Neko
Pit Crew Chief
Aug 19, 2004, 6:21 PM
Post #1 of 1
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Choosing The Right Amplifier
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The most common question a newcomer to car audio would almost certainly ask is what is the best amplifier?.
There are several factors to consider when purchasing an amplifier.
The first question would be what kind of speakers need the amplifiers?. In car audio, there are different speakers for different frequencies. High frequencies would be produced by tweeters, mid frequencies by mid range and low frequencies are taken care of by subwoofers.
Generally, tweeters and midrange can come in two styles. One is of the coaxial type, and the other is of the component type. The coaxial is a two-in-one speaker, with the tweeter within the larger cone. Components would have two separate speakers that come with a crossover (xover).
These two types need about 100watts RMS to produce clear sounds. Rule of thumb is: The higher the power, the cleaner the sound. These would only require amplifiers that are rated at roughly 100w @ 4ohms.
Unless you are about to enter competitions, there is no need to go higher. 100watts would almost certainly provide clean and loud sounds.
Subwoofers, on the other hand, require more power to push them to work. Low frequencies require more air to be moved, and that is why subwoofers are so large. A typical entry-level subwoofer might only require 200watts RMS, and the high power subwoofers can handle 1,000watts and beyond.
Amplifiers, especially subwoofer amplifiers, draw a certain amount of power from the cars alternator. A typical 100w amplifier will not draw a lot of power, but 600w amplifiers might draw over 50amps. There are a number of amplifiers that are in different class. The first is class A, with a high draw in power. A/B and B are more common types for low power (under 500w) amplifiers. Class D is the most common for amplifiers rated 600watts and higher. This is because their topology allows less draw while creating the same amount of power, as opposed to a Class A amplifier. Class D amplifiers make a significant amount of noise with high frequencies, so that would explain why it is only used in subwoofer applications.
For midrange and tweeter speakers, the connections are simple enough. Positive to positive, negative to negative. Majority of car audio speakers come in 4 ohms, and there is little to worry about in terms of load.
It is a different story with subwoofers, as subwoofers produce a mono signal. All amplifiers have the ability to be bridged, basically taking the two channels into one single mono channel.
Commonly, you would see (2channel) amplifiers with the following power ratings:
RMS @ 13.8v
100w X 2 @4ohms
200w X 2 @2ohms>
400W X 1 @4ohms
RMS denotes the continuous power that the amplifiers produce at 13.8volts. 13.8 volts is what car batteries commonly produce.
The first set of numbers mean that the amplifiers will produce 100watts to each channel with 4ohm speakers connected. Similarly, 200watts will be produced with 2 ohm speakers (usually two 4 ohm speakers on one channel). The last number is only relevant should the amplifier power subwoofers that handle 400watts RMS.
Take note that with a mono channel (x1), it is written as 4ohms again. Amplifiers have limited capabilities in ohms. The ohm level can make or break an amplifier. The lower the ohm figure, the more power amplifiers can produce. In the case of the amplifier mentioned above, only a 4ohm load can be accepted. You could connect it to a 2ohm load, but you would most probably overwork the amplifiers until they either shutdown or burn out. Unless the amplifier specifically states that it can drop lower, do not try to get more out of your amplifier.
Judging by the ohm loads, it is easy to see why it is rather hard to choose subwoofer amplifiers. The amplifier and the subwoofer have to compliment each other. For the above amplifier, a 4ohm single voicecoil (covered in Subwoofers) subwoofer with 400watt RMS handling would be ideal.
Do take note that well respected amplifier manufacturers underrate their amplifiers, whilst cheaper amplifiers would over rate their power to attract more people. Under rating amplifiers has been a common practice, so that during competitions, they can enter a slightly lower class for a little advantage.
(This post was edited by Neko on Aug 19, 2004, 6:21 PM)
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