Handbook for Sound Engineers

Loudspeakers 597

17.1 Introduction

A loudspeaker is a device that converts electrical energy
into acoustic energy (electroacoustic transducer), or
more generally, a system consisting of one or more such
devices. Loudspeakers are present in our daily lives to
such an extent that, in most modern societies, one is in
almost constant contact with them. From the time the
speaker in our clock radio wakes us in the morning until
we turn off the television before we go to bed at night,
we encounter loudspeakers almost constantly. Even our
computers have loudspeakers.

A general treatment of loudspeakers, including their
history and design considerations, in order to fit within
a single chapter of a book such as this, is limited to
providing an overview of the subject rather than an
in-depth treatment of design and theoretical consider-
ations. We will touch on as many of the relevant areas
as available space permits, while providing references
for the reader who is interested in further study. This
chapter may serve as an overview of the subject for end
users and audio enthusiasts and as a guide to further
study for those interested in performing loudspeaker
design work themselves.

17.1.1 Uses of Loudspeakers

Even though there is a very wide range of applications
for loudspeakers, they may be thought of as serving
some combination of four primary purposes:

1. Communication.


2. Sound reinforcement.


3. Sound production.


4. Sound reproduction.

While there are common requirements for all of
these uses, each one also imposes its own demands on
loudspeaker attributes. In a given application, it is
possible that more than one of these purposes must be
served by a single loudspeaker. In such cases, the suit-
ability of the loudspeaker for one or more of its uses
may be compromised in order to facilitate others.

Communication. Ranging from intercom systems in
offices and schools to radio communications systems
for the space shuttle, voice communication systems
make our everyday lives safer and more convenient.
The first practical loudspeaker was in the earpiece of the
original telephone. Since that time, loudspeakers have
been an integral part of voice communication systems,
from intercom systems to satellite-based telephone and
conferencing systems.

Sound Reinforcement. In numerous situations

involving public speaking and musical performance

before audiences in halls, auditoriums, amphitheaters,

and arenas, the sound created by the voices and/or

musical instruments is not of sufficient loudness to be

heard or understood satisfactorily by everyone present.

In such situations, a sound reinforcement system can

provide the acoustic gain required to overcome this

deficiency.

Sound production. There are a number of subcatego-

ries of this type of loudspeaker usage. Perhaps the most

readily recognizable is the use of amplification as an

integral part of certain musical instruments—e.g., elec-

tric guitar, bass, and keyboards. Other examples include

emergency warning and sonar systems. Loudspeaker

characteristics may be very highly specialized when

they are used as part of a sound production system, and

loudspeakers optimized for this type of use are often not

well suited to other uses.

Sound Reproduction. Playback of recorded music,

motion picture soundtracks, and videotape requires a

sound reproduction system. Almost every home in the

United States has one or more sound reproduction

systems. Movie theaters and recording studios also

require sound reproduction systems. One of the author’s

past design projects was a loudspeaker system for use in

an international chain of large-screen specialty theaters.

17.1.2 Loudspeaker Components

It is useful to identify the component parts (or subsys-

tems) of a loudspeaker for individual examination and

analysis. For purposes of this chapter, the components

of a loudspeaker are:

1. Transducer.


2. Radiator.


3. Enclosure.


4. Crossover.

We will examine various forms of each of these

components in the sections that follow. Their interac-

tions with each other within a loudspeaker will be

discussed. We will also present concepts of loudspeaker

performance characterization and an overview of elec-

troacoustic models. The reader is encouraged to pursue

the subject matter that is presented here through the

references provided in the bibliography. The design and

analysis of loudspeakers is a multidisciplinary field,

incorporating elements of music, physics, electrical and

mechanical engineering, and instrumentation. The indi-

vidual subject areas are challenging and fascinating in