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Have we discussed this tech already?

DonH56

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#2
I was thinking I saw this well over ten years ago, then saw the company has been around since 2006... There have been a number of companies that have tried this approach but AFAIK none have been successful. I proposed something similar when I first did some MEMs-focused work ca. 199x (I think) but didn't get a hit on the proposal. It is a neat idea but apparently with a lot of practical roadblocks, as evidenced by their financials ( http://www.audiopixels.com.au/index...-announcements-2017/preliminary-final-report/ ). I can think of a number of technical challenges, but since my MEMs knowledge is limited I'll just say I remain intrigued but skeptical. I thought DLPs taking off might have bolstered speakers based on MEMs but seems there is still a ways to go to make them practical.
 

RayDunzl

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#3
What speaker devices are cell phones using now?
 

DonH56

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#4
Still conventional microspeakers AFAIK. That is, they work like regular speakers more-or-less, but are very small. No MEMs.
 

RayDunzl

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#5

Cosmik

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#6
I'd like to know what size panels of these things you'd need compared to the average woofer, mid and tweeter. I glean that they use a PWM scheme to move a tiny diaphragm that, presumably only has a tiny displacement. Do we need to cover the wall in order to get decent SPLs?
 

DonH56

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#7
@RayDunzl -- Yes, I think those are conventional microspeakers. Some use piezoelectric drivers. Not MEMs.

@Cosmik -- One of the fundamental issues. Like planar designs (ESLs, planar dynamics), displacement is limited, so you need a lot of them (large area) to achieve high SPLs. A lot means high yield, high cost, etc. And it takes a bit to drive them all since you are generating enough field strength to deflect a mechanical beam (beam like on a teeter-totter, not like an EM or optical beam) on a whole lot of them at once. They can also be delicate and with finite lifetime due to essentially mechanical wear. I think, not claiming to know all that much about MEMs.

One scheme I vaguely remember used a carrier approach, many MEMs (or other drivers) oscillating with the array modulated to produce interference patterns that produced sound. The implications for programmable beam forming, dispersion characteristics, etc. are interesting. One claim was that they could "place" the sound at a specific place in space and away from that you might hear nothing or noise. Never heard if it went any further and a job change took me away from those sort of research articles so I've not kept up.
 

Brad

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#8
The wear of MEMS is generally not a consideration. Have you ever heard of a DLP chip wearing out? They oscillate at several 100kHz
They claim that the chips achieve a much better impedance match to the air, hence large areas like ESLs are not necessary.
Has anyone read how this improved impedance is achieved? My guess is that it has something to do with the high frequency oscillation of the chips enabled by using PDM to create the desired output.
 

DonH56

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#9
Yes... But it takes a while. MEM switches I have researched have generally impressive but varied lifetimes.

As I said, I am not a MEMs expert. The description indicates pulse modulation and sort of implies a carrier but I'd have to dig deeper (and unfortunately have other commitments right now). They claim 10x-60x the performance/sensitivity of conventional speakers, but ultimately still use a vibrating surface coupled to the air. Switching the MEMs requires voltage and they could certainly provide a high-impedance load to the driver, but to improve coupling to achieve the higher SPL from a smaller area makes me think they are doing some sort of carrier modulation scheme or pulsed-power (pressure wave, actually) implementation. They have impressive claims and I have seen similar claims with the results to back them up in the past. I can't remember exactly the technology; their descriptions are tantalizingly familiar but it was a long time ago. There was a technology that set up standing waves that were modulated to create sound (like mixing in an RF system to create audible frequencies). I think. The trick was to make them commercially viable, something that seemingly has not happened yet. Their report indicates they are moving into Phase 4 of their long-range plan so hopefully commercial products aren't too far out. Takes a long time to work through all the roadblocks...

I'm over my head on this one, sorry. Not a technology I am really familiar with so this is all guesswork on my part.
 

amirm

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#10
Has anyone read how this improved impedance is achieved?
I suspect that is due to very small area of the mems "pixel." Easy to push the end of a pin through air than a sheet of paper.
 

Brad

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#12
Could you be thinking of the ultrasonic systems that beat two beams together that downmix in the ear?
Those systems are used for localised sound. I believe the smithsonian uses such a system
 

Don Hills

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#13
I suspect that is due to very small area of the mems "pixel." Easy to push the end of a pin through air than a sheet of paper.
That's a very poor impedance match, not a good one. The piece of paper is a much better match - remember, you need to match the mass of the thing doing the "pushing" to the mass of the air being pushed.
 

Brad

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#14
That's right, you want to be in a regime with the air (fluid) acts more like a solid. My suspicion is that at very high frequencies this may be the case.
Hence, a pulse density modulation (like DSD, or sigma-delta modulators) can push/pull the air at high frequencies, but still create audio tones
 
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