How to Wire a Sub Into a Factory Stereo
By David Lipscomb
Subwoofers are routinely added to stock systems to add much needed depth and impact. Subwoofers require amplification, since a stock radio cannot power these devices on their own. Using the right adapter and choosing the best subwoofer and amplifier combination, you can get the factory stereo sounding its best within an afternoon using basic wiring skills.
The vast majority of stock radios do not include outputs on the back for wiring amplifiers. These RCA connections known as preouts provide a clean line-level signal for new amps added to the system. However, line out converters colloquially known as "LOCs" solve this issue, wiring into the speaker level leads on the back of stock radios and converting the signal to a low level. From there, RCAs carry the signal to the subwoofer amplifier. No other factory wiring need be interfaced other than the accessory wire on the stock radio, used to activate the new amplifier when the stereo is turned on.
Impedance may be the single most important measurement when adding subwoofers to any amplifier. Impedance measures the amount of effort the amplifier must exert to push a speaker or subwoofer, with lower impedance numbers indicating more work is required. The lower the impedance, the higher the wattage output, but this has its limits. Running subwoofers below 2 Ohms is normally dangerous to amplifiers, risking overheating, consistent activation of protection circuitry or damage. The "sweet spot" for driving subwoofers is between 2 and 6 Ohms. Read your amplifier's documentation carefully to see what power ratings are offered at what impedance. Avoid running subwoofers at any impedance the manual does not list.
SVC or DVC?
Single and dual voice coil subwoofers can offer similar performance results, with dual voice coil models providing enhanced wiring flexibility as your system expands. DVC subwoofers come in dual 2-, 4- or 8-Ohm varieties, which may be wired for a lower or higher impedance as system demands dictate. For example, a dual 4-Ohm subwoofer can be wired to 2-, 4- or 8-Ohms. A single 4-Ohm coil subwoofer is driven at 4-Ohms at all times. This is accomplished by jumping voice coils in specific patterns, while the amplifier is always wired using the positive and negative speaker output leads. If you're bridging an amp, you only use the left positive and right negative leads.
Understanding Power Ratings
Power ratings on an amplifier or subwoofer are contingent upon a few factors. If an amplifier is rated at "1000 watts," rarely does that mean that is full time power, nor should it imply that the amp can run that high for more than a few minutes continuously. Amplifier power output is a function of speaker impedance, not the power handling capability of the subwoofer. For example, if you purchase a 1000 watt subwoofer and drive it with a 100 watt amplifier, the amp will not magically produce 1000 watts. Using a mono amplifier rated at 200 watts at 4 Ohms usually yields output at 400 watts or more driven at 2 Ohms. Use RMS or average power rating on the amplifier and subwoofer to create an ideal match.
Regardless of which speaker you choose, they sound better after a few hundred hours of play, during which the speaker's suspension becomes more compliant. During this initial break-in period, drive subwoofers of any flavor modestly while the suspension remains stiff. Although some subwoofers benefit more from this than others, a looser suspension requires less input power to get the speaker to move further.
David Lipscomb is a professional writer and public relations practitioner. Lipscomb brings more than a decade of experience in the consumer electronics and advertising industries. Lipscomb holds a degree in public relations from Webster University.