It happens: A buddy of yours brags that he just got a 1000 watt amplifier, new in the box, for $100. Sounds too good to be true yet you rush over to the flea market booth to check out this “deal of a lifetime” before they are all sold out. Yes, there it is, 1000 watts is written all over the box and the amp – so it has to be true. They couldn’t do that if it wasn’t really a 1000 watt amp could they? This article will help take some of the guesswork out of car audio amplifier specs.
FTC to the Rescue – NOT!
To combat false advertising problems, the Federal Trade Commission mandated a uniform amplifier measurement standard all the way back in 1974. Amplifiers must be rated for RMS (root-mean-square) power, however these numbers are usually buried somewhere in the spec sheet. They can still print whatever they want on the amplifier for “marketing” purposes. So , how do you know if you’re getting a good deal? Here are the numbers that you need to look for.
A true amplifier rating would be something like “50 watts X 2 RMS into a 4 ohm load with less than .1% THD from 20Hz to 20kHz.” All four ratings are necessary to make a true apples to apples comparison. Peak power ratings are useless. Many of us in the car audio field call them “ILS” ratings because the only way that amplifier is going to do that 1000 watts is “If Lightning Strikes” – and then only for a millisecond!
Prepare for Resistance!
The RMS power is the most important, but to be fair you also need to know what impedance, or ohm load, is being used. The lower the impedance, the less resistance the amplifier sees, which usually means higher output power. In theory, an amp would produce twice the power into a 2 ohm load than it would a 4 ohm load, but the power supply on most amps won’t produce that much extra power.
For most amplifiers running mids and highs you will be running a 4 ohm load so that rating will matter the most. For a subwoofer amplifier you will need to know what subwoofer setup you will be running, and if you will be bridging a stereo amplifier to one channel, or perhaps running a mono amp. Once you know the load, you can look for the appropriate specification to be able to accurately compare different amplifiers. If you will be at a 2 ohm load then that is the only rating that will matter to you.
The next number to look at is the THD or total harmonic distortion. You will hear anything above 1%, but most amplifiers will be much lower than that. If the manufacturer rates the output at a distortion higher than 1% then it will not be useable power, since nobody would want to listen to that much distortion for very long.
What’s the Frequency?
The last number to look at is the rated frequency range. Some manufacturers will rate output at an easy 1kHz test tone. Since bass requires the most power to reproduce, rated power at a single test tone will not be a very good real world comparison. Make sure that the rated power goes all the way down to 20Hz – the lowest frequency that you can hear and the most demanding. If it is a dedicated monoblock or subwoofer amp it may only be rated up to a few hundred hertz, but that is not as critical since the higher frequencies are less stressful on the amp.
Amplifier Specs The Driven Way
Once you know the real numbers you will be able to tell if that “1000 watt” amp is really the deal that you thought it was.
At Driven Sound and Security, we don’t play games with our car audio amplifier specs. We show you what is real. We match your amplifier to your speakers or subs and create a perfect fit. This is not just our way of doing things, it is really the only way if your goal is a quality sound system for your vehicle. Stop in and let us show you what we are talking about!