Tune car audio
You have finally hooked up all your sources, processors, amplifiers and speakers. Now it is time for one of the most critical aspects of the installation: Fine tuning your system (tweaking). Tweaking is a very long process, especially if you have many channels of amplification. Take your time to get everything set for optimum performance. Professionals take days, even weeks to set a system up.
1. Get rid of noise
Make sure your system is 100 percent noise free (see the "alternator noise" section for more help).
2. Check speaker polarity
To make sure all your speakers are in phase, unhook the speaker you want to test at the amp (both wires preferably). Using a 1.5 volt battery (any size), touch the positive terminal of the battery to the positive wire going to the speaker, then do the same for the negative wire. Have a friend look at the speaker. If the speaker pops out, the polarity is correct. If the speaker pops in, the speaker is hooked up backwards (out of phase). To fix this, simply reverse the wires when hooking the speaker back to the amplifier. A word of caution here: DO NOT hold the battery power to the speaker for more than 1 second, all you want to do is to see if it pops in or out. You will damage the speaker if you hold constant power to it. Do not use a higher voltage. Also, do not try this test on tweeters, you could fry the voice coils. If there are crossovers with capacitors along the line, this test will not work (capacitors block DC voltage). Bypass the caps momentarily.
A much more elegant and quicker way to do this is by using a commercially available polarity checker, which uses a test CD. All you have to do is pop the CD in the head unit and hold the polarity tester in front of each speaker. The advantage here is that you can test for absolute polarity of the system on all the speakers, including tweeters. Polarity checkers are available from various companies such as Monster Cable. Retail for the Monster Cable polarity checker is about $120.
Sometimes, when speakers are not mounted close to each other (i.e., mids on the doors and tweeters up in the dash), reversing the polarity on tweeters or mids makes the system sound better because it makes up for phase differences due to distance. Try different combinations and see what sounds better.
3. Get a clean signal
The third step is to set all your sources and processors "flat". Turn the loudness off. Set the bass, mid and treble controls on the radio to 0. Set all EQ bands to 0dB. Defeat all bass and treble boosts, etc. Set the gains on all the amps and processors to the middle. Balance and fader should also be in the middle. By now your stereo should sound pretty good. If not, check your installation. EQs are not designed to compensate for installation flaws.
4. Setting Gains for max. power and min. distortion
Start with a high level signal at the first components of the chain. This will reduce noise and give you more headroom. Try to start with a head unit that has a high voltage signal. With everything still flat, set the amplifier and processor gains. Pegging the gains on amplifiers or any other processor all the way up will most likely introduce clipping (distortion) in your system, which damages speakers.
The best and quickest way to set gains is to use an oscilloscope. By using a scope, you will be able to get the maximum possible power without distortion. Make a probe adapter using a male and female RCA ends (see figure). Splice a wire in the positive (center) and one in the negative (outside). Insulate exposed wires independently. To probe a channel, simply unplug the RCA from the component, plug the RCA to one end of the "probe" and plug the probe to the component. Hook up the scope's probe to the two wires you spliced.
Once you probe is hooked up, you need to pop a test CD with different test tones such as the Autosound 2000 amplifier setting CD. Make sure the tones are at 0dB reference. Use a frequency in the middle range of the crossover. For example if there is a crossover before the amplifier that lets frequencies from 100 to 3000 Hz pass, use a 1000 Hz test signal. For subs try about 40Hz.