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Old 9th December 2009, 07:41 PM   #1
MCPete is offline MCPete  United States
diyAudio Member
Join Date: Nov 2005
Default Where to measure max. input voltage to woofer

This is all about experimentally testing Small's formulation that

Per = Par/ No


Per = displacement-limited (maximum) power
Par = displacement-limited acoustic power rating
No = eta or efficiency

Small also defines Pe as input electrical power where the impedance of a driver is considered to be the dc resistance of the driver Re. Then

Vi(max) = sqrt(Per*Re)

where Vi(max) is the rms voltage at input to the driver causing diaphragm displacement of the driver to equal Xmax.

So let's say that I have a two-way closed-box system with a passive crossover network. I'll measure the peak displacement of the woofer's cone of the system when electrical power at input is that which should cause that displacement to equal Xmax. The input signal will be pink noise as pink noise has power density distribution that is roughly equivalent to that of music.

My question is, should I measure Vi(max) at the input terminals to the speaker system or across the voice coil terminations of the woofer? As there is the low-pass filter between the system input terminals and the voice coil of the woofer, these two voltages will be substantially different.

Sorry about thinking up this stuff. Have a great day.
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