Speaker's Fr variation with signal level - Page 4 - diyAudio
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Old 5th August 2005, 04:38 PM   #31
gpapag is offline gpapag  Greece
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All the above measurements (Vas, Q and past Fs measurements) show results that are approaching the published specs when the excitation signal is at a higher level (>400mV RMS). The lower test signals (especially below 100mV RMS) show results far away from the published data and at the same time quite sensitive to small signal variations. This, together with the fact that listening levels are produced by a signal of not less than 300mV RMS on these speakers, makes me choose the higher signal level characteristics, these of around 500mV RMS.

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George
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Old 5th August 2005, 05:15 PM   #32
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by gpapag
Hi all
I took the time to do some more manual measurements to check for any change occurring to Q and Vas of the JX92S relative to excitation signal.
Results below:
Vas increases across the full span of applied signal.
How do you determine VAS? This is not directly measured.
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Old 5th August 2005, 08:43 PM   #33
gpapag is offline gpapag  Greece
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Quote from soongsc:"How do you determine VAS? This is not directly measured."

Vas is determined using the closed box method. An unstuffed closed box with volume Vb<Vas/2 is used:
1. Measure Free air resonance freq. of driver (fs)
2. Measure In-Box resonance freq. of driver (fct). Both measurements with exactly the same signal amplitude
3. Calculate Vas=1.15[(fct/fs)^2 -1]Vb

Method is referenced in Vance Dickason “Loudspeaker Cookbook” fourth Edition pages 131-132 and David Weems “Great Sound Stereo Speaker Manual” first Edition page 208

Vas data as well as Q data and Fr data at the attachment. (Color at the columns represent: Blue=Set data, Yellow=Measured data, Green=Calculated data).

Regards
George
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