Car Amplifier Buying Guide: Powered by ConsumerGuide and HowStuffWorks

The Basics: Car Amplifiers

Sometimes, you just need to crank up the volume. Car audio systems must overcome a good deal of ambient noise--a vehicle traveling down the highway in the company of other loud engines is surrounded by a high background noise level. Factory-installed head units have a modest amount of amplification (generally about 10 watts per channel or less), and many aftermarket head units have at least twice that. The more power the amp included with your CD or cassette player delivers, the cleaner the sound from the speakers. But be careful--a receiver rated at 50 watts maximum power probably has no more than 20 watts of clean power. For that reason, serious mobile listeners eschew the modest amplifiers built into head units and instead opt for powerful external amplifiers.

How to Shop

For the easiest and typically least expensive installation, look for a single amplifier to power all the speakers in a car system. This would be the number of channels listed on the amp, as a single channel is only capable of powering one speaker. Moreover, look for an amplifier that contains its own crossovers; these circuits split the music frequencies so (for example) the highs go to the front speakers while the lows go the rear speakers. This helps maximize power delivery to the speakers and improve sound. When shopping, look at the way an amplifier lets you control these crossovers. Some use rotary controls, while others have less accessible inset controls requiring a screwdriver for adjustment.

You could consider amplifiers with one, two, or four channels, but you'll need a channel for each speaker; this soon increases the complexity and cost of the system. Also, if you'll be adding a subwoofer for killer low-ends sound, you'll usually need a separate amplifier. Remember, every speaker will use one channel of amplification. Four-channel amps are, by far, the most popular.

Amplifiers don't really come with a massive array of features, but there are a few to consider. Soft-start circuitry eliminates the thumps and thuds that can be annoying and potentially damaging to car speakers. Depending on your application, the number of speaker-level and line-level outputs and inputs need to be considered. Make sure you have enough for the setup you are currently installing, while leaving room for at least one future upgrade.

Amps generate a significant amount of heat that affects their efficiency. Numerous methods of dissipating this heat are used--everything from metal fins that create more surface area for air cooling to a few systems that actually use liquid coolant to keep the temperature down. Read reviews and specs to choose between hype and facts.

Biamplification

A system that uses separate circuits of amplification to feed the individual speaker components.

Changers

A CD, MiniDisc, DVD or MP3 unit that handles more than one disc--a multiple player.

Channel Separation

Also known as stereo separation, this is the amount of sound that crosses from one audio channel to the other. The higher this decibel spec, the better the separation is between channels.

Distortion

This is a measurement of the deviation from the original signal to the reproduced signal. Distortion is a harsh sounding artifact that negatively alters the signal.

Dynamic Range

The difference between the loudest peak and softest passage. It can also refer to the spectrum between the edge of distortion at the high end of a product's performance and the product's noise floor.

Equalizer

A circuit or program that changes the frequency response of a signal, boosting or cutting selected ranges from the overall response.

Frequency Response

Also listed as Frequency range, is the spectrum of frequencies produced by a product, within a certain tolerance. For example, a frequency response of 30Hz to 18kHz (+/- 3dB) means a product produces all frequencies from 30Hz to 18kHz without dropping or peaking three decibels. The signal below and above that range does drop off more than 3dB, so the range is really the usable spectrum of sound

Head Unit

The usable part of a component that is mounted in the dashboard is commonly referred to as a head unit. It controls the components, either internally or remotely installed, such as a changer mounted in the glove compartment or trunk.

Impedance

Impedance is commonly listed from 4 to 8 ohms, with some ranging from 2 to 16 ohms. This is a technical description of the amount of inductive resistance a speaker offers to the flow of electrical signals from a receiver. Under normal circumstances, impedance bears no relation to sound quality, but many receivers need a minimum of 4 ohms to work properly. A good receiver may work with 2 ohms, but other receivers or amplifiers will automatically shut off or blow a fuse. If you intend to use two pairs of speakers in parallel from the same terminals, choose loudspeakers rated at least 8 ohms. Also note that speaker impedance ratings are nominal, meaning that a speaker may actually fall below its rated impedance at some frequencies.

OEM (original equipment manufacturer)

This refers to the factory-installed system that comes with a car. Many car manufacturers are using name brand products, either standard or part of an upgrade package.

Power requirements

Different speakers take advantage of different physical properties to produce sound. Too much power can damage speakers, but speaker ratings and amplifier ratings don't always tell the whole story. Speakers rated at 100 watts maximum may safely be powered by a 300-watt amplifier, but if you force all 300 watts into the speaker, the sound will cause you pain and damage the speakers. Too little power can also damage a speaker. If you try to play a low-powered amplifier too loudly it can distort the sound waves, and this distortion can destroy a speaker. Power ratings are listed as either "Peak" or "RMS" (Root Mean Square.) Peak listing in the amount of power the equipment can handle momentarily--a sharp drum hit, for example. RMS is a better indication of the overall performance, because it is a measurement of the average sustained power.

Preamp Output

Generally, an RCA jack that sends the signal to an external amplifier--before the signal is amplified internally.

Sensitivity

Also referred to efficiency. This is a measure of how effectively a speaker can convert electrical power from an amplifier into acoustic sound energy. The higher this number, the more sound you will get at a given volume setting. This is typically measured from one meter away from the speaker with an input signal of 2.83 volts (1 watt into 8 ohms) which results in a sound pressure level, listed in decibels.

Signal-to-noise ratio

The ratio between the audio signal and noise floor. A low number indicates that the noise and music are closer together--the higher the number, the less noise is apparent.

Subwoofer

A large speaker component that produces extremely low-frequency signals, usually below 180Hz.

Surround Sound

This covers many different formats that play sound through multiple speakers to simulate the natural sounds from many locations.

ATTENTION! We recently updated our privacy policy. The changes are effective as of Thursday, October 30, 2008.

To see the new policy, click [here]. Questions? See the policy for the contact information.

Car Amplifier Buying Guide

The Basics: Car Amplifiers

How to Shop

Glossary

Magic Debugger