Amplifier power, the number of car audio subwoofers and subwoofer impedance dictate how you wire everything up. Variables such as whether the subwoofer is single or dual voice coil must be considered because the wrong wiring scheme results in diminished output or amplifier instability. Once you have a grasp of these electrical relationships, you can wire your subwoofer for the best possible sound and equipment longevity.
Impedance and Stability
Amplifier stability is the key consideration when wiring any subwoofer. Subwoofer impedance directly impacts this, since most cannot reliably handle excessively low loads. Most amplifiers are geared to operate between 4 and 8 ohms, with impedance fluctuating depending on frequency. At minimum, heat buildup from low impedance results in frequent shutdowns or the amplifier entering protection mode. If the amplifier cannot handle the load, device damage or excessive distortion may result. If that distortion becomes too high, subwoofer voice coils may heat up and damage the speaker. Conversely, if impedance is too high, acoustic output may drop to the point where bass and dynamics are lower than necessary, providing an unsatisfactory listening experience.
Single and Dual Voice Coil Speakers
A single voice coil subwoofer connects to its amplifier in a straightforward manner, with the positive terminals on the speaker and amplifier wiring directly together as well as the negative terminals. Dual voice coil subwoofers are where things get potentially tricky – 2-ohm voice coil speakers must be wired in series to raise the impedance to 4 ohms, since most amps cannot handle loads below 2 ohms. This is accomplished by connecting the outer set of binding post terminals to the amplifier, jumping the middle terminals together. Conversely, wiring a dual 4-ohm speaker to 2 ohms increases power output, wiring positive subwoofer terminals to positive and negative to negative. Review your amplifier's low impedance drive capabilities in the product literature, examining the impedance ratings for 1- and 2-ohm operation. Select your subwoofer accordingly, always attempting to stay within 2 to 4 ohms whenever possible.
Bridging an amplifier is the act of wiring the left positive and right negative terminals to the subwoofer, increasing the amplifier's output. Amplifiers rated at 150 watts per channel can output as much as 600 watts mono in this configuration. The same rules apply when observing total impedance of the subwoofer, although when bridging, it's always wise to connect a 4-ohm load to the amplifier to prevent thermal issues. Four-channel amplifiers may be bridged to a high-output, two-channel configuration as well, increasing your wiring options.
Alternative Wiring Configurations
Mono amplifiers offering a single channel are normally geared toward connection to a subwoofer. Most mono amplifiers run very cool and thrive at lower impedances. Stereo amplifiers offer a little more flexibility, especially when driving multiple subwoofers. For example, a stereo amplifier can drive four subwoofers comfortably by wiring two 4-ohm voice coils in parallel per channel, forming a 2-ohm stereo load. Four-channel amplifiers may be configured for up to eight subs, wiring in the same manner. Alternately, wiring a single 4-ohm voice coil per channel creates a very easy and stable load for the amplifier, regardless of the number of amplifier outputs. Use your imagination, following the rule of staying above 2 ohms in most cases and avoiding total system impedance above 4 ohms for maximum output.
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