06-21-2006, 03:36 PM
Join Date: Aug 2003
Location: Burke, VA
My Ride: 2003 330i
| I have never thought about approaching it that way. Pretty ingenious way of doing it without specialized equipment. Just wanted to make a couple comments to benefit people that don't have much experience with this.
Most multimeters are designed to measure voltage at 60Hz (house AC US-standard frequency), so a 60Hz, even a 50Hz tone should give you an accurate RMS reading (i.e. good for setting up an amp for subs), but if you try the same procedure for upper range (I normally use a 1,000 Hz tone), then, depending on the meter, your voltage reading might not be very accurate (especially with a cheap meter).
Another thing to point out is the fact that a no-load voltage reading, could be different than a voltage reading with speakers connected to the amp. Unfortunately, a sine wave can damage a speaker, so it is best to do it without a speaker connected to the amp, and you have to be very careful if you try to do this with a speaker. Sometimes I use an old subwoofer as a dummy load to setup gains for front/rear speakers.
Using common sense is also very important. For example, if the head unit is rated at 3-volts output on the RCAs, and the amplifier dial on the gain reads (for argument's sake) 1 volt at a minimum and 5 volts max, then you expect a properly adjusted gain to be at the middle (around the 3-volts mark). If it isn't then you can suspect something is not right.
As suggested above, it is very good practice to get a bigger amplifier than what you need. An amplifier that is not being pushed to its limits will perform better, will not heat up as much and last longer. Kind of like having a big engine in a car. You will not be going full-speed all the time, but it does take less effort to accelerate and it is not being stressed as much during normal driving.
There are other ways to setup amplifiers. The best way to do it is with test tones and an oscilloscope, but as stated above, most people don't own test equipment. Most shops don't own scopes either, they just set gains based on experience/by ear on their garden variety installs.
Another way of setting up gains is using your ears as a tool. I would highly recommend getting a copy of the Autosound 2000 amplifier setting CD. It is cheap and can be used with either test equipment or for ear-tuning. The disk will help "train" your ears to learn what distortion sounds like.
For more details on system setting/tweaking, check out an article I wrote a while ago in my website: http://home.comcast.net/~customcarstereo/tweak.html