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-   -   calculating Q for spl due to RLC notch filter (http://www.diyaudio.com/forums/multi-way/149079-calculating-q-spl-due-rlc-notch-filter.html)

Dave R 21st August 2009 12:30 AM

calculating Q for spl due to RLC notch filter
 
Is there such a thing as a "Q" for the notch in spl caused by a parallel RLC filter, and if so is it calculated similar to the Q for the notch in the impedance? I can't seem to find this defined anywhere.

Numbers below are for example only.

freq atten
(Hz) (dB)
---- ------
6184 -2.00
7039 -2.83
9016 -4.00 << (notch center freq)
11548 -2.83
13145 -2.00

Is it simply calculated at the point where the attenuation is .707 x SPL@ notch?

In this case where atten = 4.00 x .707 = 2.83, I'd be inclined to calculate Qspl as follows:

Qspl = [9016/(11548-7039)] = 2.0

What I'm leading toward is trying to size up the RLC values for a notch filter, when the Q for spl can be obtained from measured data.

Dave R
the 200% Norske

infinia 21st August 2009 12:58 AM

Q is defined for any second order system response ie any RLC. So you would measure it the same way for a speaker driver or a sallen key filter stage. Q = central freq /half power BW


Hint use 3 dB away from central point not 0.707
If meas. using voltage then 0.707 is correct.
Vp=1 V then 20log*1/0.707= 3 dB

Ron E 21st August 2009 04:59 PM

1 Attachment(s)
Quote:

Originally Posted by Dave R (Post 1903881)
Is there such a thing as a "Q" for the notch in spl caused by a parallel RLC filter, and if so is it calculated similar to the Q for the notch in the impedance?

See attached. Have fun.

Dave R 22nd August 2009 01:56 PM

Thanks Ron. Nice little spreadsheet. :)


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