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Loudspeaker Tutorial

The most common type of loudspeaker is the MOVING COIL speaker, where a coil of wire is suspended in the magnetic field of a circular magnet. When a speech current is passed through the coil a varying magnetic field is generated by the coil. The two magnetic fields interact causing movement of the coil.

loudspeaker internal diagram

The movement of the coil causes a cone, which is attached to the coil, to move back and forth. This compresses and decompresses the air thereby generating sound waves. The loudspeaker is a TRANSDUCER converting one form of energy to another.

Loudspeakers have Impedance, typically 4 or 8 ohms. This must be matched to the output impedance of the amplifier.

Loudspeakers are mounted in enclosures (boxes). The design of enclosures is very complicated.

Large speakers cannot reproduce high frequencies and small ones cannot reproduce low frequencies. Therefore two speakers are used, a large one (a Woofer) for low frequencies, and a small one (a Tweeter) for high frequencies.

To ensure that the correct frequencies go to the desired speaker, a Crossover Unit is used. In the diagram, C1 and L1 are a low pass filter. C2 and L2 are a high pass filter. (there is a page on FILTERS).

When using two speakers together, as in stereo systems, they must be in phase. This means that they move out and in together. This happens if the speaker leads are connected correctly.

LOUDSPEAKER circuit diagram

Speakers can be connected in series and parallel but the total impedance must match the amplifier impedance. Using a lower impedance than the correct one can blow up the output stage of your amplifier.

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