Amplification

Proper amplification for subwoofers and all other speakers is critical. Outboard amplifiers should be matched as closely as possible to the speakers' ratings for power handling. That is to say if you have front speakers that are rated to handle 50 watts RMS, the amplifier driving them should produce 50 watts RMS or very close to it.

Subwoofers demand a great deal more power than satellite speakers. The 500/1 amp that powers the 10W7 woofer in my car is a very solid piece of work. The pictures I had seen before I installed mine did not do it justice. It provides 500 watts mono RMS, exactly what the 10W7 woofer is rated to handle. Additionally, it has a lot of controls built in and accepts the necessary heavy gauge wire without a need for an adapter or wiring terminal. The 500/1 runs very cool even under heavy load but is thirsty for current, so make sure that you properly calculate how much power your alternator can spare if you install one.

To run the front speakers in my car, there is an old Sony XM 4040 amplifier installed, running at 40 watts into two channels at 4 ohms. Earlier I mentioned the matter of speaker sensitivity, and here is where it becomes relevant. Lower amplification matches well with higher sensitivity, and higher power matches to lower sensitivity. A more powerful amplifier can drive a less sensitive speaker quite nicely and will reduce the amount of hiss and noise.

Adding other amplifiers: I Got the Power

When you add outboard amplification to a car, you should try to stay within a safe zone and not continuously draw more current than it can provide. Adding a second battery does not help provide more power to your amplifiers, the only benefit to this is that you can play the stereo longer with the motor off.

A quick and dirty method to check this is to multiply your alternator's rating (usually stamped on the side) by 40%, or .4. This yields a very rough estimate of the reserve power your electrical system can supply. If the sum total of the fuse ratings on the amplifiers does not exceed this, you should be fairly safe.

Using this math my alternator should generate about 45 amps of reserve power. My J/L Audio 500/1 has a fuse rating of 50 amps (!) and so handily exceeds the safe zone. This does not include the other 20 amps that my Sony amplifier is fused by. What happens as a result of this is a dimming of headlights at moderate volumes as the battery attempts to meet the demand. The battery is not charging during those dimming periods, so continuing to listen with dimming headlights should be avoided. I need to fix this problem, and the likely solution is to upgrade the alternator. That is another expense that I don't need right now, so I don't anticipate it happening soon.

Stiffening Capacitors

Capacitors, sometimes called stiffening capacitors, can help alleviate dimming headlights somewhat and are intended to provide instant amps from your electrical system as needed. Capacitors store electrical energy and release it instantly on demand, which can tighten up sub-bass. A well designed sub amplifier will produce controlled output regardless, but having the cap never hurts!

The general rule of thumb is to provide 1 farad per 1,000 watts of amplification. Capacitors must be installed correctly and need to be charged before use. If you install the wires backwards, the cap will - not may, but will - explode. Never connect a capacitor directly to a live power line or you will see a pretty shower of sparks and arc-weld your wires, and possibly your fingers and face. Connect the cap first, and then supply power from the battery.

Wiring and Cables

Power and Ground

With high-powered amps, it is necessary to provide enough current (amperage) to the amplifiers. A well designed power distribution system will prevent a lot of heartache. I strongly suggest using 1/0 or 4 AWG cable to provide power from the battery. The positive line should be fused no further than 18 inches from the battery terminal to prevent fires and other accidents. Gold connectors resist corrosion and will last for a long time, and are also highly recommended.

When running the ground wire, the wire gauge should be equal to the input. There is as much current flowing through the ground wire as there is through the positive terminals. Using smaller wire gauges for ground purposes will cause the wire to overheat, resulting in the insulation melting and creating the potential for a fire. I should know, it happened to me once (sad sad sad). Wherever possible, ground wires should all terminate in the same location to prevent ground loops. Ground loops usually result in a clicking, mechanical sound that increases/decreases with vehicle speed. When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other.

Ground wires can be connected to a bare metal section of vehicle chassis. I have never run a ground wire back to the negative battery terminal, mainly because the cost of the thick cable is prohibitive and can be eliminated.

Signal Cables

RCA style connectors are the de facto standard on most aftermarket units. Buy and install a set of high quality, shielded RCA cables to transport the musical signal from the head unit to the amps. You will be glad that you did. Also, avoid running the signal cables near power lines if at all possible to reduce the possibility of intereference through induction. In other words, run your power cable down one side of the vehicle and your signal cables on the other side.

A final consideration: never, ever run cabling outside the vehicle chassis. This should be common sense but not doing this is just asking for problems. To boot, most cables are not designed to be exposed to exterior elements and the abuse of travel.

And there you have it, my recipe for good sound on the road. Hope it helped!

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