Can I Bi-Amp the Definitive Technology BP9040 Speaker? Ask the Editors

definitive technology bp9040

Note: I had originally misinterpreted Esteban’s question, which I’ve now cleared up with him. So, I’ve updated this article to reflect his real question.

Q: I just got a pair of Definitive Technology BP9040 speakers, and I absolutely love them! Can they be bi-amped? I currently have them configured as “small” speakers in my Marantz SR5012 AV receiver, and the integrated, powered subwoofers in the speakers are connected to the LFE outputs of the AVR. If I set two spare surround channels in the AVR as front channels, can I connect both outputs (front and surround-assigned-to-front) to the speaker’s main input? Would that make sense?

– Esteban Cruz (IndieHappy)

A: No, I’m afraid that would make no sense whatsoever. Never connect more than one amplifier output to one speaker input! You could easily damage the speaker. What you propose is the function of a mixer, which uses electronic circuits to combine two or more signals together safely. And even if you were to use an external mixer to combine the signals from the front and surround-assigned-to-front channels, those signals are identical, so you would simply get the front-channel signal. The result would have nothing to do with bi-amping.

To bi-amp a speaker, it must have separate inputs for the woofer and midrange/tweeter. These inputs are fed by separate amplifiers, which could be outboard units or two channels of a multichannel amplifier or AV receiver.

In some cases, a crossover circuit is inserted between the source and the two amps. Some AVRs include such a crossover for bi-amping using two of their amp channels, or it could be an outboard unit inserted between the source and two external amps. This crossover separates the low frequencies from the mids and highs, sending the lows to the amp driving the woofer and the mids and highs to the amp driving the midrange and tweeter. In other cases, both amps can send the same full-range signal to the speaker’s woofer and mid/tweeter inputs, and the crossover in the speaker separates the frequencies accordingly.

Does bi-amping improve the sound quality of a compatible speaker? That’s the subject of endless debate, which I’ll leave to others in the comments.

None of this is possible with the Definitive Technology BP9040, because it does not provide separate inputs for the woofers and mids/tweeters of the main speaker. Of course, it does provide a separate input for the built-in subwoofer, but this is not the same as bi-amping. Because the sub includes its own amplifier, that input is a line-level connection designed to be connected to a line-level LFE output from an AVR. By contrast, bi-amping works with speaker-level signals from outboard amps.

Fortunately, the Marantz SR5012 AVR provides two sub outputs, so all you need to do is connect them to those inputs on the speakers. You are correct to configure the main speakers as “small” in the AVR if you’re going to use those subs. DefTech recommends setting the AVR’s crossover to 80 Hz, which is the normal default setting.

For those with an AVR that provides only one sub output, a simple, inexpensive “Y” cable will split the signal so it can be sent to both subs. This is the opposite of mixing two signals together, and it’s perfectly safe. Of course, you also need to connect the speakers’ power cables to an AC outlet, since the subs’ amplifiers must be powered in order to function.

As a side note, the BP9040 includes some rear-firing drivers, so I hope you have them positioned somewhat away from the back wall. Placing them up against the wall will compromise the sound from those rear-firing drivers. Also, don’t place them too close to the side walls, since the subwoofer fires to one side, and the passive radiators fire to both sides.

FYI, here’s another Ask the Editors about using a separate subwoofer with the Definitive Technology BP9040 speakers.

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