Motor-based planar speakers-can it be done? - diyAudio
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Old 3rd June 2006, 05:05 AM   #1
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Default Motor-based planar speakers-can it be done?

I've been looking through speakers, and it appears that some rather decent speakers (which more-or-less fit the definition of "planars") use a combination of a standard electromagnetic motor and another non-electrically active material to actually make the sound. Examples include the Soundpads and "Personal Planars".

Soundpads:
http://www.thinkgeek.com/electronics/audio/6bd8/

Odd wire-magnet-and-diaphragm design I don't quite understand:
My DIY planar speaker!

"Personal Planars"
http://www.decware.com/panels.htm


I personally like the idea of using a standard electromagnet assembly to drive a flat panel; that way, one can use a standard amplifier without transformers or high voltage, while keeping a large degree of the excellent sound associated with planars.

Also, I was thinking about using a method of driving these speakers used in "featherweight" R/C airplanes: Rotational actuators.

You can see one here:
http://www.ekmpowershop2.com/ekmps/s...T&productid=77

By placing a magnet in the center of a coil, you can make it spin in alternating directions by putting A/C current through the coil. Once the vibrations are produced, you then just apply 'em to the speaker membrane. However, due to inertia, I doubt these would work well at high frequencies.

Alternately, one could put a coil on the membrane and have it around a centrally placed magnet, somewhat like conventional speakers.

Finally, one could also try a piston-style design, with a small magnet with a coil on each side, running push-pull. You then thread a pushrod out to the membrane; using a high-strength magnet, you'd likely get decent efficiency, too.

So, any tips for doing this?
Or am I out of my gourd?
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Old 3rd June 2006, 06:00 AM   #2
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It must be something in the Bratwurst.
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Old 3rd June 2006, 06:12 AM   #3
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Seriously:

http://www.magnepan.com/maggie_tech.php
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Old 4th June 2006, 01:00 AM   #4
thadman is offline thadman  United States
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by using a voicecoil you raise the moving mass of the driver greatly, which defeats the main purpose of the planar/ribbon design (excellent transient response).
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Old 4th June 2006, 01:30 AM   #5
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I have no personal experience with much of what you posted other than the "soundpads", and I don't recommend them for anything other than pure novelty.

"Distributed Mode Loudspeaker" is the technical term for them, developed by a company called NXT. Its takes a lot of research, development, and access to the right materials to even come close to making a "DML" worthy of listening to. Even "DML" products made by big companies fall extremely short of anything close to HiFi.

I have spent many hours and quite a few dollars messing with this technology, and I don't consider any of it well spent.
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Old 4th June 2006, 03:37 PM   #6
el`Ol is offline el`Ol  Germany
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Maybe you don`t know these:
http://www.sibatech.co.jp/FAL/FAL%20index.htm
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Old 4th June 2006, 04:38 PM   #7
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I guess you've got a point.

One idea (shown in the second link) is to put an extrelely long, thin coil of ordinary copper magnet wire along the length of a mylar ribbon. Although not as thin or as light as a real ribbon driver, you would'nt need transformers to drive it, and it could be made relatively cheaply if a source for neodiyum magnets could be found. Efficiency likely would'nt be too bad, either.


EDIT:
Now with picture! Can you tell I made it in MS-paint?
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Old 5th June 2006, 08:37 PM   #8
el`Ol is offline el`Ol  Germany
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Search for neodymium at Ebay yields 632 hits.
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Old 6th June 2006, 10:22 PM   #9
Ron E is offline Ron E  United States
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Museatex did the voice coil on planar diaphragm thing many years ago.
I know they cost a lot for what they were and they never went over well. Supposedly they sounded good when dialed in, but I don't believe what I don't hear. 90%+ of high end audio is just a con game.

Manger is essentially what you describe, but with damping elements and variable stiffness. I haven't seen a DIY Manger, why not try your own?
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Old 6th June 2006, 11:06 PM   #10
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Hmm...interesting.

I was wondering about the viability of speakers using a standard coil mounted in the center of a taut-streched piece of plastic. (This would be a lot like an electrostatic speaker.) Using a magnet on each side of the coil, you could drive it in both directions equally. As an added bonus, the field remains somewhat linear througout; as the coil moves farther from one, it moves closer to the other.

Also, could someone explain how the "personal planars" speakers work? I can't figure it out.

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