A Study of DMLs as a Full Range Speaker

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#261
bentoronto said:
Yes of course. Thank you.

But it would be a nice gesture for someone to take a minute to summarize this in two sentences for all of us who have spent lifetimes thinking resonances are great in violins but undesirable in speaker reproduction.

B.
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This is a DIY forum... if you're interested, pursue it. If you're not, then drop it. No one will spoon feed you.

Most importantly though, don't voice opinion from a position of ignorance.
 
#262
just my 2 cents , from an old rubanoide motor. there is a high shelf from 10Khz around + 8 db. and a notch at 1khz , it is playing lower then it should so it sometimes is a bit restrained

https://www.youtube.com/watch?v=4n66cmpx05I&feature=youtu.be


its driven actually by the midle part of a rubanoide coil, so it acts as a tweeter and excited the 2 boards with it at the same time

by moving the clamps and the 2 termination bars on the side you can tune the membrane to fill in gaps and get rid of peaks. but did not have time to play with it much 🙂 more a proof of concept. you could use weaker magnets and and make it 1.5 meter long, as well as decrease gapwidth when i would be able to make some sort of straight spider for the coil. 🙂
 
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#263
majerjack said:
After having my interest in DMLs rekindled on another thread, I began to wonder if we know much about the frequency response of these panels at the extreme ends of the spectrum, which I define as below 100 Hz and above 10,000 Hz. Some have noted that larger panels give better bass response, but I have not encountered any generalizations in regard to high frequencies. Can anyone point me to references which show the measurements of DML panels?
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From my experience it works following: heavy panel, thick panel, flabby panel, heavy motor, motor with large contact to panel won't do highs.

On the other side: small panel, resonant panel will sound awful, any cheap PC speaker could do a better job.

There is also a question of adaptation to air impedance, a small surface cannot have a low acoustic impedance, thus efficiency stay low. (=zero bass). As the surface of radiation increase, say above 1 or 2 m², you get full benefits of DML, more modes, more bass, less directivity, better efficiency.

I am now around the 5m² range, waiting to find bigger panels up to 8m², the maximum surface allowed by my listening room. When the radiation surface comes close to the section surface of the room, the room begin to work as a wave guide, less reflexions, less distance attenuation, huge sound.

majerjack said:
If I were to build a DML panel I would need to use it against a wall due to space restrictions. Should some kind of acoustic damping material be placed behind the speaker to limit that back-panel energy? And, is it best to terminate the edges of a DML in a stiff frame to limit the motion of those edges as well as provide mounting for the panel?
Thanks to all who can help me with these questions.
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you can put a panel quite close to the back wall if you pay attention not to do it parallel to the wall. And NOTHING should touch the panel (wires, frame, damping material)
It"s far better to make inequally rounded corners of your panels or make them "random" (sawtooth) in order to reduce standing wave inside the panel.

I would avoid the stiff frame who needs lots of care to avoid any parasitic vibration, no frame=no problem.
My panels are suspended from ceiling with small gauge nylon ropes, (yes, I'm single, in a wood cabin, in the wild)

Last important thing, you can put the motor(s) anywhere on the panel, you'll always get some nice sound, but don't name it "Distributed Mode Loudspeaker". I mean central placement and equidistance, as many have done, have few to do with DML. DML is a very special kind of beast.
20160401_150946.jpg
regards
POL
 
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#268
bentoronto said:
With all your R&D efforts, you surely have spent $50 to buy a mic to run REW (free software, Mac and Windows) freq response curves.... so that you can post them for us, 1/12 smoothing and with harmonic distortion shown.
Thanks.
Ben
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Yes, I did, with a nice set of micro+preamp+USB & HolmImpulse &SynRTA, but I've left all that stuff in my archives in Reunion Island, I'm now located in Madagascar, and I only moved with a bunch of Dayton Audio exciters, who were unavailable in this side of the world. So, no recent measurements. You'll have to try by yourself.

POL
 
#271
pol_bct said:
I forgot to mention that my forelast loudspeakers were ESL 63, and the ones before were Tannoy Dual Concentrics 15"... I won't go back to boxes, even if I get paid for. Maybe dipole OB bass.

POL
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These DML's when away from walls act much like omni directional speakers. Since there are multiple modes radiating it doesn't cancel out like dipole at 90deg to the side. A wonderful enveloping sound experience.
 
#274
Here's some food for thought. Let's look outside of the box.. 😉

Every design I read in this thread is using a conventional voice coil/pole piece with a spider to control the voice coil. I have another idea..

Let's look at things in a different light. What if the "pole piece" was part of the exciter and the voice coil excited the pole piece. No spider but using the material the sound is radiated from as the control of the pole piece..

Perhaps using a voice coil that is mounted solid and exciting a cylinder shaped magnet (Pole Piece) that is connected to the radiator. The pole piece could be something like this or smaller if the weight becomes a factor. Find a magnet to fit any voice coil that one may have on hand..

MAGNET4LESS-APPLIED MAGNETS-Neodymium Magnets-Rare Earth Magnets-Ceramic Magnets-Industrial Magnets-Magnets Wholesale To The Public

The pole piece (Magnet) can be mounted to the exciter material in a solid manner. No need to worry about a spider to keep the voice coil aligned. Being the "pole piece" is solid to the radiating material, no worries of any losses because of glue or whatever means used previously to connect the voice coil to the radiator. The voice coil is mounted solid and does not move. Some "pole" alignment is needed but can be done easily, being there is no magnetic material to fight with. Much simpler design too!
*Patent Pending*.. 🙂

Comments? Slaps? Claps? Just an idea that came to me..
 
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#275
OffGridKindaGuy said:
Here's some food for thought. Let's look outside of the box.. 😉

Every design I read in this thread is using a conventional voice coil/pole piece with a spider to control the voice coil. I have another idea..

Let's look at things in a different light. What if the "pole piece" was part of the exciter and the voice coil excited the pole piece. No spider but using the material the sound is radiated from as the control of the pole piece..

Perhaps using a voice coil that is mounted solid and exciting a cylinder shaped magnet (Pole Piece) that is connected to the radiator. The pole piece could be something like this or smaller if the weight becomes a factor. Find a magnet to fit any voice coil that one may have on hand..

MAGNET4LESS-APPLIED MAGNETS-Neodymium Magnets-Rare Earth Magnets-Ceramic Magnets-Industrial Magnets-Magnets Wholesale To The Public

The pole piece (Magnet) can be mounted to the exciter material in a solid manner. No need to worry about a spider to keep the voice coil aligned. Being the "pole piece" is solid to the radiating material, no worries of any losses because of glue or whatever means used previously to connect the voice coil to the radiator. The voice coil is mounted solid and does not move. Some "pole" alignment is needed but can be done easily, being there is no magnetic material to fight with. Much simpler design too!
*Patent Pending*.. 🙂

Comments? Slaps? Claps? Just an idea that came to me..
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You mean sort of like the RBM drivers?

Tang Band W6-2100 6-1/2" RBM Flat Panel Subwoofer 4 Ohm

Go for it, aint nothing to it but to do it , if it works it works if not oh well.
 
#278
Do these work well applied to a wall, like the drywall of the inside of a home? Because that would be awesome, but im assuming it doesnt work well because everybody would be doing it.

If I were to use foam core board, then to stand the speaker I would mount the back of the exciter to a stand, or would I want to sorta frame the foam core board to a stand? Which sounds best?

Ive bought two pairs and one paair is destined to be used with the glass panel of a shower. The other pair Id like to try as stereo speakers. And at the least if they can be conveniently located to walls then Id like to use them for home theater. Would a picture frame be a good way to get these wall mounted and sounding alright?
 
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