Subwoofer to PC (single RCA to ctr/sub 3.5mm port)

vhakki

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Sep 1, 2014
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Hi,

I bought Yamaha YST-SW012 subwoofer as my PC subwoofer since my 2.0 speakers cant really play low frequency at all. I searched how to connect it to motherboard but all the articles' subwoofers had 2x RCA inputs and Yamaha YST-SW012 has only one RCA input. What kind of cable/adapter should I buy to plug it into my mobo's 3.5mm output? The motherboard has built-in audio amplifier and port for center/sub speaker.

Back of the subwoofer:
http://
 

nukemaster

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Subs are a single channel, thus why you only have one.

Here comes the interesting part.

Most systems that use a sub are 5.1/7.1 channel. In these systems the computer can strip out the low frequencies from the music and send them to the sub output(that happens to be with the Center channel because computers use 3.5mm stereo jacks).

Now if that sub has a built in crossover, you can actually just remap one of the other plugs to do front left and right and combine them.

To do it the right way, you should place resistors in from of each channel to "sum" them into a single channel for the sub. Passive summing will cost you volume, so the sub will need to be turned up louder to keep with the speakers(you should only have to make this adjustment once).

You can find more information on combining channels here.
http://www.all-electric.com/schematic/simp_mix.htm Bottom of the page first one with the 4.7k resistors
And a more for your situation here. You want the Stereo-to-Mono Summing Box. 475ohm resistors are much less costly to overall volume as well.
http://www.rane.com/note109.html

Now this all relies on the sub having a crossover because you do not want the sub trying to play mid range sounds. The specs list 28-200 Hz so I would guess that is the crossover in the sub. If you wanted it to only play upto say 80-100, you would want to build a low pass filter.
 

nukemaster

Distinguished
Moderator
Subs are a single channel, thus why you only have one.

Here comes the interesting part.

Most systems that use a sub are 5.1/7.1 channel. In these systems the computer can strip out the low frequencies from the music and send them to the sub output(that happens to be with the Center channel because computers use 3.5mm stereo jacks).

Now if that sub has a built in crossover, you can actually just remap one of the other plugs to do front left and right and combine them.

To do it the right way, you should place resistors in from of each channel to "sum" them into a single channel for the sub. Passive summing will cost you volume, so the sub will need to be turned up louder to keep with the speakers(you should only have to make this adjustment once).

You can find more information on combining channels here.
http://www.all-electric.com/schematic/simp_mix.htm Bottom of the page first one with the 4.7k resistors
And a more for your situation here. You want the Stereo-to-Mono Summing Box. 475ohm resistors are much less costly to overall volume as well.
http://www.rane.com/note109.html

Now this all relies on the sub having a crossover because you do not want the sub trying to play mid range sounds. The specs list 28-200 Hz so I would guess that is the crossover in the sub. If you wanted it to only play upto say 80-100, you would want to build a low pass filter.
 
You need a cable that has a stereo mini plug (not mono) at one end and 2 RCA plugs on the other end. One plug is for the sub, the other for the center channel (which you do not use). Change your audio control in the PC so it knows you have a 2.1 system. Depending on the audio driver for the mobo you may adjustment for how high the sub plays and how loud. You want it to balance its' level with the speakers so that the bass is not muddying the midrange.
No summing required.
 

nukemaster

Distinguished
Moderator
I have never seen a 2.1 option on computer only stereo(Realtek, ITE, and Creative all seem to lack a 2.1 option). Can you please add more information as this would be useful to MANY users here.

I do know at one point HP used to have adapters with its systems for a sub. These systems had an amplifier onboard so needed passive speakers and an active sub.

You are 100% right about not having the center being mixed in with that mono cable(on top of having the center and sub channel fight it out.).
 
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