Series notch mystery

[Klimon]

Hello,

I'm in need of a notch to filter out a peak (or rather a mountain) from 800-2000hz with summit at 1350hz (+14db!). The textbook solution would be a parallel notch filter (online calculators plenty), then finetuning by ear/ measurement.

However I've noticed that many designers tend to use a series notch filter (the textbook solution for damping impedance at resonance frequency) for exactly my purpose (taming midrange peaks). These filters mostly consist only of L and C using the L's resistance for R. I'm keen to try such a series notch to tame my woofer (I suspect this type of filter to sound better than parallel notches, otherwise why would several designers with 'pedigree' use them) but can't locate any calculator. The generic series notch calculators give high values for R so that using L with similar resistance is impossible. Can anyone direct me to the formula or a calculator to calculate this type of R-less series notch filters?

Cheers

Simon

[sreten]

Hi,

Try a circuit simulator with Re and Le of the driver. e.g. free :

http://focus.ti.com/docs/toolsw/fold...t/tina-ti.html
(just stick an unconnected op-amp in the page corner).

The textbook solution for a notch below a low pass crossover point
is series and for a notch above the low pass crossover point parallel.

/sreten.

[Eton]

Series notch filter is only used on tweeter and rarely on midrange
and never on woofers . it's used only to control the impedance peak present at the resonant frequency (Fs) of a speaker.

[Ron E]

Originally posted by Eton
Series notch filter is only used on tweeter and rarely on midrange
and never on woofers . it's used only to control the impedance peak present at the resonant frequency (Fs) of a speaker.

Series notches CAN be (and ARE) used on ANY speaker. For midrange and tweeters they are perhaps more commonly used as a resonant (impedance) peak filter - this last is what the newbie books will tell you, anyway.....

[Klimon]

Series notches CAN be (and ARE) used on ANY speaker.

Definitely

Try a circuit simulator with Re and Le of the driver. e.g. free :

thanks Sreten, just downloaded the program but it's late and looks complex now (there are nice beers in Belgium)

Cheers,

Simon

[Cal Weldon]

I use them for attenuation. Anyone else?

[sreten]

Originally posted by sreten


The textbook solution for a notch below a low pass crossover point
is series and for a notch above the low pass crossover point parallel.

Note that the series filter has all components in parallel, and the
parallel all components in series, easy to confuse the terminology.

For a tweeter high pass a parallel notch is common below the c/o point
to control its impedance peak. On bass/mids a parallel notch can be
used to control peaks in the stopband. For most other cases response
shaping notch circuits are in series with the driver.

/sreten.