Page 233 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 11 Acoustic Devices 195

Metal Diaphragm In 1925, Chester Rice and Edward Kellogg of General
Wheel Housing
Horn Base Electric developed what is considered the modern, direct radi-
ating, dynamic loudspeaker. This type of speaker has remained
Electrical
Cabinet principally unchanged since its conception. Figure 11-8 shows
a sectional view of a typical direct radiating, dynamic loud-
Electric speaker. A voice coil is positioned between the poles of a pow-
Motor erful permanent magnet. As a signal is applied to the coil, it is
repelled or attracted to the magnet field in reference to the
polarity and current of the signal. The coil form is fixed to the
base of a conical diaphragm (cone). The cone movement is
Horn driven by the voice coil. As the cone moves, it pumps the air
Figure 11-5 Marine Alarm Horn and creates sound pulses which mirror the electrical signal.
The cone and coil assembly are suspended in a metal frame
with two elements, the surround and the spider. The frame also
Electric horns are particularly common in automotive carries a mounting flange and terminal strip.
applications. They produce a significant signal from a very
compact, inexpensive, and reliable package. Figure 11-6
shows a stylized schematic representation of an electric horn.
Gasket
These units are similar to an alarm horn, except the rotary
hammer is replaced with a solenoid mechanism that is similar
Mounting Frame
in operation to the bell ringer or buzzer. A system like this
allows much higher frequencies and smoother tones than an Front Suspension
alarm horn or bell ringer. The tension of the return spring can (Surround) Schematic Symbol
be adjusted to change the tone of the horn.
Figure 11-7 shows a commercial electric horn such as Frame
might be found on small boats and trucks. These units are also
Outer Pole
an excellent replacement for the OEM (original equipment
manufacturer) horn on most automobiles. Magnet

Loudspeakers Coil Form

Most of us routinely receive audio information from loud- Bridge Piece
speakers. Audio is used in a myriad of applications, such as
radios, televisions, stereo systems, telephones, public address
Inner Pole
systems, walkie-talkies, and even our personal computers.

Hammer Voice Coil
Solenoid Coil
Return Spring Horn Throat Rear Suspension
Point Set (Spider)
Flexible Wire
Horn
Terminals
Metal Diaphragm
Dust Cap
Anvil Cone
Figure 11-6 Electric Horn Mechanism

Metal Diaphragm Figure 11-8 Dynamic Loudspeaker
Solenoid
Housing Horn Base Horn
Horn Throat
The frequency range of any loudspeaker is limited by its
diaphragm mass. To better reproduce sound in certain fre-
quency ranges, designs are created to perform over limited
ranges. Figure 11-9 shows a dynamic loudspeaker that is
specifically designed to reproduce sound in the high fre-
Terminals
quency range. These units are generally referred to as tweet-
Figure 11-7 Electric Horn ers. They are similar to the cone-type unit, except the cone is