Subwoofer Connection Question

[PeterR]

I just ordered a subwoofer (Dayton Audio SUB-800) as part of my first entry int the mid-fi/hi-fi experience. The receiver I'm using (Onkyo TX-8255) doesn't have a sub out connection, so I have a question about connecting it.

I'm going to have to use the speaker level inputs on the sub, but I don't want to use the speaker outs because my speaker wires are already run through the walls and it would be difficult to pull them out and re-run them from the other direction (the sub will be placed far across from where I now have the receiver). So, what I want to do is leave the speakers connected as Speaker A and connect the sub as Speaker B; then, I'll just leave both Speaker A and B selected at the same time.

My question is this: by using this method, am I downgrading the sound quality or the effectiveness of the subwoofer in any major way? Is it much better to connect the receiver to the sub's speaker level inputs and then run the speaker wires from the speaker level outputs?

Any suggestions/advice would be much appreciated. Thanks.

[John K.]

Peter, the A and B terminals on the 8255 are simply an internal "Y" arrangement connecting them in parallel to the output channels. The two terminals therefore have exactly the same content, and the sub will receive the same voltages it would if it was connected to the A terminals. The alternate connection you describe, running the speaker wiring from the sub's speaker level outputs after wiring the A terminals to the sub inputs is electrically the same thing(the "Y" split then occurs inside the sub), and could be used if more convenient(e.g., shorter connections).

[PeterR]

Thanks for the response. I'm kind of new at this, so I hope this isn't a stupid question, but are you saying it doesn't really make a difference which way I do it, or is one definitely better than the other?

[rooftop59]

No you will not degrade the sound quality. you will be running a true two setup where you let the monitors play their full range and then blend the sub in. I would begin with the speakers lower -3 db point (probably around 65 Hz) and start by setting the sub crossover there. the advantage of using the speaker level inputs and outputs is that you would be able to set the crossover higher and take some of the bass away from those little bookies. this would allow them to play louder with less distortion. but the method u describe should work.

[PeterR]

Thanks again--that should work fine, because I never really play the music too loud anyway. It's more of a casual listening setup, but the Polks are lacking a little bit of bass presence by themselves. Sounds like this could fill in the bass just the way I need.

[PeterR]

One more question--if I'm connecting the sub to the Speaker B outs, do I need to connect both the right and left channels? I read somewhere that subs were a mono signal, but I might not be understanding that correctly.

[rooftop59]

The sub is mono, but it will sum the right and left inputs, so the answer is yes, connect both left and right. Otherwise you will only get the bass content from one channel, which would sound a little strange.

[PeterR]

Ah, okay...I think I get it now. Thanks for the help. The sub should be delivered tomorrow and I can't wait to hook it up.

[John K.]

That's right, Peter; it doesn't really make a difference which connection method you use. As was said, if you use the A and B terminals the split of the wires to the speakers and sub takes place inside the receiver. If you wire A into the sub the split of wires takes place inside the sub. This makes no significant electrical difference. Note that even if you wire the speakers through the sub, they get a straight-through feed from the receiver, just as if they were connected directly to the receiver terminals. There is no "crossover" inside the sub, even though the control is (mis)labeled as such. This is just a low-pass filter which rolls the sub off above the selected frequency, but has no effect on the connected speakers, which continue to get the full-range signal, including the low bass.

You'll adjust the so-called "crossover" control to try to get a smooth blend with your speakers. These controls generally aren't particularly accurate as far as the numbers on the dial go, and something a little below the mid-way point probably will result in reinforcing the 40-80Hz bass range for your speakers.

As to mono/stereo in subs, there's little or no "stereo" content in recordings below the 100Hz or so which subs generally cover, and any difference which would be there in the left and right channels below about 100Hz would be combined to mono inside the sub anyway. Nevertheless, to assure that nothing is missed, you should connect both the left and right channels into the sub. Enjoy.