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Old 7th October 2003, 12:59 PM   #1
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Default 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!

JojoD
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Old 7th October 2003, 01:03 PM   #2
Immo_G is offline Immo_G  Australia
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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.
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Old 7th October 2003, 05:41 PM   #3
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Immo_G,

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?

JojoD
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Old 7th October 2003, 05:58 PM   #4
tiroth is offline tiroth  United States
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Yes...you 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?
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Old 7th October 2003, 06:03 PM   #5
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Default pot problem

Hi,

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.

JojoD
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Old 7th October 2003, 06:55 PM   #6
tiroth is offline tiroth  United States
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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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