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A Study of DML's as a Full Range Speaker
A Study of DML's as a Full Range Speaker
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Old 7th April 2015, 10:39 AM   #21
CLS is offline CLS  Taiwan
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That will be interesting to try. But I'm worrying the coupling between exciter and the bridge is difficult. It's too thin.

I've tried holding an exciter (by hand) and let it drive a foamcore board at its side. There's some sound, but horribly squeaky.
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Old 7th April 2015, 11:12 AM   #22
xrk971 is offline xrk971  United States
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A Study of DML's as a Full Range Speaker
Perhaps it may be enough to attach the excited to the central portion of the back panel of the violin or cello. Easy to try.
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Old 7th April 2015, 11:26 AM   #23
CLS is offline CLS  Taiwan
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Yes, that'd be much easier. I guess the location of sound post would be the 'sweet spot'

It's very near the HF side of the bridge, must be a good choice to excite.
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Old 7th April 2015, 05:08 PM   #24
BYRTT is offline BYRTT  Denmark
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A Study of DML's as a Full Range Speaker
Quote:
Originally Posted by CLS View Post
..........One thing I can't explain is the bipole character, polarity, and the impulse response.

If it is indeed bipole, the polarity on both sides should be the same. So, it should be no different driven by normal or inverse polarity. But how can we explain the impulse response? -- Very high positive peak and very low negative.
IR look some ala a wideband 3 or 4 way with some point FIR correction , then how does group delay and square waves reproduction look like and is it minimum or non minimum phase system .
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Old 7th April 2015, 07:40 PM   #25
Greg B is offline Greg B  United States
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It would be ideal to have some sort of laser interferometry set up to really develop this sort of driver. That should be the next thing installed in your lab xrk, and CLS too...

However, I have a low tech solution: get out the glitter and a signal generator.... It will readily detect chladni patterns.

In theory, the goal should be an expanding wave with an origin at the motor that matches the expansion of a spherical wave formed in the air. Essentially, you want a mechanical Quad ESL. Assuming a large flat panel forming a hemispherical radiation, the sound should travel through the panel at the same speed as the air at 'normal' temp and pressure. The wave speed should constant at all frequencies -- which as a requirement is a doozy.

Needless to say, virtually any bell resonances are going to be distortion. In practice, I'm not sure it's possible to avoid them.

Possibly the worst allegedly hifi speaker I've ever heard was a flat panel driver with a foam core diaphragm, but it would be interesting to see if this sort of thing could be done well. Sounds like CLS has been experimenting for a while, and has gotten some results.
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Old 7th April 2015, 11:24 PM   #26
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Greg B View Post

In theory, the goal should be an expanding wave with an origin at the motor that matches the expansion of a spherical wave formed in the air. Essentially, you want a mechanical Quad ESL. Assuming a large flat panel forming a hemispherical radiation, the sound should travel through the panel at the same speed as the air at 'normal' temp and pressure. The wave speed should constant at all frequencies -- which as a requirement is a doozy.

Hi,

In practise distributed mode loudspeakers don't work like that at all.
The operation is entirely different, and your missing the point entirely.

rgds, sreten.
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Old 7th April 2015, 11:48 PM   #27
kessito is offline kessito  Netherlands
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You could lay the panel flat, put Some sugar on it and look at the Patterns when you play sines at different frequenties. This way you can see were the effectieve placets are to place the blobs for certain frequenties.

Fun!
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Old 7th April 2015, 11:59 PM   #28
xrk971 is offline xrk971  United States
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A Study of DML's as a Full Range Speaker
Quote:
Originally Posted by kessito View Post
You could lay the panel flat, put Some sugar on it and look at the Patterns when you play sines at different frequenties. This way you can see were the effectieve placets are to place the blobs for certain frequenties.

Fun!
I think sand may be a bit cleaner than sugar, and black foam core board may be ideal. They do something similar to visualize drum head modes.

Click the image to open in full size.

A Study of DML's as a Full Range Speaker


You don't want to lay it directly on floor either - suspended at edges with frame or strings.
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Old 8th April 2015, 02:12 AM   #29
freddi is offline freddi  United States
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A Study of DML's as a Full Range Speaker
hey look - from the 1929 Allied Radio catalog 21"x36" version $6.37
Click the image to open in full size.
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Old 8th April 2015, 02:14 AM   #30
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by Greg B View Post
...

Possibly the worst allegedly hifi speaker I've ever heard was a flat panel driver with a foam core diaphragm, but it would be interesting to see if this sort of thing could be done well. ....
The operating principle of DML is simple, however the methods of implementations are varied a LOT, so are the results.

Not many commercial products out there. Here are some of them:

Podium

Teragaki-Labo?????????????????TERRA???????????

Ciresa Opere Sonore : enceintes plates en bois d'instruments

http://www.commbax.com/products/mini...es/minipro.pdf

Professional Distributed Mode Loudspeakers |

I guess it's because of the special acoustic features, it's gradually showing up in pro audio. There must be some pro audio shows where you can see and hear them.
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