Car Parts and Accessories

Installing Auto speakers for the best sound

There is usually space for a speaker behind the dashboard or under the shelf behind the back seat, but if you are fitting speakers yourself, fit them into the doors for best results. However, when drilling holes in the bodywork or door panels, remove the metal filings with a vacuum or compressed air. A AA survey showed that the filings often start severe internal rusting.

There are many different car speakers on the market, some cheap and others more refined. Poor speakers are tiring to listen to, so it is best not to buy a very cheap set.

If your car does not have ready-cut apertures for speakers in the doors or in the back shelf, you will have to cut them yourself. This needs care.

Use the template supplied with the speakers or make one from stiff cardboard, marking the exact shape of the aperture. Remove the panel that is to be cut and carefully trace on to it the outline of the speaker aperture. Use a sharp knife.

When mounting the speaker, make sure that neither its cone nor its chassis comes into contact with any part of the metal bodywork. Fix the chassis firmly, using the cork gasket supplied to insulate the panel from vibrations set up when the speaker is operating.

When two speakers are being used on each side of the car they can be wired together at the output terminal of the radio or, more usefully, through a front/ back balance control.

The leads to the speakers must be connected securely, either by push-on tags or by soldering to their terminals.

Fitting an alternative aerial

A GOOD QUALITY aerial is essential for best reception from a car radio. Some electric aerials have a motor to raise and lower them while others have to be manually raised, but have a small RF signal amplifier to boost the signal. This type of aerial can also boost interference, so it is essential that the car’s ignition and charging systems are comprehensively suppressed. Before fitting an aerial that boosts the signals. For improved FM reception it is possible to buy a helical wound aerial which looks like a two-way radio antenna.

An aerial must be firmly mounted. The junction with the lead must be waterproof and the power wire safely insulated.

Trimming an aerial

MOST CAR RADIOS have an aerial trimmer, which can be adjusted by a screw to give the best reception. On most sets this screw is reached with a small screwdriver after the turning knob has been removed. In this case the aerial can be trimmed after the set is installed. If the screw is reached through a hole in the side or rear of the set, however, the aerial will have to be trimmed before the set is completely installed. To trim the aerial, tune to a weak station at the 500 kHz end of the AM band. With the aerial extended, turn the trimming screw until the best reception of the station is received. The best reception will then be received on all other wavelengths too.

Most interference to car radio reception is caused by pulses radiated at certain frequencies in the radio band from such components of the car’s electrical network as the ignition system (especially the spark-plugs), the dynamo or alternator, the windscreen wiper motor even an electric clock. These pulses are picked up by the aerial or the wiring of the receiver and emerge from the speakers as a crackling sound.

Most cars have had special carbon high tension leads fitted to the spark-plugs to suppress the interference they cause. Other components are suppressed by attaching a capacitor which filters interference between them and earth.

Depending on the position of the aerial and the radio, it may be necessary to fit suppressors to other possible causes of interference. The most common of these are the ignition coil and the alternator.

A further form of interference can be caused by static electricity building up on tyres, wheels or brakes. When this discharges across the wheel bearings or brake components, sharp crackles are heard at the speaker. This can be cured by an expert.

Normally, the metal panels and bodywork of a car act as a screen between the ignition system and the aerial. But with the increasing use of plastic materials in body construction, suppression becomes more difficult. Glass-fibre bodies may require additional screening besides the standard suppression equipment.

This is achieved by covering the underside of the bonnet and engine compartment with metal foil (or an electro-conductive graphite paint) earthed to the metal frame. Alternatively, metal screening plates bolted to the engine may be fitted over the plugs, plug leads and coil to suppress radio interference.

An interference-free radio in a car with a glass-fibre body is difficult to achieve; but experience gained by professional radio-fitting firms enables them to do the work with reasonable success.

In cases where interference persists despite the installation of several suppressors, consult the manufacturer ofthe set for professional advice.

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