Need advice isolating subwoofer channel from main L/R channels. - diyAudio
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Old 14th March 2012, 05:17 AM   #1
diyAudio Member
Join Date: Oct 2011
Default Need advice isolating subwoofer channel from main L/R channels.


I have a fairly nice sounding setup with a nice dual mono block amp with huge torroidal transformer, homemade preamp with stereo scraper pot, and a decent sounding affordoble DAC (fiio d3), infinity rs-2001 reference bookshelf speakers / studio monitors.

The infinities with this setup sound REALLY awesome with strong bass all the way down to 60hz. However, I need just a bit more bass and so I purchased a Polk Audio PSW505 12" subwoofer and when hooked up it really provides the bass missing from the infinities.

However, the highs and mids don't sound as clear on the infinities when I have the sub hooked up, because I am splitting the audio signal within my preamp with a hard wired Y splittler (dedicated stereo outputs on back of preamp for sub).

I unplug the sub from the back of my preamp and the infinities just sound worlds better.

So I am trying to think of a way to use this subwoofer with my system without sacrificing any sound quality and came up with the following idea. Please let me know what you think :

Get another FIIO D3 dac and feed the digital signal into it from the analog digital signal from the other dac (kinda wire them together inside the preamp-- yeah they are small enough to easily fit inside my pre.. I already have one inside it.)

Anyways so my computer provides the digital signal via fiber to the first dac and the second dac gets the electrical digital signal from the board of the first dac. Assuming they both are designed the same and have the same exact latency they would output an exact copy of the analog signal for each channel at the same exact time. Then feed these four signals into a stepped 4 (or 5.1) channel volume potentiometer. Then one pair of channels go the amp and the other go to the sub.

If I did this shouldn't I have the same sound quality I have on my infinities now with the sub unplugged?

Maybe I am over-complicating things, but this is the best my amateur brain could come up with.

However this wouldn't work for my turntable as the input signal is analog.. sigh. hrm.. there must be a good way of doing this without sacrificing any sound quality.

Any advice would be greatly appreciated thanks.

Maybe I just need new speakers with bigger woofers in them and sell these infinities and the sub. (I can fetch about $300 for them all).. However, the sound of these infinities is hard to beat.

Help! thanks lol.
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Old 14th March 2012, 05:42 AM   #2
diyAudio Member
Join Date: Jul 2003
Location: Dona paula, Goa
You need a subwoofer filter, which basically is a low-pas filter. However these take the analog L/R signal as the input.

Gajanan Phadte
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Old 14th March 2012, 05:59 AM   #3
diyAudio Member
Join Date: Oct 2011
Originally Posted by gmphadte View Post
You need a subwoofer filter, which basically is a low-pas filter. However these take the analog L/R signal as the input.

Gajanan Phadte
The subwoofer has a built in low pass filter and adjustable with a knob, along with a knob for the gain. It's a powered sub with its own amp.

Btw, the sub also has a pair of speaker level ins and outs.. I wonder if I use these instead of the rca inputs, if it would sound better.
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Old 15th March 2012, 04:59 AM   #4
diyAudio Member
Join Date: Jul 2003
Location: Dona paula, Goa
Use two buffers in each channel and then add the signal using two resistors of about 2k2.
Pedja Rogic buffer sounds very good, but should select good filter for its supply.

Gajanan Phadte
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Old 16th March 2012, 12:06 AM   #5
dangus is offline dangus  Canada
diyAudio Member
Join Date: May 2004
Location: Vancouver Island
A standalone Dolby Digital decoder/processor should act as an active crossover and DAC for PCM signals. Now that HDMI has made them obsolete, you should be able to pick one up fairly cheaply. Just make sure it does "bass management" for PCM; occasionally that feature is overlooked. There were a bunch of these made back around the dawn of DVD when AV receivers were sold as "digital ready" with analog 5.1 inputs.

The Technics SH-AC500D was popular because it was the only affordable unit with DTS and it included remote volume control so it could be connected directly to separate amps; under $100 on eBay.

Some AV receivers have preamp outs. Non-HDMI receivers are obsolete, and can be picked up in thrift stores for as little as $20.
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