Using stereo sound card to create a mono 2 way active crossover

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Not sure if this is the best forum for this question....and forgive me if it is a dumb one, but....
I figure that it should be possible to use my soundcard to create a two way mono crossover given the right app. After all it has two outputs. If I was able to put an identical (mono) signal into both L & R channels and then put a low pass on the L and a high pass on the R I'd have a 2 way active crossover. Yes, I know the quality may be suss....particularly with a cheap card, but it could be really useful for tuning up a single 2 way and working out the appropriate crossover freq and levels.

(actually the real reason I want to try this is that I already run an active 2 way set up, but my young daughter wants some sound set up in the garden for her birthday. It would be a real issue getting to my whole system and unplugging all my gear and moving it, but i figure that if I'd be able to just grab a single speaker box (they are heavy!), take it out the back, grab a cheap D class stereo amp I've got lying around, and drive this with a laptop with one channel for tweeter and the other for woofer, it would be much simpler. There is no crossover in the speaker)

I had a search but couldn't find anybody who had done this. I don't want to build a crossover, buy a mini DSP, etc. just for this simple gig. Any ideas?
 
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Download Jriver and try this: apply mono sound on source, then use the parametric EQ to enforce a XO independently on the output for left and right channels. A low shelf with very large negative gain is same as high pass. A high shelf with very large negative gain is low pass. My only question is whether or not PEQ can be applied independently for each channel. I believe so. You may need to resample your mp3's from stereo to mono first in different app so file is mono but plays indentical content through two channels. Then when using Jriver to PEQ each channel it should be good otherwise if applying mono in Jriver it will assume you want same EQ on both channels.

Neat cheap digital 2way active XO idea if it works. But only good for mono content.
 
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Wow...thanks for the lightning fast response xrk. I'll give it a go and report back. I can imagine that if this works it could be useful for others who wish to fool around with crossover slopes and points on a single box, without the investment in an active or DSP unit.
 
Just tried it and no probs with setting up separate low and high filters on L and R and playing through desktop speakers it is very obvious. . But as you suspected there is an issue when I select mono at the same time. Getting late here so i will dig deeper tomorrow.
 
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Kimbo,
Sounds promising! I would do it myself but don't actually have Jriver on my machine as my trial period expired long ago. I know you can use Audacity to apply a stereo to mono. In fact, Audacity probably has independent L/R PEQ you can apply to the mp3 file itself. Then anytime you play this mp3 in any player and hook L/R to tweeter/woofer of a speaker, you will have an automatic built-in XO! Also, Audacity is free (no trial period needed). Having a portable mp3 file that has built in XO for any player is kind of cool concept. Just wierd hooking up left and right from an amp to a bi-wired 2-way speaker :)
Good luck.

Edit: I just went into Audacity and there is actually a High Pass Filter and Low Pass Filter where you can select freq and slope. However, it applies to left and right. To get around this, make a copy of your song as two separate stereo tracks (4 total). On one track, pan hard left and apply the HPF, on the other track pan hard right and apply LPF. Then generate a new stereo combined track from these 4. You will now have a single stereo track with left as tweeter and right as woofer. Then convert final stereo track to new mp3 - done!

I just tested this concept and it works. Kind of creepy to listen to it with headphones - the tonal balance is correct but it throws your brain for a loop because your brain is doing the combining between the left and right ear - i.e. a two-way microphone :)

Attached is a test sound clip with a 350Hz -24dB/oct XO with Left as tweeter and Right as woofer. Enjoy!

:D
 

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So this sounds like a good tool for fooling around with crossover slopes etc. For example I currently have it set up with a crossover at 2000Hz and 24dB slope. So starting with a track that has already been made Mono and using this for speaker testing is a goer.

But for my issue of playing any of my daughters music in the garden I can't really go through all her collection and convert it all to Mono. I'll have a look at some other (free) media software and see if there is one that will perhaps perform the merge into mono before applying the filters so I can just leave her music collection intact.

Any suggestions aside from JRiver and Audacity?
 
That was spot on Nate. I ended up with in the Parametric EQ, in order from the top....

Add Left to Right (mode = Add (add source to destination)
Low pass at 2000 Hz (right) [24dB/octave]
High pass at 2000 Hz (Left) [24dB/octave]

I just played the Stereophile test CD (1) to check, as track two has a dog bark on left then right, and both played as Treble on left and Bass on right.
The funny thing is that a few seconds later the test track plays left and right out of phase, and the output was nearly zero. Ah ha, I realized that adding the antiphase signal will subtract from the original when mixed so of course I should have heard nothing.

Anyway, this is great and solves my problem.....at least until the 30 day JRiver free trail finishes. :)
 
You should be able to do any audio filtering and routing with a VST host program and the appropriate plugins.
That usually requires 2 sound cards although a virtual audio driver like JACK can be used in place of a physical sound card.
- In Windows select sound card 1 (or the virtual one) to be the default audio device. All applications should play through it.
- make a physical/virtual loopback(a patch wire) from the sound card output to it's input
- in a VST host program route the sound card 1 inputs through your desired setup going into the outputs of sound card 2. Connect your speakers to sound card 2.
One drawback is that the VST host has to always be running and the good ones cost money.
 
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