software for designing passive notch filters


2004-10-11 5:21 pm
is there any good freeware out there for designing simple notch filters, I need someting at about 3.2kHz with a Q of about 4, and would like a nice bit of software that shows me what component values I need.

what are the pros and cons of series and parallel filters for this?
I think, from memory, Jeff's PCDC spreadsheet calculates prototyping values for these things. You can find it at the FRD Group page.

Pros, well, they do what they're supposed to do. You just have to be mindful of the component values, at which frequency band it'll be operating and amplifier safety. You wouldn't want to use a series RLC circuit in parallel with the system if the addition of the circuit means dropping the impedance low enough to give your amplifier a hard time. Parallel RLC circuits in series can also lessen speaker damping. So try these circuits out and see if the pros/cons make a significant difference.

The free application Speaker Workshop ( includes a simple notch filter calculator. Once you have the center frequency you can use the measurement features of the application to optimize the resistor value for Q.

Just one small point. If you are trying to equalize frequency response (and not just imped), then unless your source imped is high, a series network in parallel will not impact driver response.