Car amplifiers offer a variety of wiring options, based largely on the number of channels in the amplifier and the impedance of the chosen subwoofer. Choosing the right amplifier with sufficient power to drive your 2-ohm subwoofer is key in determining how you wire them together. The goal of wiring a 2-ohm subwoofer to that amplifier is maximum sound output, while ensuring the amplifier remains stable enough not to shut down or enter protection mode.
Bridging an amplifier effectively reduces the amount of headroom available to the amplifier. Put simply, this means that the amplifier works much harder to produce more power, reducing the amount of power in reserve. Subwoofer impedance plays a role here, since the act of bridging an amplifier with a 2-ohm subwoofer means you have to select amplifiers rated for low impedance, sometimes in the 1-ohm range. These are not only rare, but often pricey and run hot. By comparison, mono amplifiers are often designed to run at 2 ohms, typically running cooler and operating at a higher efficiency than bridged stereo amplifiers.
Real World Power
Two-ohm amplifiers draw more current from an amplifier when compared to 4- or 8-ohm speakers. For this reason among others, this is why you should always carefully examine the actual power output of the amp, rated in RMS. Short for "root mean squared," RMS in application translates to the average amount of power provided by the amplifier when properly installed. Amplifier literature should document differences in output between impedances, with wattage ratings increasing as impedance drops. Note that stereo amplifiers will normally provide these ratings operating at different impedances in both stereo and bridged mono modes. Mono amplifiers only have one channel, so these ratings change with the subwoofer's impedance.
DVC and SVC
Dual and single voice coil subwoofers offer variables that must be considered when using 2-ohm subwoofers. Single voice coil subs wire in a straightforward manner, with the positive and negative terminals on the speaker wired to the corresponding terminals on the amp. Two-ohm mono or stereo loads are easily handled by most decent amplifiers. Dual voice coil subs that you can wire to a 2-ohm load at the amp are dual 4-ohm models, accomplished by wiring the outer positive and negative subwoofer terminals to the proper positive and negative terminals at the amp. The first and second positive terminals on the sub are daisy-chained together, as are the two negative terminals. Wiring a dual 2-ohm voice coil subwoofer to an amplifier in the same manner results in a potentially unstable 1-ohm impedance, or to a safe 4 ohms by jumping only the inner positive and negative terminals together on the sub. It's important to note that the final impedance at the amplifier dictates actual wattage output, not the power-handling rating of the subwoofer.
Wiring and Electrical Factors
Power and speaker wire are important factors when wiring any amplifier, regardless of the final operating impedance. In most cases, the prudent measure for wiring all but the smallest amplifiers is to use 4-gauge power and ground wire, fused at the battery and grounded within 18 inches of the amplifier. Lower gauges like 0 AWG are useful for power amplifiers operating in excess of 600 watts RMS, or if multiple amplifiers are wired together via distribution block. Speaker wires at low impedances should be at minimum 14 gauge, with 12 gauge ideal for any distance exceeding 15 feet between amp and sub. Remember that as you add amplification, the amperage draw may become a factor for your battery and alternator. Amplifiers operating at 2 ohms are probably drawing and producing more power, so you may want to look into these issues if you experience significant headlight dimming or less volume than anticipated.
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