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Old 23rd December 2003, 02:42 AM   #1
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Default equations for FR charts

The various loudspeaker books I have show frequency response charts for Qts's of .5, .707, .8, 1.0, 1.1, etc... Can anyone tell me what the formulas are for those charts?
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Old 23rd December 2003, 05:42 AM   #2
Ron E is offline Ron E  United States
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Old 23rd December 2003, 06:56 AM   #3
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Well, the response at resonance can be given by the formula:
20 Log Qts.

So a woofer with a Qts, (or Qtc) of 0.5 is -6 dB at resonance.

I also have a copy of Richard Small's article Loudspeakers in Closed Boxes from the Journal of the Audio Engineering Society on my hard drive. I think the formulas are there.

I can Email it to you if you want.
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Old 24th December 2003, 01:32 AM   #4
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Quote:
Originally posted by kelticwizard
Well, the response at resonance can be given by the formula:
20 Log Qts.

So a woofer with a Qts, (or Qtc) of 0.5 is -6 dB at resonance.

I also have a copy of Richard Small's article Loudspeakers in Closed Boxes from the Journal of the Audio Engineering Society on my hard drive. I think the formulas are there.

I can Email it to you if you want.
I'd love to have a copy. I'm djones at innovativerobotics dot com.

Thanks.
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Old 24th December 2003, 09:40 PM   #5
Ron E is offline Ron E  United States
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Pasted from www.diysubwoofers.org

-------------------------------------------------------------------------
To calculate the frequency response of a sealed enclosure system, you will need to know the following:
Fb = resonance frequency of the system
Qtc = Final Q of the system at resonance


then,

Fr = (F/Fb)^2
dBmag = 10*LOG(Fr^2/((Fr-1)^2+Fr/Qtc^2))

where,

F = frequency (Hz)
dBmag = SPL 1W/1M at frequency F
------------------------------------------------------------

Now you plot dB vs. Frequency and you have your chart.
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