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additional power capacity accounts for the
remaining 3 dB.
Specifically, mutual coupling occurs at fre-
quencies whose wavelengths are longer than
one-quarter the center-to-center distance
between the cones. The highest frequency at
which mutual coupling occurs is calculated
from the following equation:
3,000
f @ ————— ,
D
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where D
(inches) is the distance between
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the cones, and f (Hz) is the highest frequency
at which coupling occurs. When D
greater than one-quarter wavelength, which
would occur if two TL550D's were widely
spaced, or at frequencies much above f even
when closely spaced, the increase in acous-
tic output is limited to the 3-dB power-han-
dling increase.
At frequencies above the mutual coupling
limit, f, stacking alters dispersion and in-
creases on-axis sensitivity. In the 500-to-800-
Hz range, a common crossover frequency for
two-way sound reinforcement systems, two
nearly adjacent cones have a coverage angle
about half that of either cone alone. This is
useful, for example, in more closely match-
ing the typical 40° vertical dispersion of a
high-frequency horn. (At frequencies much
above 800 Hz, the concept of a halved cov-
erage angle no longer applies, since the side
lobes, which result from two sources that are
not mutually coupled, increase in number and
approach or equal the main lobe in ampli-
tude. The number of lobes and their ampli-
tude increases as frequency increases.)
HIGH-FREQUENCY HORN MOUNTING
The optional HMK-1 and HMK-2 horn
mounting kits are available for use, respec-
tively, with the Electro-Voice HP940 small-
format and HP9040 large-format constant-
directivity horns. The kits are designed to
facilitate fixing and aiming the high-fre-
quency horn and driver on top of a vertically
oriented TL550D, in cinema stage (behind-
the-screen) applications. This configuration
may be useful in a number of other applica-
tions as well. Refer to the individual HMK-
1 and HMK-2 engineering data sheets for
details and instructions.
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TL550D Low-Frequency Speaker System
Installation and Suspension of TL550D
Enclosure
The TL550D is designed for typical cinema
stage (behind-the-screen) applications where
low-frequency systems are mounted on plat-
forms, behind the screen and some distance
above the stage floor. The TL550D is not
designed to be self-suspended, and if sus-
pended, must be supported and hung in a
way which does not depend on the struc-
ture of the TL550D itself for support.
The HS6 and HS7 kits allow the TL550D to
be hung safely in a variety of orientations.
is
The combination of the correct HS kits and
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TL550D enclosure has been certified by an
independent structural engineer to be safe
and secure. Each HS kit consists of a steel
tube, two brackets, two eyebolts and the nec-
essary fasteners. The installer must assemble
the HS kit by first drilling two holes into the
TL550D enclosure, in predefined positions,
and then screwing the brackets onto the steel
tube, which passes through the enclosure. An
eyebolt is inserted in the T-nut in the rear
panel of the enclosure to provide a "pull up"
to aim the enclosure. Full instructions and
hole locations are included with each cabi-
net and HS kit. A TL550D requires a single
HS6 to suspend it horizontally, or a single
HS7 to suspend it vertically. Electro-Voice
recommends that only one TL550D be sus-
pended at one time in this manner. Vertical
is defined as having the long side vertical.
Full attention must be given to the instruc-
tions and limitations in the HS kit instruc-
tion sheet.
Architects' and Engineers'
Specifications
The loudspeaker system shall be a dual low-
frequency, bass-reflex design. Two 15-inch
woofers shall be front mounted in an 8.4-ft
enclosure. The system shall meet the follow-
ing criteria: power handling, 1,200 watts of
pink noise with a 6-dB crest factor; frequency
response, smooth and uniform, usable at high
output levels from 40 to 2,000 Hz; sensitiv-
ity, 100 dB at one watt, one meter, 100-800
Hz, on axis; impedance 4 ohms nominal, 4.2
ohms minimum; dispersion angles 120°
(horizontal) x 55° (vertical) at 500 Hz. The
enclosure shall be constructed of black vi-
nyl-clad particle board. The enclosure will
contain sound-absorbing glass wool. Each
woofer shall have the capacity to be fed in-
dependently of the other. The input panel and
connectors shall be side-mounted. The en-
closure top panel shall be fitted with T-nuts
that accept the optional Electro-Voice HMK-
1 and HMK-2 horn mounting kits. A port
cover shall be included to enable "step-
down" operation for enhanced low-fre-
quency performance. The enclosure dimen-
sions shall be 39.5 in. high x 22.5 in. wide x
21.8 in. deep (100.3 cm x 57.2 cm x 55.4
cm). Net weight shall be 144 lb (65.5 kg).
The low-frequency speaker system shall be
the Electro-Voice TL550D.
Limited Warranty
Electro-Voice products are guaranteed
against malfunction due to defects in mate-
rials or workmanship for a specified period,
as noted in the individual product-line
statement(s) below, or in the individual prod-
uct data sheet or owner's manual, beginning
with the date of original purchase. If such
malfunction occurs during the specified pe-
riod, the product will be repaired or replaced
(at our option) without charge. The product
will be returned to the customer prepaid. Ex-
clusions and Limitations: The Limited
Warranty does not apply to: (a) exterior fin-
ish or appearance; (b) certain specific items
described in the individual product-line
statement(s) below, or in the individual prod-
uct data sheet or owner's manual; (c) mal-
function resulting from use or operation of
the product other than as specified in the
product data sheet or owner's manual; (d)
malfunction resulting from misuse or abuse
of the product; or (e) malfunction occurring
at any time after repairs have been made to
3
the product by anyone other than Electro-
Voice Service or any of its authorized ser-
vice representatives. Obtaining Warranty
Service: To obtain warranty service, a cus-
tomer must deliver the product, prepaid, to
Electro-Voice Service or any of its autho-
rized service representatives together with
proof of purchase of the product in the form
of a bill of sale or receipted invoice. A list of
authorized service representatives is avail-
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