Car Audio 101

Division

A cheap digital multimeter (DMM) will run ~20 bucks and should be in any installers/DIY-ers toolbox already. You do NOT need an oscilloscope.

Here's a pretty easy tutorial anyone can follow on how to use a DMM to set their gains. The source is pretty reputable.

Clipping can be very difficult to hear, especially at lower frequencies. I'm a pretty big fan of math, and with some basic calculations, a volt meter, and a a 50hz test tone, you can properly, and more importantly accurately set your gains. Familiarize yourself with Ohms Law.

Why use a DMM to set your gains?
Accuracy, repeatability, and unlike your hearing, math doesn't change after years of excessive volume.

Here are some additional links to refer to when properly tuning a system:

Wattage - this puts ohms law in english.

Ohm's Law
Ohm's Law Calculators (is the most useful calculator)