Hi, in need of advice. I just bought a center channel (infinity) and another Behringer A500 amp (2 channel) - i now have 3. I'd like to bi-amp connect it. Meaning one set of plugs on the center to channel 1, the other set of plugs to channel 2. I am using the balanced XLR connections to connect the speakers to the Outlaw990. The problem is that there is only one XLR connector for the center channel on the 990 and two XLR inputs into the amp. Any ideas?

I know i can bi-wire the center into the bridged amp and only use channel 1, connecting that to the outlaw's single XLR, but I believe that biamp'ing is better.

THanks much if anyone has any advice?
James

You can split the XLR output of the 990 with an external splitter to connect the center channel output to both channels of the amp, but I wonder what you'll gain over just bridging the amp to mono. You have the same amount of power going to the same speaker, and since you aren't doing active biamping (the speaker's internal crossover is still the point of crossover) you don't have the potential benefits afforded by biamping in that manner.

gonk's got it right. I'm not familiar with the 500, but my EP2500 has a DIP switch setting that will allow the single input to drive both channels of the amp.

Run the Behringer amp in BRIDGE mode, using the one cable from the Outlaw preamp. Connect one driver to the left channel output of the amp (from black to red NOT red to red as you would normally do with a bridge amp). Then connect the other driver to the right channel in inverted polarity i.e. with the driver's "red" terminal to the amp's black terminal and the driver's "black" terminal to the amplifier's red terminal.

All that setting a stereo amplifier to "bridge" mode does is to send the audio to one channel (usually the left) unaltered, and an inverted version of the same audio to the other channel. Usually in bridge mode the output is then taken from "red" terminal to "red" terminal. That is not what we are doing here; we are connecting it like normally, but with one channel reversed in polarity to make up for the polarity inversion done by bridging.

Trust me on this one......

Thanks for the replies. Looks like 2 different suggestions. Yes, the Behringer A500 has the bridge/stereo DIP switch. So if i get this right, Gonk and Otto suggest, bridging the amp and running all four speaker wires (bi-wire) to the bridge (the middle red and red). In the A500 this would be channel 1 and you would put channel 2 volume off. I looked at the EP2500 manual and I don't see how a mono input can drive both channels (ie in stereo).

Altec, your suggestion is also to bridge. But hook first pair from the center to channel 1 (normal polarity), and second driver to channel 2 (in reversed polarity). I'm assuming you would then keep both channel 1 and channel 2 volume controls turned up, correct?

Thanks much for the replies, finding the various options a bit confusing. Will try both ways and see how it sounds, the reversed polariy kinda scares me a bit, but Altec sounds very convincing :-)

This weekend, hook up center and 990 firmware update, fun fun :-)

just found in the EP2500 manual the run in parallel option, one input, both channel output. unfortunetly the A500 does not have a DIP switch for that. Just the stereo/bridge one.

Thanks again, and any other comments on set up would be very much appreciated.

- James

Hi there,

I guess you could try it a couple different ways. If you want to bi-amp, then that precludes the bridging method. The bridge method, by definition, is only a single channel, and then you are no longer bi-amping, but rather bi-wiring.

If you really want to bi-amp, and your A500 doesn't have the run in parallel option (sounds like it doesn't), then you will have to split the output of the 990 and feed both inputs of the A500. Each output of the A500 is then isolated from the other, and you will be passively bi-amping. Of course, you will remove the jumpers on the speaker wire inputs of the speakers themselves.

I see what Altec is saying, but I've never tried it. I see that he's making an assumption about while channel maintains uninverted polarity ("usually the left"), so it's possible that you will run into polarity problems with respect to your other speakers. In general, I see how this implementation could work, but I wouldn't personally do it without understanding exactly what's going on. You could figure it out empirically if you have an oscilloscope.

If you're worried that you're underpowering your center, I think you'll get the quickest and easiest mileage out of simply briding the amp and single-wiring the speakers.

There is a slight electrical advantage from passive-biamping. However, I really doubt how audible it is. I'd say that some people might be able to hear it in fine musical recordings. While the center channel is an extremely important component for home theater, I think its fidelity is reliant upon much more basic things that separating the high pass and low pass internal crossovers. If you find your amp is running out of gas power-wise when driving the center, using bridge mode will generally get you the same amount of power as bi-amping.

Bottom line: 1) bridge the amp and single-wire for maximum power to the speaker; 2) split the input from 990 to A500 and run each channel independently if you want to passively bi-wire (see if you can hear a difference in blind testing!) and 3) do the bridge mode with one channel inverted if you want to do the bi-wire thing with a twist.

Good luck!

It's not an assumption on my part, but it is the way amps work in bridged mode. In "bridging" the ONLY thing that is going on is that the same signal is sent to the two channels, one being inverted. When connecting to the two "red" terminals, the voltage difference between them is double because of the polarity inversion, thus 4 times the power output (in a perfect amp).

The regular single ended signal is still available on the two outputs of the amp on the "red" and "black" terminals, at the normal power levels for the amp, and there is no reason you can't use them instead of taking the signal from the two red terminals.

Doing this is just a simple way to get the same mono signal to go to the two channels. The only thing that has to be done is to reverse the speaker leads on the channel which has been inverted in polarity.

Yeah, I see what you're saying. But the assumption part is that the left channel is non-inverted and the right channel is inverted, thus your direction to invert the right channel. You're right in that they are now in correct phase with each other.

The distinction I'm making is that there's no technical reason that the left channel must be the non-inverted one. If we don't know which one is inverted, it's possible that the center channel signal will become out of phase with respect to the rest of the system.

I suppose that there's also a potential to get out of phase if using different amps as well -- if you're using one inverting amp and another that's non-inverting. The best way to assure proper polarity in this "mixed" case is to measure it.

thanks guys, will try both ways. the manual says when bridged to use channel 1 (and turn the gain on channel 2 off). So assuming its channel 2 (the right) is the inverted one where i need to switch the black to red and red to black. I guess since the bridge switch is on, that I'll continue to keep the channel 2 gain(volumn) all the way off, correct? will reply back if i can tell any difference between the two options.

- james

It's usually the left channel which is non-inverted and the right channel which is usually inverted, at least in amps I've designed or been in on the design process. But in the end, it depends on the particular amp for which is which.

At any rate, the channel which is non-inverted is the one which accepts the input. If that's the left channel, then that channel is non-inverted. If it's the right channel which accepts the input, then the right channel is the one which is non-inverted.

I looked at the manual a day ago, and (keeping in mind too little sleep since then) I think it was the left channel that took the input for bridged mode...

Yep sure is, channel 1 is the left so in bridged mode that should be the non-verted one.

Otto, quick question for you (off topic), i was looking at the EP2500 as well. Decided against it because of the potential of fan noise. Do you notice the fan noise from the amp in your HT setup? If so how bad is it? Much thanks for the replies and looking forward to setting it up tomorrow when i have the time.

- James