Subwoofers not only add depth and drama to your audio system, they also reduce the demands on your main speakers, allowing smaller speakers to fill big rooms. Subwoofers can be standalone components or part of a home theater system, so the unit you select may dictate how you connect the sub to your system. Older stereo systems may not have dedicated subwoofer support, but contemporary subs can still be used.
Using Dedicated Outputs
Locate the subwoofer preamplifier output. Many surround-sound home theaters and stereo receivers have an output designed for use with a powered subwoofer -- usually one or two RCA-style jacks labeled "Sub," "Pre-Out," "Subwoofer," "SW Out," "LFE" or some combination of these.
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Connect a coaxial cable with RCA-style plugs to the subwoofer output on your receiver. These cables are often supplied with the subwoofer. Route this cable to the low-frequency effect jack on the powered subwoofer. This jack is labeled "Line In," "Low Level In," "LFE In" or something similar. There may be other jacks on the subwoofer, but those are unnecessary for this connection type.
Connect the subwoofer's power cable to a wall outlet and switch the unit on. Powered subwoofers contain an amplifier dedicated to driving the subwoofer speaker. The subwoofer preamp output provides a low-level signal for the sub's amplifier, and it is not powerful enough to drive speakers on its own.
Receivers With No Subwoofer Output
Locate the subwoofer's regular audio inputs to use with receivers that have no dedicated subwoofer support. The subwoofer accepts the signal from your receiver's speaker output in this configuration.
Connect the left and right audio inputs on the subwoofer to the left and right speaker outputs on the receiver. The subwoofer usually has RCA-style connectors for this configuration, while your receiver may use bare wire or binding post connections. Add the subwoofer left and right connections to the existing speaker connections, leaving your regular speakers connected as well.
Connect the subwoofer's power cable and switch the unit on. Since the sub is receiving the same audio content as your regular speakers, use the subwoofer's crossover control to customize low-frequency response. If your sub has only a volume control, the crossover is internal and low-frequency content is controlled by subwoofer volume only.
You can use the adjustable crossover control to match your subs to your main speakers. Set the crossover to 100 hertz or higher, if the largest speakers in your main speakers are 4 inches or smaller. Main speakers with woofers 5 inches or larger work best with the sub's crossover set at 80 hertz or below.
The amplifiers in your receiver are designed to work with speakers of particular impedance ranges, expressed in ohms. While connecting a subwoofer will have minimal effect on the impedance, don't be tempted to add further speakers to your receiver to the same inputs without calculating the resulting impedance load, or you could damage your receiver.