Crossovers De-mystified Why Are There Different Sizes of Drivers? Fig. 1 Fig. 2

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Loudspeakers Loudspeaker systems come in many shapes and sizes, from the Hi-Fi in your home to a concert system at Wembley Stadium. Despite the difference in size between these systems they all do the same job; converting electrical signals into sound that we can hear (see figure 1). How do they do that? When a loudspeaker cone moves, the air in front is compressed and then expanded, creating a sound wave. It is these compressions and expansions that transmit the sound from the loudspeaker to the listeners' ears. In most loudspeakers this conversion from electrical energy to sound energy is achieved by using a moving coil design. The electrical signal is passed through a tightly wound coil of wire which is placed in a magnetic field, as shown in figure 2. The alternating current passing through a magnetic field causes the coil to move, displacing the cone (or diaphragm) backwards and forwards, generating sound. If you remove the grille from a typical Hi-Fi speaker, you will see two different sized drivers inside. We accept that the larger of these is for bass frequencies, and the smaller for treble, but why is it necessary to have these two drivers? To reproduce bass frequencies, a large volume of air must be moved. This is done by allowing a large amount of movement in the driver, and also by increasing its size. As the size is increased, the effectiveness of reproducing high frequencies is reduced as it becomes more difficult for the cone to vibrate at the speed required. High frequencies generally require less energy to be transferred to the air, and so much smaller drivers can be used. These smaller, lighter drivers can vibrate very


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