect to replace one speaker with two exciters in retrofit applications."
Buyers Guide - Exciters
OK either I'm wrong or somebody else said that DML is more efficient or both!
"Practical?" Me????
Mentioned earlier in this thread and possibly of use in tuning or just making a mess! Is there any point in looking at the resonances (Chladni or drum head modes) of a panel? All we need is a sine generator, some sand or flour (send the wife away for the afternoon first!) ... and blast the membrane. Having not done this at all, I am just speculating but even if we identify the modes and nodes, does this help in placing the exciters? The mere act of adding mass or damping to the panel changes everything, doesn't? Sort of like Heisenberg's uncertainty principle applied to audio tinkering.
Buyers Guide - Exciters
OK either I'm wrong or somebody else said that DML is more efficient or both!
"Practical?" Me????
Mentioned earlier in this thread and possibly of use in tuning or just making a mess! Is there any point in looking at the resonances (Chladni or drum head modes) of a panel? All we need is a sine generator, some sand or flour (send the wife away for the afternoon first!) ... and blast the membrane. Having not done this at all, I am just speculating but even if we identify the modes and nodes, does this help in placing the exciters? The mere act of adding mass or damping to the panel changes everything, doesn't? Sort of like Heisenberg's uncertainty principle applied to audio tinkering.
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It doesn't look right on the fixing between driver and panel.
Try lengthening the timber and using soft material to couple the panel. Keep the mounting points away from one another. Like the one on the right in my sketch. The driver itself and the panel should be supported separately.
Or, if your driver can support itself, then ditch the wood blocks between frame and panel, and the timber. Then suspend the whole thing by other fixing points on the panel itself. By this, you support the panel only, and let the driver 'float' on it (by its own suspension).
And, your panels looks very near the wall and not much space around them. If they have to be that way, put some sound absorbing material between panels and wall to reduce reflections.
Try lengthening the timber and using soft material to couple the panel. Keep the mounting points away from one another. Like the one on the right in my sketch. The driver itself and the panel should be supported separately.
Or, if your driver can support itself, then ditch the wood blocks between frame and panel, and the timber. Then suspend the whole thing by other fixing points on the panel itself. By this, you support the panel only, and let the driver 'float' on it (by its own suspension).
And, your panels looks very near the wall and not much space around them. If they have to be that way, put some sound absorbing material between panels and wall to reduce reflections.
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CLS: Thank you for the suggestion. I will do the easiest first: remove hard (wooden) feet of speaker and instead find a softer means of connecting the timber at its far ends. I am leery of free-floating the panel ( = only attached at speaker cones). I had voice coil alignment issues when I tried that with the smaller coroplast panels. A conventional speaker's suspension is tuned to support a lightweight cone, not cone + 16 square feet of foam board 
I guess extra foam board qualifies as soft material for the new stand-offs.
I guess extra foam board qualifies as soft material for the new stand-offs.
CLS, thank you, I have done as you suggested (removed the wood spacers at speakers and have "soft" spacers (foam board) closer to ends of timber piece.No doubt you are correct to suggest a panel is better not against or near a wall. However, in my current room (it is small) as hung is probably the best place. Also, if the DML is bipolar or bipolar-like, the backwave should not be as destructive as a dipole?
There is much better bass. EQ is constantly being tweaked, of course. I seem to have peaks at 300-400 Hz and also around 2.5K. Right now, EQ-ed flattish but letting the highs roll off naturally. Sounds very good. With very bassy stuff (electronic, trance etc.) there are still some buzzing issues to hunt down. Other than that, I've heard no distortion even driving them quite hard. I know the science behind the DML is quite complex, but I am amazed the possibilities driver + adhesive + panel offers. Hell, I might even try a legitimate exciter someday
I'm surprised there hasn't been more experimentation with DMLs by hobbyists. It doesn't get much easier than this and no box or wood shop required.
Xrk971: you will be happy to know that I bought a few dozen sticks of hot glue at a yard sale yesterday, "just in case." You probably would have bought the entire stock
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This is just a tangent, but during my dissection of failed drivers, I have seen just how fine the wire on a voice coil is (on a Pioneer/Bose CTS type 4 1/2 driver.) It is very fine wire, what 30, 40 gauge? And people are worried about the quality of their "interconnects" ... leaving aside the high prices some people pay for their "audio jewelry", isn't the current-limiting factor in a speaker the voice coil winding? Granted, this is not a high power subwoofer but isn't theirs still thin wire? So why do purists need cables that carry enough power to light the neighborhood
Audio Myths !
Myth: Using audiophile speaker cables improves the sound, compared to an equally heavy gauge of normal electrical wire.
Dispelling Popular Audio Myths
Myth: Using audiophile speaker cables improves the sound, compared to an equally heavy gauge of normal electrical wire.
Dispelling Popular Audio Myths
It doesn't look right on the fixing between driver and panel.
Try lengthening the timber and using soft material to couple the panel. Keep the mounting points away from one another. Like the one on the right in my sketch. The driver itself and the panel should be supported separately.
Or, if your driver can support itself, then ditch the wood blocks between frame and panel, and the timber. Then suspend the whole thing by other fixing points on the panel itself. By this, you support the panel only, and let the driver 'float' on it (by its own suspension).
And, your panels looks very near the wall and not much space around them. If they have to be that way, put some sound absorbing material between panels and wall to reduce reflections.
Thanks for the explanations CLS. These are beautiful diagrams. Did you draw these? You should write a textbook on DML's.
Thanks for keeping this thread going. I have been a bit busy with other projects to do any more "studying" on DML's
It's just drawn by MS powerpoint and saved as .png file. I'm glad you find it useful.
As to the positioning of the panel in room, even though it's almost omni, you'll find the location and orientation still matter.
The panel is very light. It can be easily affected by the reflections (by the wall). It'd be better to keep the surrounding as open as possible. Or avoid parallel to the wall, and avoid trapped/restricted space formed by the panel and walls as you can. If being close to the wall is unavoidable, some damping material behind the panel can be helpful.
As to the positioning of the panel in room, even though it's almost omni, you'll find the location and orientation still matter.
The panel is very light. It can be easily affected by the reflections (by the wall). It'd be better to keep the surrounding as open as possible. Or avoid parallel to the wall, and avoid trapped/restricted space formed by the panel and walls as you can. If being close to the wall is unavoidable, some damping material behind the panel can be helpful.
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Tsk, tsk! I am lackadaisically pursuing a MA degree and still find time to tinker with audio As proof, I submit that I failed my comprehensive exams a month ago
But this DML thing is fascinating...the Transmission Line/Line Array is all but forgotten (it has been working, so moving on to damage the next item...)
As proof, I submit that I failed my comprehensive exams a month ago But this DML thing is fascinating...the Transmission Line/Line Array is all but forgotten (it has been working, so moving on to damage the next item...)
Poor xrk971...pimping this DML thing and almost no call for hot glue Overall you've given good information, but the stand-offs are best minimized as per CLS's notes above. My current "test bed" confirms this; 4 (x2 ) stand-offs = very little bass; 2x2 = better; all the wooden ones gone and two "soft" (foam core) stand-offs at end of my board = bass!
For the most part, music sounds great. My "source" is an obsolete Samsung Galaxy playing streaming music (Pandora). For whatever reason, the audio on this phone does a "pop" between songs, not objectionable but a "thump" on a normal speaker but on the 4x4' panel it is more of a "knock" almost like at a door. Guess I have to de-resonate the panel (but I thought that was the whole idea???) Confused!
Overall you've given good information, but the stand-offs are best minimized as per CLS's notes above. My current "test bed" confirms this; 4 (x2 ) stand-offs = very little bass; 2x2 = better; all the wooden ones gone and two "soft" (foam core) stand-offs at end of my board = bass! For the most part, music sounds great. My "source" is an obsolete Samsung Galaxy playing streaming music (Pandora). For whatever reason, the audio on this phone does a "pop" between songs, not objectionable but a "thump" on a normal speaker but on the 4x4' panel it is more of a "knock" almost like at a door. Guess I have to de-resonate the panel (but I thought that was the whole idea???) Confused!
Thump and knock, they are different in the harmonics, and/or in the different proportion of attack and decay of the sound.
I think bending wave (distributed mode) we need here is different from the resonances of standing waves.
Ideally, there should be many uniform excitations across the whole area. And they cease after a proper (very short) period. If there's any severe local or prolonged resonance, it's certainly a bad thing.
There're many factors: inherent resonance of the panel itself, location(s) of the exciter(s), methods/locations of the suspension (of panel), shape of the panel... etc.
I think bending wave (distributed mode) we need here is different from the resonances of standing waves.
Ideally, there should be many uniform excitations across the whole area. And they cease after a proper (very short) period. If there's any severe local or prolonged resonance, it's certainly a bad thing.
There're many factors: inherent resonance of the panel itself, location(s) of the exciter(s), methods/locations of the suspension (of panel), shape of the panel... etc.
CLS: Yes, I will work on damping resonances but first...
Last night I was listening to the "ambient piano" channel and I heard (ack!) distortion...can't be sure of course, but sounds like harmonic distortion due to voice coil being out of alignment ("likely suspect"): I will have to re-check my constantly-being-revised mounting stand-offs.
I'm surprised I don't see it more here: I read back around 1980 and believe it is true, that a recording of piano most valuable (or liable?) to reveal any faults in the playback chain, distortion in the speakers for example
Last night I was listening to the "ambient piano" channel and I heard (ack!) distortion...can't be sure of course, but sounds like harmonic distortion due to voice coil being out of alignment ("likely suspect"): I will have to re-check my constantly-being-revised mounting stand-offs.
I'm surprised I don't see it more here: I read back around 1980 and believe it is true, that a recording of piano most valuable (or liable?) to reveal any faults in the playback chain, distortion in the speakers for example
Has anyone tried a different "shape" of the excited material? Maybe triangle shape and mounting the exciters at one of the widest points? (Bottom)
The surface area would get smaller towards the top, perhaps enhancing the treble response?
I mounted some to the top portion of tall, narrow cabinet doors. Most of the treble response was towards the bottom, near the floor...?
The surface area would get smaller towards the top, perhaps enhancing the treble response?
I mounted some to the top portion of tall, narrow cabinet doors. Most of the treble response was towards the bottom, near the floor...?
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I haven't explored what the resonances are (and not even sure how to except throw sand on it). For my current pair, I chose the University guy's "golden ratio" of (about) 0.95:1 or for mine, about 45x48". Trapezoid shape guaranteed due to sloppy cutting Also I rounded the corners because that is supposed to help.
For time being I've banished the piano distortion. Trying different methods to hang the panels and (right now) one speaker is fine sitting on desk against back wall, because I keep pulling the hook out of the ceiling
Also I rounded the corners because that is supposed to help. For time being I've banished the piano distortion. Trying different methods to hang the panels and (right now) one speaker is fine sitting on desk against back wall, because I keep pulling the hook out of the ceiling
