618 Chapter 17
involved in the design of the component parts. The
system designer’s challenge is to make a collection of
individual components function as a cohesive whole
while meeting the cost, size, and aesthetic requirements
of the loudspeaker’s intended applications. The design
of a successful loudspeaker system involves much more
than simply selecting a group of components and
building a box to house them.
It is axiomatic that, in addition to the required tech-
nical expertise, a loudspeaker designer should have the
capability of subjectively evaluating a loudspeaker’s
performance—critical listening—and that the final
determinant of a loudspeaker’s success will almost
always be subjective acceptance. It is equally true that
there are always objectively observable phenomena that
correlate with subjective preferences. The difficulty in
reconciling the two is a direct result of the very large
number of objective elements that must be accounted
for in order to fully characterize the performance of a
loudspeaker. This subject is covered in greater depth in
the “Loudspeaker Characterization” section of this
chapter.
Loudspeaker systems are often categorized by the
number of spectral divisions made in the system, as in
two-way or three-way systems. Generally speaking, a
loudspeaker system consists of two or more trans-
ducer/radiator combinations, a crossover network, and
an enclosure that houses everything. In addition to
providing a convenient package for the components, the
enclosure serves structural, acoustic, and aesthetic
purposes. The sections on acoustic boundaries and elec-
troacoustic models provide information about some of
the acoustic effects of enclosure design.
17.8.1 Configuration Choices
A number of decisions about a loudspeaker’s config-
uration are typically made early in the design process.
These include:
- The number of spectral bands, or divisions.
- The type of radiator to be used for each band.
- The location and orientation of the individual
components within the system housing.
In determining the number of frequency bands to be
used in a loudspeaker, several conflicting demands must
be reconciled. Choosing a greater number of divisions
creates the possibility of greater broadband acoustic
output and more optimal radiator configurations for
each band. On the other hand, each added band adds to
the size, complexity, cost, and more often than not, to
non ideal aspects of the acoustic behavior of the
finished design.
The type of radiator chosen for each band is often a
matter of custom or convention rather than of engi-
neering. Where possible, it is generally desirable to
match efficiencies and directivities of adjacent bands
over a range of frequencies centered about their cross-
over point. This is most readily accomplished when
similar types of radiators are used for both of the bands
in question.
The location and orientation of individual compo-
nents is an area worthy of careful attention. It is
common practice to place all of the transducers on a flat
panel (a baffle), displaced from each other in vertical
and/or horizontal directions. In the case of loud-
speakers designed for stereo reproduction, it is also
common practice to make pairs of speakers in a
mirror-image layout.
The aforementioned common practices have devel-
oped over many years, with the primary motivation
being cost and ease of manufacture. Another approach
to loudspeaker system design is the coaxial layout. First
employed in the earlier part of the 20th century, this
practice involves locating two or more bands of a loud-
speaker along a common axis. While the coaxial
approach is typically more difficult to implement, it has
some advantages over more conventional layouts.17.8.2 Types of Loudspeaker SystemsThe simplest form of loudspeaker employs a single full-
range transducer to reproduce all frequencies. The most
common applications for this type of device are
limited-bandwidth (e.g., speech) systems and inexpen-
sive music reproduction systems.
For residential music systems, one of the more
common configurations is a two-way system utilizing a
small (typically 6 or 8 inch) woofer and a dome tweeter.
Fig. 17-41 is one such system. More elaborate (and
costly) systems are also employed for residential use,
some employing line arrays (see Section 17.8.4) of
transducers for one or more of their bands. As is the
case with professional loudspeakers, visual aesthetics
can play as important a role as performance in setting
design requirements.
One of the more common types of loudspeakers for
general sound reinforcement use is a two-way system
consisting of a direct radiator woofer and a
horn/compression driver high-frequency subsystem,
with the components being located one above the other
on the front face of the enclosure. The typical package
for this type of loudspeaker is a trapezoidal enclosure.