RC-Monster Forums - View Single Post - Car audio question about amps and speaker ohm rating

BrianG · 09.30.2009, 12:15 PM

You have to remember a few things about car audio amplifiers:

1: They require high current that has to be delivered over a much longer distance (typically from the front where the battery is, to the trunk where the amp is). Required wire gauge is a function of distance and current. R/C wires are MUCH shorter so can get away with smaller wire.

2: Your typical class A-B amplifier is around 60% efficient. So, if you have a true 500w amp, it is actually pulling 833w from the battery at full-tilt. Assuming a steady 14.4v, that's almost 58A.

3: Related to #1, wire has resistance. The larger the wire, the less the resistance. Resistance creates voltage drop. Let's say a 12GA wire has 0.002 ohms of resistance per foot, and it takes 16 feet to get to the amp. At 100A, that would be a 3.2v drop on just the wire. So, instead of 14.4v getting to the amp, you are getting only 11.2v. Larger gauge wire has less resistance, so there is less voltage drop and the amp runs better.

	(#11)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	09.30.2009, 12:15 PM You have to remember a few things about car audio amplifiers: 1: They require high current that has to be delivered over a much longer distance (typically from the front where the battery is, to the trunk where the amp is). Required wire gauge is a function of distance and current. R/C wires are MUCH shorter so can get away with smaller wire. 2: Your typical class A-B amplifier is around 60% efficient. So, if you have a true 500w amp, it is actually pulling 833w from the battery at full-tilt. Assuming a steady 14.4v, that's almost 58A. 3: Related to #1, wire has resistance. The larger the wire, the less the resistance. Resistance creates voltage drop. Let's say a 12GA wire has 0.002 ohms of resistance per foot, and it takes 16 feet to get to the amp. At 100A, that would be a 3.2v drop on just the wire. So, instead of 14.4v getting to the amp, you are getting only 11.2v. Larger gauge wire has less resistance, so there is less voltage drop and the amp runs better.