What should be included in a subwoofer lowpass filter? - diyAudio
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Old 3rd February 2013, 06:19 PM   #1
JanErik is offline JanErik  Finland
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Default What should be included in a subwoofer lowpass filter?

I am about to design an adjustable lowpass filter for subwoofer, including these features:

- Summing both incoming channels after buffers
- Sallen-Key for easily adjustable crossover frequency, 24 dB/octave. Would you use trimmers/potentiometers or just jumpers (maybe four selectable frequencies)?
- Differential output for easy inverting and bridging.

Is phase correction necessary?
How about subsonic filter even if I dont play vinyls? Maybe doesnt have to be very steep?
What do you think about this circuit: P48 Sub-Woofer Controller (Rev-A) ?

Last edited by JanErik; 3rd February 2013 at 06:23 PM.
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Old 3rd February 2013, 06:32 PM   #2
tinitus is offline tinitus  Europe
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Originally Posted by JanErik View Post
....adjustable crossover frequency, 24 dB/octave.

Would you use trimmers/potentiometers or just jumpers......
I'm planning to try a bigger main board, with power supply
and small ad-on crossover boards with print connectors
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Old 4th February 2013, 03:53 AM   #3
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i've building my sub, for now it has a low pass filter, a pot for volume control and a parametric eq for correction of room gain, and maybe a preamplifier
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Old 27th March 2013, 08:10 PM   #4
JanErik is offline JanErik  Finland
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I am now finalising the circuit and starting to draw a PCB. It will be adjustable to the extent of replaceable resistors in IC sockets, not by trimmers. The subsonic filter will be simplified with only 6 dB/octave

But is a phase control necessary or would a simple invert switch be enough? Perhaps the phase control also does more harm than good? I have been looking at this: Project 103 - Subwoofer Phase Controller .
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Old 27th March 2013, 08:28 PM   #5
DaveG is offline DaveG  United States
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maybe put the phase adjust circuit on a separate board, so it can easily be switched in or out, or replaced with another try altogether.
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Old 28th March 2013, 11:03 AM   #6
AndrewT is offline AndrewT  Scotland
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DIP sockets for swappable capacitors.
Keep the resistors fixed to maintain your designed DC offsets and noise and gain and stability and Q all at the required values.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 31st March 2013, 02:03 AM   #7
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Another approach would be to make a true crossover network incorporating the high-pass characteristics of the "satellite" speakers. See Siegfried Linkwitz for details. Phase corrections and such are bandaids, and a defined crossover is just as easy to do for DIY.

All good fortune,
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