About AUDIO

As we each spend more time commuting in our cars daily, a good audio system in the car is becoming less of a luxury and more of a necessity. There are days when, faced with the snarling Malaysian traffic, many of us would agree that the only thing keeping us sane is the music swirling within the interior of our vehicles. Whether your taste ranges from classical to pop, or orchestra to rock, a good car audio system lets you gain maximum enjoyment from your favourite tunes.

Many of today's vehicles come with adequate audio systems. Gone are the days of tinny speakers and cassette players. But for the discerning listener who is considering an upgrade, here are some issues that you might want to consider:

1. How much time do you spend in the car? For some people, a single-disc CD player might be sufficient, but for continuous, uninterrupted listening, nothing beats a 6-disc or IO-disc CD changer.
2. How much money are you prepared to spend on the system?
3. How much vehicle space are you willing to give up to accommodate the system?

BASIC UNIT
To quote my mechanic when I was contemplating upgrading my audio system,"Who on earth listens to cassettes these days?". Consequently, CD players are becoming more of a norm. Many new models these days come with a standard CD player instead of cassette. Regardless, a good head unit will have the following qualities:

1. It utilises four channels to drive four speakers.
2. Separate bass and treble controls that will allow you to tailor the sounds to your taste.
3. Pre-amp outputs to run amplifiers without conversion. This will actually deliver a cleaner sound.
4. Fully or partially detachable face plates. This is an oft-overlooked security feature that might actually deter thieves from breaking into your car to steal your audio unit.

When selecting a head unit, pay attention to the frequency response . A reasonable figure would be 30Hz - 15KHz +/-3bD. Obviously, the wider the frequency response, the better; and the higher the FM sensitivity of the head unit, the easier it will be for the unit to pull signals in remote areas.

AMPLIFIERS
The task of the amplifier is simply to amplify the signal from the head unit before passing it to the speakers. Amps can be classified into 4 types:

1. Class A amp - this utilizes only one output transistor, which works all the time and generates the most accurate sounds. However, the heat generated from this amp requires built-in cooling fans to be incorporated into the amp design, resulting in big and expensive amplifiers that might not be required in an enclosed environment like your car.
2. Class B amp - the Class B amplifiers uses two transistors, one for positive signals and one for negative signals. Both signals are then combined which can cause a small amount of;"crossover distortion. One of the biggest advantages of the Class B amplifier is, the use of two transistors results in less heat being generated, making smaller and more efficient '"- designs possible.
3. Class A-B amp - uses a hybrid of both Class A and Class B methods.At low volumes, this amplifier functions in Class A mode.At high volumes, Class B mode is employed.
4. Class D amp- this top of the range amp samples signals at high rates and reconstructs them at high volumes. This method generates no heat but requires a lot of cash. The power required to drive mid-range to high-frequency speakers i are normally around 30 to 50 watts per channel. For subwoofers, 80 - 150 watts is normal. Ideally, power output should be matched to what it will be used for and the type of speakers that the amplifier will be driving.

Each possible location to house the amplifier comes with its own pros and cons:

1. Glove compartment
   Pros:
   . Very close to power source
   Cons:
   . Wasted glove compartment space
   
2. Under the front seat
   Pros:
   . Best security
   . Shorter power wiring required (because the amplifier is located nearer to the battery)
   . Minimal voltage drop
   Cons:
   . Generates higher temperature because there is limited airflow under the seat
   . You will have wires running under the carpet
   . Car seat must be removed for installation
   
3. Boot
   Pros:
   . Good security
   . Better ventilation (as compared to under the seat)
   . Easy installation
   Cons:
   . Might sustain damage as heavy things are loaded and unloaded into the car
   . Possible higher loss of power due to wire resistance caused by the need for longer RCA wires

You can compare amplifiers by using the RMS power rating (use the same parameters, e.g. ohms rating). Most amplifiers are at least 4-ohm stable, meaning that the amplifiers can continuously handle power loads of 4 ohms per channel. 4-channel amplifiers are obviously a better choice than 2-channel amplifiers. The reason is, a 4-channel amplifier can drive four speakers and leave room for future expansion.

When buying amplifiers, don't be misled by the labels. In most cases, the more powerful the amplifier is, the bigger its heatsink will be to dissipate the heat generated. However, there are cases where manufacturers build bigger heatsinks than is necessary to give an illusion of power to the amplifier.

SUBWOOFERS
For rock fans, subwoofers are a necessity to generate that thumping earth-shaking bass that is the mainstay of the genre. Subwoofers demands one and a half times more power from the amplifier. Physically, a subwoofer can range from 20cm to 40cm in size. Generally, the rule of thumb is, the bigger the subwoofer, the deeper and louder the bass output. Unfortunately, this means that more space is required.

All speakers produce front and rear waves that disperse differently according to the size of the speakers. In the case of subwoofers, the dispersion pattern is so huge that the front and back waves must be separated. Hence, the need for enclosures. There are essentially 3 different types of enclosures:

1. Free-air subwoofer - this type is either mounted under the rear deck and discharging upwards, or mounted behind the back seat and hammers forward.
   Pros:
   . Saves space
   Cons:
   . Needs more power and may not sound as good
2. Ported box - essentially, a box with a port to release air. Produces louder sounds but must be built according to the manufacturer specifications or you might end up with a 'muddy' sounding subwoofer.
3. Sealed box - this is the most common type of enclosure. Gives out a good tight bass, but like the ported box, the size must be in accordance to manufacturer specifications.

SPEAKERS
High-end speakers are able to reproduce exceptional sound and strong musical imaging. Good speakers are made of strong magnets and heavy-duty coils; designed to handle high volume better than the cheaper paper cones of inferior brands. Speakers come in a variety of sizes, each designed to produce sound in a certain frequency range:

1. Coaxial speakers - a collection of two speakers in the same housing with a simple crossover. One plays high while the other plays the mid-bass frequencies. This system, however, lacks flexibility.
2. Separates - consists of a tweeter and subwoofer and usually comes with crossover network. Separates are more expensive but are capable of producing better sounds.

Round speakers are also better than oval ones as they are more rigid and less likely to distort at high frequencies. Most oval speakers are mainly used when space is a constraint. It is also advisable to avoid speakers with magnets that are too heavy. The average amplifier will have a lot of trouble driving these types of speakers.

When looking at the technical specifications for speakers, it is generally advisable to aim for higher RMS power, frequency response and sensitivity figures. 30 to 50 watts are usually sufficient for the front and rear speakers but subwoofers are going to need 100 to 150 watts each. Other speaker terminologies:

1. Input sensitivity - this refers to sound pressure level and how loud the speaker will play given certain input.
2. Frequency response - refers to the range of frequencies that the speaker can reproduce within a power range.
3. Nominal handling power - refers to the continuous power handling capability of the speakers.
4. Peak power handling - maximum level of power that the speakers can accommodate.
   

JUDGING AUDIO SYSTEMS
Your ears are still your best judge. Bring along a favourite CD to test the speakers.
STEP 1
Begin with light and soft music (perhaps an instrument solo). This will help to detect any system noise.
STEP 2
Switch to something more complicated. Listen to make sure that the output does not sound hazy.
STEP 3
Finally, listen to something familiar and see how faithfully the sounds are being reproduced.


Article contributed by AAM