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JojoD818 7th October 2003 12:59 PM

Need adjustable LPF for sub...
Hi everyone,

I am looking for a low pass filter circuit that has an adjustable crossover frequency from about 40Hz to 150Hz. It will be used for a sub project, I already have the summing buffers and phase reversal circuit. Can a 12dB Linkwitz-Riley (hope spelling is correct) be setup to be adjustable using dual pots? Anyway, it doesn't matter what alignment it is as long as it has an adjustable frequency.

Thanks in advance!


Immo_G 7th October 2003 01:03 PM

Yep you can use pots, i've got a highpass here, 12dB linkwitz. Used a combo of a pot and a resistor to give me about 70-150 hz adjustable, to filter lower bass out of midbass speakers.

JojoD818 7th October 2003 05:41 PM


I see my idea has already been tested and works. How about using two 12dB LR filters in series? One is fixed at 150Hz while the next filter has a pot and resistor that makes it adjustable from 40-150Hz? Do you think it's worth it?


tiroth 7th October 2003 05:58 PM may well need the sub to roll off a lot faster than 12dB/octave. Why not make both adjustable if you think you will really need it?

JojoD818 7th October 2003 06:03 PM

pot problem

I forgot to mention that 4 gang pots are not available anymore at shops here. Only dual gang pots are available, I don't want to adjust the sub frequency using 2 pots. :D


tiroth 7th October 2003 06:55 PM

Give it some thought. Even though the two pots won't track exactly, it could be useful. If you are crossing at 60Hz that 150Hz fixed frequency pole won't help in that critical transition region. Mismatched poles at 60 and 70 would though. You know your application though so if a simpler solution works, by all means go for it.

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