Thursday, December 27, 2012
Fundamentals of Car Speakers – Part 1
Speakers, the final link your car's audio system, is driven by the amplifier. Basically, a speaker works by creating air pressures of different frequencies and of different degrees. When electrical impulses from the amplifier reach the voice coil (attached to the cone of the speaker), the latter becomes magnetized. As the current alternates between positive and negative, the magnetized voice coil will either be attracted to or repelled by the fixed magnet at the bottom of the speaker. As a result of the attraction or repellation, the voice coil moves the cone, creating sound.
Two concepts related to speakers are "imaging" and "staging". Imaging is the ability to produce different sounds from the same place. When speakers are well-placed and of high quality, the sounds seem to come from different instruments and voices. Staging is the audio illusion that everything is in front of the listener. The right speaker location and direction are necessary for good imaging and staging.
There are several types of speakers: coaxials and separates (such as midbases, subwoofers, horns and centre channels). They were invented not because car audio manufacturers want to sell unnecessary products but because a single speaker cannot produce all sounds accurately. Therefore multiple speakers are necessary, each reproducing sound in the frequency range it was designed for.
A coaxial speaker consists of two or more speakers, including a crossover, built within the same frame. (A crossover is a device that takes a full range signal and divides it into different frequency ranges). Separates consist of a tweeter, woofer and an external crossover. Mid-bases handle frequencies in between those handled by tweeter and subwoofers. Subwoofers add low frequencies to the whole system. Horns, usually mounted under the dashboard, play mid and high frequencies and are more expensive than conventional speakers. When used, tweeters can be dispensed with. Center channels play a mono signal to create the audio illusion of singers being in front of the car.
Coaxials are often not as good as separates. Separates give you greater control over your imaging. For rear fill applications, however, coaxials perform well as imaging is not a primary concern. ("Rear fill" refers to the presence of depth and ambience in music).
Speakers come in various sizes, according to the frequencies they handle. As the wavelength of a 20,000 Hz signal is very small, it should be obvious that speakers which handle high frequencies are very small. Generally, the bigger the speaker, the lower it goes.
A subwoofer plays low sounds (particularly bass notes), such as those having frequencies below 120 Hz. On the other hand, a tweeter reproduces high frequencies ranging from 6,000 to 20,000 Hz.
Midbases play from around 50 Hz to 500 Hz. In terms of size, tweeters are half to one inch (in diameter); centre channels, three or four inches; midbases, from five to six inches; and subwoofers. from l0 to l8 inches.
Most speakers are round but a few are oval. Though a round speaker sounds better, an oval speaker -- by virtue of its bigger area -- is more efficient at producing bass. However, since it is less rigid compared to a round speaker, the former will distort more.