How do I measure the Qtc and Fsc of an existing subwoofer? - diyAudio
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Old 10th July 2003, 09:57 PM   #1
PUCK is offline PUCK  United States
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Default How do I measure the Qtc and Fsc of an existing subwoofer?

I am building a sub and have used UniBox to do so. I will eventually be adding a Linkwitz Transform to the sub to lower the Qtc and Fsc, but to do this accurately, I would like to be able to measure the pre-Linkwitz Qtc and Fsc of the sub. I can calculate it, but I imagine it may be quite different in reality.

I have a multimeter, oscilloscope, reference mic, signal generator (in computer). How do I do this? And yes, I searched but couldn't find what I needed...

Thanks!
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Old 11th July 2003, 02:07 AM   #2
Ron E is offline Ron E  United States
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http://www.kbapps.com/audio/speakerd...arameters.html


Measured jut like Qts, Fs
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Old 11th July 2003, 03:26 PM   #3
PUCK is offline PUCK  United States
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Unless I'm missing it, those look like links on how to calculate those values.... not measure it.
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Old 11th July 2003, 05:40 PM   #4
Ron E is offline Ron E  United States
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The site apparently doesn't allow linking to frames....

Go to www.kbapps.com

Click on the link "Audio speaker design calculators"
Click on the link "Enter Calculators"

In the instructions page that follows, click on the word "parameters".


If that all seems too hard search on google for
"dick pierce impedometer"
I know it sounds like some sort of urological prosthesis rather than someting about speakers - but it will get you what you need.
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Old 11th July 2003, 05:46 PM   #5
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That's PERFECT!! Thanks so much!
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Old 11th July 2003, 08:05 PM   #6
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Default Measuring impedance plot:

Hi,

For calculating Qt-box ant Fs-box you need to measure the impedance curve of your box first. Here you can download a nifty shareware program that does it for you automatically with the help of your soundcard.

If you measure the impedance curve with the help of your soundcard be sure it is very silent in your room/workshop. Note that your speaker acts as a sensitive microphone too. Sounds picked up by your speaker can blur your measurements.

And here an other picture about how to calculate Fs and Qt from the impedance plot:

http://www.linkwitzlab.com/images/graphics/f0Q0.gif

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