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Class D Switching Power Amplifiers and Power D/A conversion

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Old 1st November 2007, 03:33 AM   #1
KOON3876 is offline KOON3876
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Default Full Digital Speaker

I made some DAC by
(1) Voltage magnitude and summing. easy, common R-2R DAC.
(2) Analog magnitude and summing. DIY PowerDAC project.

But there are one more way.
(3) Sound pressure summing.

Case A: you have 32768 speaker element. PCM signal is converted to "numbers" of driven elements, and +/- are converted to drive voltage.
Case B: you have 15 speaker element. Element for MSB is driven by +/-Reference V, and Elements for LSB is driven by +/-(1/32768)Reference V. (below 0.03mV)

Both cases are unrealistic. lets merge both..

15 Elements: driven by D14 to D11, "numbers" driven by upper 4 bits. (15 driven to 0 driven)
11 elements: driven by D10 to D0, "voltage magnitude" driven. Reference Voltage to 1/2048 voltage.
(D15 represents + / - drive voltage)

There are 26 speaker elements per channel, so I need 26 small amplifier per channel.
What will happen when 26 2-inch full range speakers are driven by PCM digital signal?
I completely can not imagine frequency response.

This project will require at least...
56 OpAmps
616 Registers
784 Capacitors
72 TRs
112 Diodes
56 analog switch

Kind of crazy project again

(Full Digital Speaker, with multiple voice coil for each bits, were investigated by some university / manufacturer )
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File Type: png dsp02.png (58.1 KB, 1755 views)
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Old 1st November 2007, 05:25 AM   #2
KOON3876 is offline KOON3876
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DAI is same as previous project.
SCK/LRCK/SDATA go to CPLD, then calculated to number magnitude / voltage magnitude signals.
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Old 1st November 2007, 06:26 AM   #3
FrankWW is offline FrankWW  Canada
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This has to be one of the most imaginative things I've ever read on this site.

What sort of physical array have you in mind for these drivers?

I found this after a bit of googling:


These guys seem closest to what you're proposing:
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Old 1st November 2007, 07:11 AM   #4
banana is offline banana  Hong Kong
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I remember when I was still in collage, my professor once have similar idea.

Instead of R2R, he tried the ladder DAC with 16 element speaker array. Sd of each element range from 1S, 2S, 4S.... 16384S.
But he failed to get it work.

I don't know the reason of his failure. But I wondered the frequency spectrum of individual bit would look like.
For example 16bit NOS data, I guess it'll span very wide
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Old 1st November 2007, 10:19 AM   #5
cph2000 is offline cph2000  Denmark
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There was a british company named 1ltd that tried to do what you are doing a number of years ago.

The technology is presently used in some "one speaker surround sound projectors" from Yamaha !

Aura sound maskes some small full range drivers - take a look at madisounds page, they seem to stock them. They look like the Yamaha drivers.

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Old 1st November 2007, 02:32 PM   #6
KOON3876 is offline KOON3876
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Thank you for your interests.

attached is driver array what I am thinking.
It will act like 1(4 bit woofer) +11way(bit split tweeter).

anyway I can try this project about $1200-$1500, please expect my Mickey Mouse
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Old 1st November 2007, 02:38 PM   #7
phase_accurate is offline phase_accurate
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I know that there were attempts to build something like that using delta sigma modulation but I can't remember where I have seen it.
If it "jumps at me" I'll let you know.


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Old 1st November 2007, 02:53 PM   #8
BWRX is offline BWRX  United States
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Ideally, you would want all these drivers to act as a point source, right?

So why not try a pattern where the small drivers are placed in the empty space between the large drivers? I can't draw a picture at the moment but imagine 5 columns of large drivers: 2 on the left, then 3, then 5 in the middle, then 3, then 2 on the right. And in between each of the large drivers is a small driver.
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Old 1st November 2007, 08:31 PM   #9
Pano is offline Pano  United States
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A cool idea, really love it, but there is one big problem.

The nonlinearity of air.

I should know, I started work on this concept about 17 years ago. ( I was not the first). I had a few email conversations about 10 years ago with the guy in England who got venture capital invested in the same thing. He had been written up in some EE journals. Our ideas were very similar, he was at the same crude prototype stage I was at the time. We both used off the shelf ultrasonic transducers.

The problem is trying to get all those elements to generate a waveform in the air that is anything like the input signal. It just doesn't work. Heavy DSP is needed to make it sound right.

Don't know whatever happened to the Brit effort. It may well be in the Yamaha unit, but from what I've read the Yamaha is a little different.

As for me, I never got anywhere much with it. But it did lead me to "Digital" amplification, for which I'm grateful.
Take the Speaker Voltage Test!
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Old 2nd November 2007, 01:58 AM   #10
KOON3876 is offline KOON3876
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Thank you for informations.
I'm not so pessimistic. Please anticipate my Kamikaze attack.

Attached shows 2 wav form, created from "cum on feel the noize" by Quiet Riot. Upper one shows 4-bit, you can see steps. lower is wave form by D10 to D0.

now simulating and I feel Listening point focusing will be important. (same as written in PDF)
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File Type: png separated wave.png (45.5 KB, 1193 views)
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