From DT Online
The loudspeaker is an electro-mechanical device that turns alternating currents into audible sounds. When a signal of sufficient amplitude is applied to the coil it produces a magnetic field which attracts or repels the permanent magnet. This produces movement which is amplified by the diaphragm to give sound.
Features and Applications
Speakers can reproduce sounds in the audio spectrum between approximately 20 - 16,000 Hz.
Small speakers handle high frequencies well, whereas large speakers are mainly suited to low frequencies. A combination of two or more speakers can reproduce frequencies over the whole audio range. Where hi-fi quality is not required, a small speaker will normally suffice.