A
loudspeaker produces sound by coverting electrical signals from an audio amplifier
into mechanical motion. Sound is created
from the forward and backward motion of the loudspeaker cone (Fig. 1), which is a concave
plastic or paper disc that may be
a few inches to over a foot in diameter.
The cone is mounted and centered on a concave metal frame by a ring of flexible rubber or suspension. Glued to the center of the cone is a hollow
cylinder of thin, lightweight aluminum, typically one inch long and one inch
in diameter, called the bobbin. A length of thin, insulated wire is wound upon
the bobbin to form the voice coil;
both ends of the voice coil wire are connected to the voice coil terminals on the frame. The voice coil is positioned inside a narrow
cylindrical groove or air gap
in the center of a magnet. The coil is suspended in the air gap by a flexible
fabric disc or centering device.
An audio amplifier is connected to
the voice coil terminals. The coil
emits a magnetic field as audio signals from the amplifier travel through
the voice coil wire. The voice coil field alternately pulls and pushes the
coil, bobbin and cone assembly towards and against the magnetic field from
the magnet, which causes the forward and backward cone motion.
The function and relationship of each component must be
explored in detail to understand the electromotive properties and limitations
of the loudspeaker.