Speaker Construction

Speaker Construction

Speakers are a very important part of a sound system. No matter how good the receiver or CD player is,

the sound quality will be

Construction of a speaker

reduced if inferior speakers are used. Equally, if the speakers are of a lower power output rating than the set, distortion will result at best and damage to the speakers at worst. Speakers fall into the following categories:

Tweeters - high frequency reproduction Mid-range - middle range frequency reproduction (treble) Woofers - low frequency reproduction (bass) Sub-woofers - very low frequency reproduction.

Radio Data System (RDS) RDS has become standard on many radio sets. It is an extra inaudible digital signal, which is sent with FM

RDS display

broadcasts in a similar way to how text is sent with TV signals. RDS provides information so a receiver can appear to act intelligently. The possibilities available when RDS is used are as follows:

The station name can be displayed in place of the frequency

Automatic tuning to the best available signal for the chosen radio station

Traffic information and news broadcasts can be identified and a setting made so that whatever you are listening to at the time can be interrupted.

Radio Reception ฀฀ There are two main types of radio signal transmitted: amplitude modulation (AM) and frequency modulation (FM). FM is generally a better source of high fidelity sound. This is because the quality of AM reception is limited by the narrow bandwidth of the signal. FM does however present problems with reception when mobile. As most vehicles use a rod aerial, which is omni-directional, it will receive signals from all directions. Because of this reflections from buildings, hills and other vehicles can reach the set all at the same time. This can distort the signal.

Digital Audio Broadcast (Dab) Digital audio broadcasting is designed to provide high quality digital radio broadcasting for reception by

Digital

stationary and mobile receivers. It is being broadcast

radio set

designed to operate at any frequency up to 3GHz. The system uses digital techniques to remove redundancy and perceptually irrelevant information from the audio source signal. All transmitted information is then spread in both the frequency and the time domains (multiplexed) so a high quality signal is obtained in the receiver, even under poor conditions.

Auto PC A revolution in the use of information technology in vehicles is taking place. Advanced computing, communications and positioning

In car

developments are being introduced in even the most MP3Player basic vehicles. Shown here is an ‘Auto PC’/’Car

Multimedia’ system. Many leading computer companies, including Microsoft, IBM, and Intel have identified the vehicle as their next big marketplace. Plans have been announced for in- vehicle computers with a range of integrated functions. Microsoft’s Auto PC, for example, uses a cut-down version of the standard Windows operating system.

Functions The Auto PC will be able to run familiar desk-top programs whilst also offering the following:

Spoken turn-by-turn navigation

Navigation display

Digital map database of useful sites, such as filling stations and cinemas

Voice memo system Vehicle diagnostics program Vehicle security and tracking system Emergency roadside assistance service High-performance stereo system capable of

playing CDs and receiving FM radio. Mobile Communication Tying the computer in with the mobile

communication system opens up even more possibilities. Cellular phone systems can provide an excellent means of tracking vehicles. Phone operators divide the country into separate cells and monitor phones as they move between them to ensure that each phone communicates through the best transmitter. Mobile communication systems will have a profound impact on how vehicles are used. Development work is underway on the exchange of information between vehicles and the road infrastructure.

Cell Phones The first car telephones, which were so large, had the main unit fitted in the car boot! If the success of the cellular industry is any

Mobile phones

indication of how much we can make of the are

everywhere!

telephone, the future promises an even greater expansion. Cellular technology, which became useful in the 1980s, has continued to develop. In vehicle communication equipment for normal business and personal use, will be by the simple pocket sized mobile phone and there is no further market for the car telephone. Hands free conversions will still be important.