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Class D Switching Power Amplifiers and Power D/A conversion

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Old 2nd November 2007, 02:29 AM   #11
fdeck is offline fdeck  United States
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For this scheme to work, don't all the speakers need to have the same transient response functions?
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Old 2nd November 2007, 04:50 AM   #12
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At principle, yes.

when sound(y) is represented by
y=G[f(t)],
f(t): original sound wave, represented by FFT
G[]: Speaker responce function

This speaker system's output will be
y' = Sigma[Gk[Hk[f(t - Tk)]]
where
k: Speaker element, 1 to 26
Gk[]: Speaker transient response function.
Hk[]: bit fetch function.
Tk: each speaker's time delay from center point.

When
(1) all Gk[] = G[], all speaker transient is same
(2) Sigma[Hk[]] = 1, this is no problem.
(3) all Tk = 0, all driver has same distance from ear,
y' = y.

I'm not sure about (1)'s importance.
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Old 2nd November 2007, 06:26 PM   #13
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They've been working on digital loudspeakers for a while here in Greece. Check this.
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Old 2nd November 2007, 11:04 PM   #14
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Shaman

Unfortunately they are not writing what will happen when
(1) Traditional one-bit per transducer assignment
(2) Novel PCM word mapping on 2^N-1 array
both implemented. that's what I want to try.
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Old 3rd November 2007, 03:36 AM   #15
fdeck is offline fdeck  United States
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Here is what bothers me. I am thinking of a simple sinewave input waveform. The output to each speaker element is a waveform of the same fundamental frequency as the input frequency. If the different drivers each produce a different phase error at this frequency, then there will be some cancellation. There will be more cancellation due to off-axis effects. So I think the only way this can work is if the drivers are all identical, and you are only listening on-axis.
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Old 3rd November 2007, 04:40 AM   #16
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Today I ordered 60 lot of 2 inch driver

>fdeck

Yes, now I'm thinking how to adjust phase by mm order to listening position.

I revise myself. To think DLA (digital loudspeaker array), it's btter to think about inpulse than sinewave. more simpler.
And bit-per-driver section works in -30dB order, so importance of identical is reduced -30dB. (Gk difference effect goes more smaller, to LSB)
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Old 4th November 2007, 03:28 PM   #17
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This is not a normal speaker anymore, it's a Phased Array Rader....
Phased array can focus anywhere by applying delay / advance for each element. (physically / electrically)

I will make it mechanically to focus on horizontal, 6 ft distance.
(just a spacer for each element to make distance equal)

For auto focusing I need these 2. too much now
(a) 3-dimensional position finder
at least 5 element mic array to analyze hand clapping
(b) DSP to apply delay for each elements
to focus on position found at (a)
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Old 4th November 2007, 06:51 PM   #18
FrankWW is offline FrankWW  Canada
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Could you not get the same effect by arranging them in a circular fashion? (Off axis response might be nicer too. I think that's what the Greeks did).

Quote:
just a spacer for each element to make distance equal
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Old 4th November 2007, 10:00 PM   #19
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"Greeks" means Fotios Kontomichos, Nicolas Alexander Tatlas, and John Mourjopoulos?
They are using tiled array. I have pdf...

Circular fashion goes too large, and distance of diagonal pair will be about 20 inch > twice as arrayed. especially horizontal positioning, it will have too tenderness.
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Old 4th November 2007, 11:38 PM   #20
Eva is offline Eva  Spain
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In the usual listening environment we hear a substantial amount of off-axis sound reflected by walls, floor and ceiling. A good-sounding speaker can exhibit wide or narrow directivity, but it must produce good off-axis sound. This speaker DAC idea is not practical because it produces terrible off-axis output.
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