Theatre Design & Technology - Summer 1983 - 8

Figure 3: Piezoe{ecfric High-Frequency Driver

Figure 4: Cone Loudspeaker-direcf radiafor

PERMA>ENT MAGNET --H'---",;=ffi

VOCE COL

llIAPtRAGM

~Ht-t--+---THlOAT

-t+-----?t

2x5 MUlT1CELLHORN

RADIAL HORN

Figure 5: Compression Driver

Although cones as large as 30" diameter have been made, a cone for use
at low bass frequencies is usually 15" or
18 ". Often more than one driver is required for high-level music reproduction. Cones of 10" or 12" diameter can
do a good job with low bass notes at
home listening levels. Those smaller
than I0" are rarely expected to produce
a useful low bass.
While loudness in the low-frequency
range is mechanically limited, loudness
at all frequencies is limited by the ability to dissipate the heat created by large
currents flowing through the fine wires
of the voice coil. Most failures in cone
loudspeakers are burnouts, and most
could be prevented by paying attention
to the early warning signal-awful distortion caused by banging at the mechanical limits.
Another limiting factor is the ability
of the cone to move exactly with the
voice coil. This is a particularly vexing
problem with larger cones that have
been especially fabricated to move large
6

amounts of air at low frequencies. This
construction is not very compatible with
the need for reproducing the very short
fast vibrations of high frequencies.
Most 15" and 18" cones start to break
up around I000 hertz. The cone begins
to add spurious vibrations when it attempts to follow the voice coil at higher
frequencies. This generation of distortion limits the usefulness of the large
cone driver at higher frequencies.
The rule in high-quality, high-level
reproduction is to divide the sound spectrum among two or more drivers which
are sized and optimized to limited
ranges. A cone driver is always used for
the bass range up to 500 to 800 Hz.
Sometimes a cone driver may be used in
the mid range up to 2000 to 5000 Hz.
Small cones can be used at high frequencies when high sound levels are not required or when the cone is coupled to a
horn for added efficiency. In most large
room applications, however, cone loudspeakers are rarely satisfactory for
tweeters; compression drivers are al-

Theatre Design & Technology /USITT /Summer 1983

Figure 6: Horns

most always used for high-level, highfrequency reproduction.
Compression Driver (Fig. 5)
The magnetic action of a compression driver is identical to that of the cone
driver, but the acoustical action is quite
different. While the moving cone creates sound pressure waves directly, the
thin metal diaphragm of the compression driver acts to compress a volume of
air in a pressure chamber. This chamber
is vented to the outside by a narrow
throat leading into a horn-type radiator.
It is the horn that couples the varying
pressures in the throat to the air of the
room. The compression driver is able to
overcome many of the high-frequency
break-up problems of the cone driver.
Modern compression drivers are able to
operate to the upper limits of hearing at
very high sound pressure levels with acceptable distortion.
A compression driver is subject to
the same mechanical and thermallimitations as the cone driver. However, the



Table of Contents for the Digital Edition of Theatre Design & Technology - Summer 1983

Contents
Theatre Design & Technology - Summer 1983 - 1
Theatre Design & Technology - Summer 1983 - 2
Theatre Design & Technology - Summer 1983 - 3
Theatre Design & Technology - Summer 1983 - Contents
Theatre Design & Technology - Summer 1983 - 5
Theatre Design & Technology - Summer 1983 - 6
Theatre Design & Technology - Summer 1983 - 7
Theatre Design & Technology - Summer 1983 - 8
Theatre Design & Technology - Summer 1983 - 9
Theatre Design & Technology - Summer 1983 - 10
Theatre Design & Technology - Summer 1983 - 11
Theatre Design & Technology - Summer 1983 - 12
Theatre Design & Technology - Summer 1983 - 13
Theatre Design & Technology - Summer 1983 - 14
Theatre Design & Technology - Summer 1983 - 15
Theatre Design & Technology - Summer 1983 - 16
Theatre Design & Technology - Summer 1983 - 17
Theatre Design & Technology - Summer 1983 - 18
Theatre Design & Technology - Summer 1983 - 19
Theatre Design & Technology - Summer 1983 - 20
Theatre Design & Technology - Summer 1983 - 21
Theatre Design & Technology - Summer 1983 - 22
Theatre Design & Technology - Summer 1983 - 23
Theatre Design & Technology - Summer 1983 - 24
Theatre Design & Technology - Summer 1983 - 25
Theatre Design & Technology - Summer 1983 - 26
Theatre Design & Technology - Summer 1983 - 27
Theatre Design & Technology - Summer 1983 - 28
Theatre Design & Technology - Summer 1983 - 29
Theatre Design & Technology - Summer 1983 - 30
Theatre Design & Technology - Summer 1983 - 31
Theatre Design & Technology - Summer 1983 - 32
Theatre Design & Technology - Summer 1983 - 33
Theatre Design & Technology - Summer 1983 - 34
Theatre Design & Technology - Summer 1983 - 35
Theatre Design & Technology - Summer 1983 - 36
Theatre Design & Technology - Summer 1983 - 37
Theatre Design & Technology - Summer 1983 - 38
Theatre Design & Technology - Summer 1983 - 39
Theatre Design & Technology - Summer 1983 - 40
Theatre Design & Technology - Summer 1983 - 41
Theatre Design & Technology - Summer 1983 - 42
Theatre Design & Technology - Summer 1983 - 43
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https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Oct
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https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965May
https://www.nxtbookmedia.com