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Low pass filter for subwoofer.
Low pass filter for subwoofer.
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Old 15th January 2015, 09:34 AM   #1
mememachine is offline mememachine
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Default Low pass filter for subwoofer.

Hi all,

I recently acquired a Sony SA-WMSP87 amplifier which has a mono input, and am needing a low pass filter as I currently only have a 3.5mm to rca jack as an input (homemade, joined L/R connections of the 3.5mm cable together and connected to 1 rca cable along with the ground). The subwoofer only has a mono rca input, so I'm looking for something cheap to use as a low pass filter to cut out frequencies >90-100Hz. Would something like this diy board suffice? - NE5532 LOW Pass Filter Subwoofer Process Circuit Frequency Volume FOR Amplifer | eBay

Something like this even? http://www.ebay.com.au/itm/100Hz-low...item1c495a3fb2

If so, how would I safely connect it to the subwoofer over RCA? The source is a HifimeDIY Sabre DAC which puts out well enough power for the sub.

I'm quite new to this stuff so sorry if I'm not being informative enough.

Last edited by mememachine; 15th January 2015 at 10:08 AM.
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Old 15th January 2015, 02:29 PM   #2
Speedskater is offline Speedskater  United States
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It's not a good idea to wye two signals (L&R) to one input. So you will need to add 2 resistors to your filter.

Why Not Wye?
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04

Splitting Signals
Subwoofing in Mono
Unbalanced Summing
Balanced Summing
Output Impedances

Why Not Wye?
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Old 16th January 2015, 12:43 PM   #3
AndrewT is offline AndrewT  Scotland
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use a two input inverting MFB 2pole filter as your SUMMING amp and as your Low Pass Filter.
If you require more than two pole, you can add another 2pole filter stage, either MFB to invert the signal back to normal, or a Salen and Key to keep the inverted signal (to be corrected later, like swapping the speaker leads).
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Old 16th January 2015, 01:30 PM   #4
Buehgemeiste is offline Buehgemeiste
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i own exactly the same board from ebay.
but i donīt use it since i learned how to build active filters.
for home subwoofers a 3rd order mfb filter (18db) should be enough.
here you can calculate your own:
3rd order Multiple feedback Low-pass Filter Design Tool
put an inverting summer in front of it.
a single TL072 opamp is enough for this application.
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Old 16th February 2015, 12:28 PM   #5
tiefbassuebertr is offline tiefbassuebertr  Germany
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Default Syrincs Subcontrol II with variable 4rd order low pass according Sallen-Key

This device is for me the best available low-cost device - actually made for car-hifi, but also good suited for home-audio. variable 4rd or low pass filter and variable subsonic filter are inside. Individual modifications are very easy.
Instruction manual is here:
http://www.syrincs.de/new/manual/mansc2.pdf
schematic, which I have created some time ago is here
Attached Files
File Type: pdf Syrincs Subcontr-II schem.pdf (110.4 KB, 595 views)

Last edited by tiefbassuebertr; 16th February 2015 at 12:37 PM.
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Old 16th February 2015, 12:37 PM   #6
AndrewT is offline AndrewT  Scotland
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That syrincs link is to a commercial device.
There is no schematic, so it cannot be DIY.

What's the point in linking to a user manual of a non DIY device?
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Old 16th February 2015, 12:57 PM   #7
Gopher is offline Gopher  United Kingdom
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Andrew

There is a schematic - see attached file. Maybe he added it.
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Old 16th February 2015, 03:13 PM   #8
AndrewT is offline AndrewT  Scotland
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That's more appropriate. I obviously did not search enough !
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Old 16th February 2015, 08:31 PM   #9
tiefbassuebertr is offline tiefbassuebertr  Germany
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The Syrincs Subcontrol II is out of production (obsolete) and thus only available in used condition. Because of the low cost (between 20 and 70 euros at ebay) a serious alternative to a diy project in most cases.
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Old 16th February 2015, 09:15 PM   #10
tiefbassuebertr is offline tiefbassuebertr  Germany
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another active filter device, which consist also of a low pass and high pass (subsonic) filter is the Hormann AX2:
http://www.hormann-audio.de/viewarti...escription.htm
Who can upload the schematic diagram?

Also of interest is this filter device: Bryston 10B-STD Electronic Crossover
http://www.bryston.com/products/other/10B-STD.html
http://www.bryston.com/PDF/Manuals/300001[10B].pdf
http://www.6moons.com/audioreviews/b...ossover_3.html

My own circuit design looks as follow:
1) summing amp (like syrincs subcontrol II)
2) continue variable high pass, two 12db sections in serial, each 12db a stereo potentiometer (at whole 24db/oct, 4rd order)
3) continue variable low pass, three 12db sections in serial, each 12db a stereo potentiometer (at whole 36db/oct, 6rd order)

Are there such a subwoofer active crossover on the marked in the same kind as the devices above ?

Last edited by tiefbassuebertr; 16th February 2015 at 09:39 PM.
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