Car audio systems offer a way to improve the aesthetic quality of your daily commute while putting a stamp of personalization on your vehicle. Like any set of electrical connections, you must observe certain guidelines ensure safety and reliability. In addition, you should make use of best practices proven to ensure top-flight sound quality to make sure your efforts pay the highest sonic dividends.
Wiring a vehicle takes time and isn't necessarily "fun." That doesn't mean shortcuts are acceptable, especially when you're dealing with high-amperage vehicle charging systems. Routing power wires from the battery through the vehicle firewall and away from foot traffic and abrasion is mandatory. Power wires carry current supplied by the vehicle's battery and although only 12 volts, they pack enough amperage to start a fire. For this reason, never route power wires the easy way though door jambs or under the vehicle up to amplifier mounting areas. Always cover power leads with wire loom, preferably routed through existing wire channels under the door sills where they remain protected. Power wires are selected based on the amperage of the system, ranging from thin 10 gauge for a single small amplifier to 0 gauge for a powerful multi-amp system pulling hundreds of amperes in current.
The ground is the other half of the system's electrical circuit. Grounds must always be bare metal and located away from weld points or seat belt bolts. These points indicate joins in the body or areas joined to the body, not a contiguous piece of the chassis, so electrical continuity is far lower at these locations. Additionally, all components should be grounded to the same point on the chassis except the head unit if necessary. This arrangement is best structured through use of a ground block, accepting multiple inputs and outputting a single ground wire to one point. The primary ground wire is always the same gauge as the primary power wire from the battery, and should always be as short as possible. Use a bolt and star washer for the tightest connection, and smear a layer of silicone caulk over the connection at the chassis to inhibit corrosion.
Protect Your System
Fuses protect power lines as well as system components. In the majority of cases, the fuses needed to protect each device are already installed in the components. The fuses you install deal with the power lines. Do not neglect this. The primary power lead from the battery is fused within 18 inches of the battery. Each power wire from each device is also fused through a distribution block. Using a fuse that is too large places the wiring and passengers at risk, since a dangerous short circuit will pass through the fuse as though it weren't there. Using a fuse that is too small is theoretically safe, but may continuously blow. Never replace a fuse that keeps blowing with a higher value, since frequent blow-outs are not only dangerous but also indicative of a fault somewhere on the line. Investigate the wiring for nicks, pinches and abrasions.
Preventing System Noise
One sure-fire way to inject noise into a stereo system is to route RCA signal wires right next to power leads. Since vehicles have two wire channels, one under each door, it's rarely necessary to route wires carrying the delicate musical information with power leads. Using a head unit with higher preamp voltage in the 4 to 8 range helps with noise rejection, by overpowering any interference picked up along the way with signal from the stereo. Additionally, this approach lets you to keep amplifier gains lower, maintaining higher dynamic range and placing less strain on your amps. Grounding all devices to the same chassis location is sound electrically and inhibits noise by keeping continuity the same across all components. Never disconnect RCA cables connected to a head unit with the vehicle on. This can cause small short circuits, blowing small fuses at the preamplifier output stage on the radio and creating engine whine.
Small components like active equalizers and crossovers draw 1 amp of current or less, but still require separate power, ground and remote leads. There's no compelling reason to route a completely separate wire from the battery all the way to the system common ground to do this. T-tap connectors are small plastic clamps with metal teeth that lock around the power and ground leads of the head unit or other unswitched 12-volt accessory wiring, providing instant juice. The other component of of the tap is a male spade, sliding into the clamp's receiving slot. Tapping into the head unit's power, ground and remote accessory leads provides power to these low-current devices in one convenient location.
Setting Amplifier Gains
The proper way to set gains is using a multimeter, adjusting the amplifier to the precise level that produces no distortion. However, there's an easier way to get you started. Play a CD or a music file on your portable player that you know provides strong dynamics and bass. Turn the amplifier gains all the way down, then turn the radio volume three-quarters of the way up. Gradually increase the gain until the music sounds slightly distorted, then back it down until the sound is clear again. This provides you with more space on the volume control to add a little more loudness as needed for quieter recordings without overloading the preamplifier inputs at the amplifier. Make sure to turn off all equalizer, bass boost and other processing on the head unit when doing this. Once you get the gain perfect, drop a bead of hot glue on the gain knob to keep it from moving from vibration. You can easily peel it off later if you need to make an adjustment.
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