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Old 13th March 2011, 10:19 AM   #1
Chendy is offline Chendy  United Kingdom
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Default What does the y-axis of soundfile represent wrt to a loudspeaker driver?

I am interested in motional feedback, but am unsure about a fundamental aspect of audio technology:

We all know the axis of a sound file represents time, but what does the y-axis represent?

I think it represents sound pressure; the desired sound pressure variation to be reproduced at a listeners ears. Due to convention, this ends up relating to voltage from a voltage source.

But what does this y-axis relate to on the loudspeaker itself? Is it displacement, velocity or acceleration? I assume that if the y-axis is the desired sound pressure, then as pressure is proportional to force, and force is proportional to acceleration then the y-axis relates to the acceleration of the loudspeaker driver.



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Old 13th March 2011, 01:49 PM   #2
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Voltage transduces to cone velocity which further transduses to sound preasure.
Current transduces to force and this is a side effect of speaker impedance.
The above is much more physics and much less "convention" of a dynamic speaker than many use to think.
Thus, the motional feedback usually tries to track cone velocity (=integral of acceleration).

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Old 14th March 2011, 09:10 AM   #3
Chendy is offline Chendy  United Kingdom
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Ok, so the voltage is proportional to cone velocity?

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Old 14th March 2011, 01:31 PM   #4
Eva is offline Eva  Spain
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See it the opposite way, the purpose of motional feedback is to make cone velocity (dx/dt) track input signal (voltage(t)) with improved accuracy.
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Old 14th March 2011, 02:10 PM   #5
Pafi is offline Pafi  Hungary
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Quote:
Ok, so the voltage is proportional to cone velocity?
Only the induced voltage, but total coil voltage contains R*I and L*di/dt also, and these are much higher at high freq.

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I think it represents sound pressure; the desired sound pressure variation to be reproduced at a listeners ears.
Yes, this is correct, theoretically at least.

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But what does this y-axis relate to on the loudspeaker itself?
The answer is: nothing. In a dinamic speaker box nothing is simply proportional to sound pressure. There are several different frequency dependent effects, which are compensating each other if you are very lucky. And this is only linear asumption. High-level effect makes it more complex.
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Old 15th March 2011, 05:02 PM   #6
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But for a closed box it's acceleration to get a flat frequency response, at least as long as the speaker driver is small compared to the wavelength and it is working as a piston.

This is what happens in a voltage-driven closed box speaker above its resonance frequency.
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