Car Stereo Amplifiers

The most common basic audio entertainment is the Radio/tape player units with about 10 W per channel built in amplifier. Many come with CD players and CD changers too which go under the name of Head Units. But most people these days sport small handheld MP3 players or Ipods which can hold one GB or more of storage capacity. As a result of the popularity of these MP3 players, the current crop of head units contain USB ports to mate with these audio units. Some even come equipped with WiFi and bluetooth for added connectivity.

To unravel the bewildering array of in-car entertainment we provide below the terminologies and some details.

Power Amplifiers:

S-MOSFET Power chips use Silicon On Insulator (SOI) - a recent improvement on the MOSFET - Metal Oxide Field Effect Transistor technology. Shorn of technical terms, it improves the signal to noise ratio in addition to reducing the distortion levels. Sony Xplod series of car stereos sport such S-MOSFET power chips. The typical s/n ratio of 120 dB is claimed by Sony for these amplifiers.

Typically most car units will provide 50 W (rms) per channel. With four channels (2 sets of identical Stereo) a head unit is capable of providing a peak output of around 400 W (combined peak music power output) into the rated 2 Ohm speaker load.

Most amplifiers use bridge mode configuration to supply the maximum power with the normal 12 V supply available in a car. Some very high powered amplifiers to drive subwoofers use Switch Mode Power Supply Units to increase the available power supply. Most amplifiers driving Sub woofers will be rated at least 300 W rms (1200 W peak music power).

Signal to noise Ratio:

Briefly noise is the "hiss" you hear when you turn up the gain of the amplifier before a song starts. Digital formats put very little noise compared with analogue formats. Cassette players use Dolby noise reduction systems to mask the noise level in an active manner. Typical tape players have about signal-to-noise ratio of around 30 dB without any active noise reduction system. CD and other digital formats have a much better s/n ratio upward of about 60 dB. In other words, in plain speak, it boils down to this - the signal is one million times greater than the noise level. Don't just get too impressed with this s/n level yet. This s/n is applicable to head units - source alone. When you deal with audio systems you must realize one thing - each component is like a link in a chain. The weakest link will still bring down the whole effect. Amplifiers must exhibit better consistent overall s/n ratios at the full volume level. Many small amplifiers would choke when asked to reproduce bass tones at full blast.

Wow and Flutter:

Wow is a change in pitch you hear with tape decks /cassette players and flutter is the cyclic variations owning to mechanical imperfections in the tape transport system. If your car cassette player has a dirty capstan or pinch roller - the degradation in the sound quality will be pronounced.
Thankfully Wow and Flutter is not such a worry with digital systems any longer.

Car Speakers:

This is one link which can make or mar the whole car audio systems. Generally you pay what you get. The heavier the speaker drive unit is the better - other things being equal. The main points to consider here is the power handling capacity, the sensitivity and the frequency range.

The Sensitivity: The more the sensitivity the louder it will sound for a given input. With modern injected Polypropylene Diaphragm designs and ferrite magnet assemblies you will get typically in the regions of over 85 dB/W/m.

Frequency Range: No one size fits all frequencies. This is where speakers are classified as per their range of response -


Tweeters - to handle high frequencies above 6 KHz

Mid Range (Squakers) - to handle mid range frequencies between 800 Hz and 6 KHz

Woofers - to handle low range frequencies - 200 to 1 KHz

You can't feed the speakers directly again - you need a matching cross over network. Most car speakers come with a built in multiple speaker units in a single package specifically to obviate this need of matching.

Sub Woofers: These are monster sized units which handle lots of power and need to reproduce frequencies in the region of 30 to 800 Hz. They can deliver heart thumping low frequency tucked away in any remote corner of your car.