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Calculating phase - MJK?
Calculating phase - MJK?
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Old 18th December 2010, 09:05 PM   #1
Dave Jones is offline Dave Jones  United States
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Join Date: Jul 2003
Location: Silicon Valley
Default Calculating phase - MJK?

I do not know how to calculate the theoretical phase response of a loudspeaker, and it's driving me nuts.

For example, I know that the amplitude response for a closed-box loudspeaker is given by the transfer function,

H(s) = s^2/(s^2 + s/Qtc +1)

Okay, I calculate Qtc and fc for the driver/box combination, and then for a range of frequencies x, I plug i*x/fc into the formula.

Amplitude = modulus( H(i*x/fc) )
Phase_response = degrees(phase( H(i*x/fc) ))

The amplitude chart comes out perfectly. But the phase is all wrong. It approaches zero as frequency grows. That's not surprising when one considers that H is also the transfer function for a second order high-pass filter. But phase charts for loudspeakers do not look like that. Below is a phase chart from MJK's Mathcad program, and the one that I get. Way different.

What's the trick? Martin?
Attached Images
File Type: png mjk-spl.png (7.2 KB, 54 views)
File Type: png my-spl.png (7.3 KB, 55 views)
Davy Jones

Last edited by Dave Jones; 18th December 2010 at 09:10 PM.
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Old 20th December 2010, 06:37 PM   #2
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
Is the difference simply a time delay?
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