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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 6th April 2015, 04:22 PM   #11
CLS is offline CLS  Taiwan
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Several suggestions:

1. Bigger is better

2. Rounded corners (or irregular shapes) can help diffusing edge reflections. Think water tank - ripple experiment. Your added masses act like some stones along the banks, also diffuse the wave effectively. As you can see the effects vary a lot.

3. Foamcore board is light, so it's easily damped. Constrained layer damping can be applied locally around edges. I've try felt pads and they work well. See Manger's bending wave unit.

4. Foam is soft and can eat some vibration energy from the exciter. On such material, driving the front surface of the panel helps a lot in HF. Refer to the following sketch:

Click the image to open in full size.

Cut a shallow hole and retain the front surface paper. Fill the hole with some other dense material - solid cardboard, plywood etc. So the exciter is now driving the front surface more directly, instead of riding on the spongy rear surface.

One step further, the dimension where exciter drive the board affects the highest frequency. My little exciter has 1" VC. The driving ring is about the same size. It can play up to 20kHz on proper panel.

If the rigid 'transmission' can be built in a smaller size, theoretically the HF can be even higher. Like the one on the right.

5. For the low end, in addition to bigger panel area, you'd need higher driving force. A powerful exciter, or multiple smaller ones.

6. Heavy 'panel' like framed glass can work. (or, every surface can) The main problem is the resonances could be too strong and hard to control.

I've also tried this. The glass is fix on a dry wall. So the exciter on glass is actually driving the glass and the whole wall. There's a huge peak at 32Hz, and other irregularities in frequency response here and there. Very amusing effect, but impossible to deal with those problem physically. Severe EQ is needed.

This is hugely fun, and has the potential of very good sounding by very cheap devices and materials, but a LOT of experiments are needed.

Last edited by CLS; 6th April 2015 at 04:25 PM.
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Old 6th April 2015, 04:28 PM   #12
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by Elias View Post
Where is a directivity plot ?

Then we'll know how usefull is this concept


.
It's almost omni in the room. Or very wide bipole with very narrow null at the sides.

It's not dipole as the appearance suggests.
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Old 6th April 2015, 04:35 PM   #13
Omholt is offline Omholt  Norway
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A Study of DML's as a Full Range Speaker
Why would anyone want omni direction in a small room?
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Old 6th April 2015, 04:57 PM   #14
xrk971 is offline xrk971  United States
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A Study of DML's as a Full Range Speaker
Thanks for the great tips CLS. Bigger is better - as I noticed after cutting my 20x30 down smaller. The hard "puck" behind the driver seems to be a good trick for more HF's. Will try that. I am glad there seems to be interest in this thread.
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Old 6th April 2015, 06:46 PM   #15
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Elias View Post
Where is a directivity plot ?

Then we'll know how usefull is this concept


.
Yes, planning on getting the polar data soon. From listening to it and walking around - it does sound semi-omni as CLS suggests with a very narrow null rights at the edges. It is not a dipole though.
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Old 6th April 2015, 06:47 PM   #16
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by BYRTT View Post
Thanks sharing very interesting.

Maybe stupid but could a exciter or more exciters exchange those 6,5" woofers on your trynergy build or even make the four insides in a Synergy horn vibrate with exciters instead of cone drivers.

Click the image to open in full size.
Picture linked from Trynergy thread found here http://www.diyaudio.com/forums/full-...x-synergy.html.
Neat idea - I was also thinking of the same thing too...
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Old 7th April 2015, 02:33 AM   #17
CLS is offline CLS  Taiwan
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I could be wrong, but it doesn't feel right to load a DML with horn (or WG).

The driver of DML works in high velocity, while horn driver works in high pressure.

Waveforms in a horn need to be tidy, planar or sphere, as perfect as possible. But the radiation of a DML is, well, a total chaos.

About the radiating pattern, there have been many debates already. Wide and narrow dispersions have each own sets of merits and drawbacks.

For commercial products, Elac 4pi tweeter and MBL 101 sound very good to me. So, why omni? I'd say why not?
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Old 7th April 2015, 03:26 AM   #18
bwaslo is offline bwaslo  United States
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A Study of DML's as a Full Range Speaker
I'm surprised no one has tried to use the drivers of these to try to make Walsh type speakers.

What is the effect of driving two units on the same panel in reverse polarity?

Or sticking pins through the foam board in places (perhaps adding a dot of glue to both sides where it goes through paper)? Could that be used to 'tune' the coupling between front and back?
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Old 7th April 2015, 04:41 AM   #19
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by bwaslo View Post
I'm surprised no one has tried to use the drivers of these to try to make Walsh type speakers.
There is.

http://www.diyaudio.com/forums/plana...revisited.html

Quote:
Originally Posted by bwaslo View Post

What is the effect of driving two units on the same panel in reverse polarity?
Since there're many (vibrating) modes across the whole area, so different polarity on the drivers is at least not harmful.

There're inevitably interferences among multiple drivers on a single panel. So it's advisable to spread them in a manner of different distances from each other.

This is the latest panel I built:
Click the image to open in full size.

As can be seen, there're 5 exciters on it. Only the central one see the full voltage of the amp, and in normal polarity.

The two at top and bottom are wired in series, and both in - polarity.

The two at left and right are also in series and - polarity, and further attenuated by a resistor.

All these were driven by a stereo amp, with the central one on one channel, and other 4 on the other. Inputs of both channels see the same signal.

That's the way I wired them, and it was very good right at the beginning. So I didn't make any change.

Sticking pin(s) through different layers should be a great idea. I haven't tried such technique myself, but would expect great results. I think this would work very well on corrugated cardboard, too.


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.

Last edited by CLS; 7th April 2015 at 04:49 AM.
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Old 7th April 2015, 10:27 AM   #20
xrk971 is offline xrk971  United States
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A Study of DML's as a Full Range Speaker
I was thinking along the same lines of reproducing instruments by making foam core violins and cellos, and perhaps a piano soundboard. Putting transducers on the "ensemble" and listening to my own chamber orchestra. CLS pointed out a neat web page on the digital piano thread with similar ideas:
The Hybrid Piano – Part 1 - NCF Music!

I have a cello and violin at home - perhaps put these guys on the sound board near the bridge and listen?
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