That's better

After talking with the guy at Car Toys about the subwoofer, I discovered a couple of things:

• They generally turn the gain control on a subwoofer amp all the way up when they install it because most people want as much boom as they can get. I was able to turn that control down to about half and I can now turn up the subwoofer output on the deck to a reasonable level without rattling the car apart.


• The amplifier is rated for an impedance of 2 ohms but it will work just fine with a speaker of higher impedance. Impedance is basically the same as electrical resistance but it applies to systems where the current direction alternates. Capacitors and coils have varying impedance depending on the frequency, and that's why they are used for frequency filters and crossover circuits. Right now I have two 4-ohm drivers in the subwoofer box that are connected in a parallel circuit. The total impedance of the system is therefore 2 ohms (see below). If I use a single 4-ohm driver, the amplifier will run cooler and, if I understand correctly, send half the power out as it does now for a given volume level.

I'm still going to go up there next week and discuss the possibility of getting a smaller speaker enclosure with either a single driver, or two smaller drivers. But the worst-case scenario is now that I keep what I have and, now that I've adjusted it, it sounds good. I just won't have the trunk space I would like.

To calculate the resistance/impedance of a parallel circuit, take the reciprocals of the resistance/impedance of each component, add them together, and then take the reciprocal of the total. So, in the case of my speaker box with two drivers, each one is 4 ohms. The sum of the reciprocals is 1/4 + 1/4 = 1/2. The reciprocal of the sum is then 2. If I added an 8-ohm driver, the sum of the reciprocals would be 1/4 + 1/4 + 1/8 = 5/8. The total impedance would then be 8/5 ohms or 1 3/5.