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Old 10th August 2014, 04:27 AM   #1
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Default How about this sub crossover filter?

I wish to use this circuit. The frequency range will be 40~180 hz adjustable.
I will need to do some changes. But is this a good circuit?
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File Type: pdf SW-100 filter.pdf (21.5 KB, 60 views)
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Old 10th August 2014, 05:15 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

Is it a good circuit ?
No, its appallingly/cluelessly a bad circuit.
You should have some idea that is the case.

rgds, sreten.
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Last edited by sreten; 10th August 2014 at 05:30 AM.
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Old 10th August 2014, 06:09 AM   #3
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This is what it does:

First stage -3dB at 15 Hz and 31Khz midband gain 10

second stage -3dB about 66Khz midband gain 13.6

third stage ( 12dB/octave) LPF -3db at about 52 Hz LF gain 1

fourth stage ( 12dB/octave) pot at min 82Hz -3dB and at max 8.3 Hz

fifth stage ( 6db/octave) LPF -3 dB at about 345 hz

This must be dedicated to ( or part of ) some system. Can't be sure why the designer used so many stages. As it is, it doesn't look OK.

You need to pick the sections that you need and will need to adjust the component values.
What is your maximum input signal level ? What is the input signal level required by your sub amp for full output. What range of frequency control do you need. R10 on the diagram could be wrong. It appears that it should have been 5.6 K. Something wrong there. Why would it need to go down as much as 8.3 Hz ?

All of this is just adding standard circuit blocks to achieve what you want. Why don't you rig one up according to your real need?
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Old 10th August 2014, 07:49 AM   #4
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Thank u very much Ashok & Sreten.
Now need to look for other good circuit.
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Old 10th August 2014, 11:55 AM   #5
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You have only stated two requirements.
1. Variable Fc 40 to 180 Hz
2. Variable level control.

What is the signal source ? Preamp level ( maybe 250mV to 2 Volts! ) or in Volts from speaker leads of the power amp !
Are you looking for a 12dB/octave or 24dB per octave crossover ?
Apparently you don't need signals for the main speakers minus the sub signal.
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Old 11th August 2014, 05:22 AM   #6
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Quote:
Originally Posted by ashok View Post
You have only stated two requirements.
1. Variable Fc 40 to 180 Hz
2. Variable level control.

What is the signal source ? Preamp level ( maybe 250mV to 2 Volts! ) or in Volts from speaker leads of the power amp !
Are you looking for a 12dB/octave or 24dB per octave crossover ?
Apparently you don't need signals for the main speakers minus the sub signal.
The signal source will from any line out of amplifier. Say 1 V.
12 db/octave will be ok.
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Old 11th August 2014, 03:12 PM   #7
Pyramid is offline Pyramid  United States
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The attached schematic will give you a ~45Hz to 182Hz LPF, Butterworth response, -12dB/octave. If you want variable level control, replace the 100K resistor at the input with a ~20K pot (input to high side, output to filter on the wiper).
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File Type: pdf LPF 45-182 Hz.pdf (20.6 KB, 21 views)
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Old 13th August 2014, 08:35 AM   #8
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You will need an input buffer as the filter requires a low source impedance . A buffer ensures that. Additionally a buffer can be used to adjust the signal level. An inverting am can give less or more than unity gain.
In your case 1 V in and 1 V out requires no gain.
It's advisable to use a LR 24dB roll off because you don't want any trace of bass voice etc. coming through the sub. It can be made up of two sections. With fixed resistors it is easy. With two stages you need a 4 section pot. you can even use a switch with fixed frequencies determined by resistors. Maybe a better idea. Read up on LR filters on the ESP web site.
Linkwitz-Riley Electronic Crossover

You can make something like this. Component values are not what you want.
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Old 13th August 2014, 06:00 PM   #9
Pyramid is offline Pyramid  United States
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To build on Ashok's idea, the attached diagram has values for a 4 pole -24dB/octave tunable filter from 40-180Hz. The top diagram is for Bessel response, the bottom for Butterworth.

I added an extra inverting stage on the output to restore the phase that got inverted on the input.
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File Type: pdf 40-180 LPF.pdf (44.9 KB, 13 views)
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Old 13th August 2014, 07:28 PM   #10
Pyramid is offline Pyramid  United States
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Correction to my last post (too late to edit).
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File Type: pdf 40-180 LPF Rev A.pdf (44.9 KB, 19 views)
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