Handbook for Sound Engineers

Loudspeakers 617

500 Hz for a wide variety of applications, including
voice-only systems.
The obvious advantage of a folded horn is the
reduced package size for a given horn length. This
advantage is offset by the fact that, for each reversal
fold in the horn’s shape, a reflection is generated
inward, opposite the desired direction of wave propaga-
tion. These reverse waves are reflected again in a
forward (outgoing) direction when they reach the horn’s
driver area, generating late signal arrivals that cause
significant deviations from ideal in the horn’s response.
For this reason, folded horns generally find use in appli-
cations that are relatively undemanding of fidelity.

17.7.6.8 Special Considerations for Low-Frequency
Horns

Over the years, a number of horns have been developed
specifically to radiate low frequencies. In the past, the
primary motivation for the use of a horn to reproduce
low frequencies was improved efficiency as compared
to a direct radiator. The current availability of power
amplifiers with extremely high output capacities and
woofers that are capable of utilizing that power has
rendered the issue of efficiency less important than that
of size. As a result, there are fewer low-frequency horns
on the market today than in the past.

The most common difference between bass horns

and those intended for mid- and high-frequency use,

aside from the bass horns’ larger size, is that low-

frequency horns typically do not employ compression

drivers. Instead, a cone transducer is mounted directly

in the throat of the horn.

A potential issue in low-frequency horn design and

operation is the transitional behavior of the horn. It is

common practice to use a bass horn/driver combination

to a sufficiently low frequency that the horn is too small

to provide substantial acoustic loading in the lower

portion of the bandwidth of use. In this frequency range,

the driver must operate as a direct radiator, with corre-

spondingly lower sensitivity. Although it has been

asserted that this discrepancy, which can exceed 10 dB,

may be overcome through the use of ports, in actuality

the only means of leveling the device’s response

between the two regimes of operation is with equaliza-

tion of the input signal. Given proper equalization, a bass

horn may be used in this fashion with excellent results.

17.8 Loudspeaker Systems

Most practical loudspeakers are systems comprising

multiple transducer/radiator subsystems, each of which

radiates a portion of the audio-frequency spectrum. This

area of loudspeaker design has a major impact on a

loudspeaker’s ultimate performance, yet this portion of

the design process is frequently shortchanged. In this

section we will discuss some considerations for loud-

speaker system design and performance and provides

some illustrative examples.

The desirability of dividing the audible frequency

range into multiple bands is taken for granted in most

loudspeaker applications. The most compelling reasons

for dividing the spectrum among multiple components

are:

1. By itself, the bandwidth of a practical trans-
   ducer/radiator is inadequate to meet the bandwidth
   requirements for a complete loudspeaker.


2. The directivity of a single transducer/radiator will
   not be sufficiently consistent with frequency to meet
   reasonable goals for the directivity of a full range
   loudspeaker.


3. The maximum available acoustic output of a single
   transducer is inadequate. Sharing the output demand
   among a number of band-specific components
   enables a loudspeaker to produce greater total
   acoustic power.

In designing a loudspeaker system, one should, at the

very least, have a working knowledge of the disciplines

Figure 17-40. Klipschorn folded corner bass horn—rear cut-
away view with high-frequency components. Courtesy
Klipsch & Associates.