Can I Use My Amp's Speaker B Jacks for My Sub?

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A I’m using a Yamaha AX-497 integrated amplifier to power a pair of Elac speakers with a nominal 4-ohm impedance. I also have a Yamaha YST-SW315 subwoofer I’d like to use in my system. Here’s my question: If the speakers are wired directly to the amp as speaker pair A, and the powered subwoofer is connected as speaker pair B, can I power both simultaneously without damaging the amplifier? (The amplifier’s manual warns against connecting more than one pair of 4-ohm speakers.) For convenience reasons, I would rather not wire the main speakers through the subwoofer. —V.A. Dare / via e-mail

Q When you use a receiver’s or integrated amplifier’s Speaker A/B switch to send signals to more than one passive speaker pair, you effectively double the load (by reducing the total impedance) on the amplifier. This creates the potential for overload and overheating, especially in situations where more than one low-impedance speaker pair is connected. That’s why Yamaha warns against it in your amp’s manual. The subwoofer you’re using is a powered model, however, so it will add virtually no extra load to your Yamaha AX-497 amp.

The main rationale behind wiring your main speakers through the speaker-level connections on a subwoofer would be to utilize the sub’s often included, but rudimentary, built-in passive crossover. This serves to filter out low-frequency information to remove some of the burden from your main speakers. However, the YST-SW315 subwoofer’s manual doesn’t mention a speaker-level filter. What the sub does provide is a control called High Cut—basically, a low-pass filter—that Yamaha recommends you adjust to match its upper range to the natural roll-off of the lower range of your main speakers.

Some stereo receivers provide line-level preamp outputs in addition to their speaker-level outputs. If your amp provided this feature, it would generally be recommended to run a pair of interconnects to the Yamaha sub’s RCA line-level inputs. But since your amp lacks preamp outputs, your only options are to wire your Elac speakers through the speaker input/output terminals on the back of the Yamaha sub, or, as you suggest, use both the A and B speaker outputs of your integrated amp simultaneously. In this situation, it won’t matter which of those two connection schemes you pursue. What will be important is to set the sub’s High Cut control to achieve the best possible blend with the main speakers.

pw's picture

ATI sells a 4 channel power amp, would this work well??