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Old 11-13-2018, 11:44 AM   #1
brainwreck
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Default Any experience with Distributed Mode Loudspeakers (DML)?

I'm just wondering if any of you have any experience with DML speakers, and if so, what your impressions are of the approach. From what I have seen so far, it seems like a DML speaker design could possibly be useful for both monitoring and mixing as well as live sound.

If you never heard of this style of speaker, the basic idea is using an exciter (a speaker voice coil) to vibrate a panel. Like this: https://www.youtube.com/watch?v=VS0mClcl56g&t=4m52s

And the benefits of DML speakers are said to be: wide dispersion (omni pattern) across the capable frequency spectrum (don't produce low frequecies well, though), low interaction with room modes, high resistance to feedback, low cost to produce, and physical flat/lightweight design.

There seems to be a larger diy community around DML experimentation and design than a commercial market up to this point although there are some companies selling DML speakers. Here is a playlist from a company called Tectonic on the benefits of DML speakers: https://www.youtube.com/playlist?lis...9rr5pXNwD-2GMr
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Old 11-13-2018, 12:40 PM   #2
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There is a presentation and demonstration of using various panel materials for DML speakers here: https://www.youtube.com/watch?v=CKIye4RZ-5k

At 15:05 is some audio analysis comparisons of varioius panel materials.

At 32:50 is a demonstration of using various panel materials together and various music playback demonstrations.
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Old 11-13-2018, 06:25 PM   #3
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Nothing new under the sun, I'm afraid.

In the 70's there was a brand of speakers, I think BNS, that produced flat panel speakers based on this principle. They were made from styrofoam in an wooden frame. Sounded not too bad, but didn't sell.

There might be a potential patent problem. In the 90's, some company developed an auto eq correction system for this kind of application. They even signed up some customers, like a very big Japanese glass manufacturer and made lots of noise about windows that would act as speakers. No products ever surfaced, AFAIK. Dunno what happened. The system was digital and required a fair bit of CPU power. Maybe that was a problem? Anyhow, they had patented that stuff and that usually prevents others going down the same path...
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Old 11-13-2018, 09:34 PM   #4
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Given the low cost and the relatively decent sound quality, it seems it would be a pretty good and inexpensive way to get an ambisonic array set up. As one of the videos mentioned, the response below 100 Hz is pretty poor, but a subwoofer would handle that task pretty well.
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Old 11-14-2018, 05:47 AM   #5
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Quote:
Originally Posted by brainwreck View Post
There is a presentation and demonstration of using various panel materials for DML speakers here: https://www.youtube.com/watch?v=CKIye4RZ-5k

At 15:05 is some audio analysis comparisons of varioius panel materials.

At 32:50 is a demonstration of using various panel materials together and various music playback demonstrations.
The measurements are a complete joke. The distance from the back wall is less than the distance from the measuring microphone, this will result in all kinds of reflections interfering with the direct sound. This interference will be dependent on the size and shape of the radiator thus preventing any meaningful conclusion about the differences of the panel material.
The way the microphone is mounted on the stand is also wrong, it should be straight and with a reflection free mounting.
From what I've seen (and measured myself) the response is far from flat, the cumulative spectral decay(CSD) looks like crap and the directivity is far from smooth. I don't see how these units can be used for quality sound reproduction.
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Old 11-14-2018, 09:50 AM   #6
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Quote:
Originally Posted by Gerrit View Post
The measurements are a complete joke. The distance from the back wall is less than the distance from the measuring microphone, this will result in all kinds of reflections interfering with the direct sound. This interference will be dependent on the size and shape of the radiator thus preventing any meaningful conclusion about the differences of the panel material.
The way the microphone is mounted on the stand is also wrong, it should be straight and with a reflection free mounting.
From what I've seen (and measured myself) the response is far from flat, the cumulative spectral decay(CSD) looks like crap and the directivity is far from smooth. I don't see how these units can be used for quality sound reproduction.
It looks like that guy is at least attempting to address testing criticism: https://www.youtube.com/watch?v=fqodnHxRJ7c
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Old 11-14-2018, 10:29 AM   #7
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Quote:
Originally Posted by brainwreck View Post
It looks like that guy is at least attempting to address testing criticism: https://www.youtube.com/watch?v=fqodnHxRJ7c
This guy obviously never heard of quasi-anechoic measurements as there is no impulse response to be seen anywhere.
What you normally do is keep away from reflective surfaces as far as possible and then remove the part of the impulse response after the first reflection thus you end up with a 'quasi-anechoic' response. The trade off is in the frequency resolution, increasing the distance from reflective surfaces will increase the resolution and simultaneously decrease lowest measurable frequency.
See this post on Tweeter Measurements for details on the importance of a proper microphone mount. Notice that the legend below the diagrams tells you the parameters of the measurement, most importantly the FreqLO which is the resolution and lowest measurement frequency.
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Old 11-14-2018, 11:31 AM   #8
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Quote:
Originally Posted by Gerrit View Post
This guy obviously never heard of quasi-anechoic measurements as there is no impulse response to be seen anywhere.
What you normally do is keep away from reflective surfaces as far as possible and then remove the part of the impulse response after the first reflection thus you end up with a 'quasi-anechoic' response. The trade off is in the frequency resolution, increasing the distance from reflective surfaces will increase the resolution and simultaneously decrease lowest measurable frequency.
See this post on Tweeter Measurements for details on the importance of a proper microphone mount. Notice that the legend below the diagrams tells you the parameters of the measurement, most importantly the FreqLO which is the resolution and lowest measurement frequency.
I never heard of it either. Can you elaborate on this part a bit?

Quote:
The trade off is in the frequency resolution, increasing the distance from reflective surfaces will increase the resolution and simultaneously decrease lowest measurable frequency.
By 'decrease lowest measurable frequency' do you mean that the lowest measurable frequency gets better or worse? I think you must mean, capable of measuring lower frequencies. Just clarifying.
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Old 11-14-2018, 12:43 PM   #9
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Quasi-anechoic measurements are used for evaluating drivers and or complete systems without the room interfering. A computer based system is needed for this. The signal (either MLS or Log chirp) is used to calculate the impulse response. Here's an example from the post on Tweeter measurements:



The large peak is the direct signal. At about 8ms there's a strong reflection. The part of the impulse response that is used is shown in black, start at 1.27ms end at 4.34ms. This part is free of any reflections, the room could be made of marble or foam it doesn't matter. The length of the impulse response corresponds to a frequency of 326Hz (FreqLO in the legend), this is the measurement resolution. Peaks or dips that are narrower than 326Hz will be smoothed or not captured at all with this measurement. Frequencies lower than 326Hz will not fit in the impulse response window and thus cannot be measured.
If you look carefully at the frequency response you'll notice that the details increase as the frequency increases:


Although it says 'unsmoothed' in the legend a resolution of 326Hz means that between 1kHz and 2kHz (one octave range) there's actually 1/3 octave smoothing applied.
So the trick is to keep away from reflective surfaces as far as possible so the impulse response window can be as large as possible.
Arta is a popular, inexpensive software package for audio analysis that works with any decent audio interface.
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