Using a Subwoofer in a System with no Subwoofer Output
With so many people using home theater systems, we're used to seeing preamps and processors that have a subwoofer out; often called the 0.1 channel or LFE output. But we're not looking to discuss subwoofers in a multi-channel setup here... we're more interested in two-channel with this tutorial. In a regular stereo amp that has no surround processing, if you see something marked "subwoofer out," it's typically another preamp output. In essence, nothing more than voltage signal coming from the preamp, fed to the woofer's amplifier.
So what happens if you don’t have a preamp out?
Most subwoofers are designed to handle this situation. They have a high-level input (sometimes called speaker-level input) that hooks up to the speaker taps of your amp. All you do is run another pair of speaker cable from the output taps of your amplifier into the high-level input on your subwoofer. This connection works the same way as a preamp/subwoofer output: It takes the voltage from the amp as the signal and sends it into the subwoofer.
This does not cause a power draw on the amp you hook up to. It is merely sharing the signal with your main speakers, not the power of the amp. This means there is no power draw, and the impedances all remain the same.
In fact, even if your preamp or integrated has a preamp/subwoofer output, you may want to consider using the high-level connection method. The most prestigious subwoofers in the industry are made by REL of England. They are the “Gold Standard” of the industry and priced accordingly, topping out at $9,000! REL recommends using the high-level input for all of their subwoofers. The reason they recommend this type of connection is as simple as it is logical: it ensures your subwoofer is seeing the EXACT SAME SIGNAL as your speakers. If you use the preamp/subwoofer output from your preamp or integrated, the signal seen by your subwoofer does not include the tonal balance and timing cues created by the amp. By using the high-level connection, the subwoofer gets the same signal as your main speakers, keeping them in better synch with each other, thus improving sound quality.
One snippet of information: Often times subwoofers will allow you to hook them up to the speaker taps of the amp and to cross-over the main speakers, restricting how much low information they get. Don’t assume this is a benefit. It may allow the mains to play louder as they are not having to move as much air, but the downside is you can lose some clarity. Experiment as different products work different ways.