Electro-Voice TL880D - Manual (Page 2)

TL880D Very-Low-Frequency Speaker System
TL880D Very-Low-Frequency Speaker System
Specifically, the TL880D is designed to with-
stand the power test described in ANSI/EIA
RS-426-A 1980. The EIA test spectrum is
applied for eight hours. The spectrum is ob-
tained by filtering white noise (a particular
type of random noise with equal energy per
bandwidth). The filter applies a 6-dB-per-
octave slope below 40 Hz and above 318 Hz.
When measured with a one-third-octave con-
stant-percentage analyzer, this filter produces
a spectrum whose 3-dB-down points are at
100 Hz and 1,200 Hz with a 3-dB-per-oc-
tave slope above 1,200 Hz. This shaped sig-
nal is fed to the power amplifier with the
continuous power set to provide 1,200 watts
into the 4.8-ohm EIA equivalent impedance
(75.9 volts rms).
Amplifier clipping sets instantaneous peaks
at 6 dB above the continuous power, or 4,800
watts peak (151.8 volts peak). This proce-
dure provides a rigorous test of both ther-
mal and mechanical failure modes.
The TL880D has also been power tested with
a two-hour sine wave, at minimum imped-
ance, so that competitive comparisons can
be made using consistent methods. Continu-
ous program power is defined as 3 dB above
(double) the continuous sine-wave power
rating.
Subpassband Speaker Protection
Below the enclosure tuning frequency, cone
excursion increases rapidly. Since acoustic
output is also falling rapidly, there is no util-
ity in driving the system with signals much
below tuning frequency. While such signals
may be in the program material, they are of-
ten extraneous, such as a dropped micro-
phone. The Electro-Voice EX-24, XEQ-2
and XEQ-3 electronic crossover/equalizers
can provide the necessary subpassband pro-
tection. The 3-dB-down points are 30 Hz
(EX-24 and XEQ-2) and 16 Hz or 32 Hz
(XEQ-3).
Other high-pass filters are available and one-
third-octave equalizers can also be effective
at providing the required protection.
Use In Multiples
Cone loudspeakers may be stacked for
greater acoustic output and a narrower
beamwidth. (It is assumed that all cones are
operating in unison or “in phase.”) This prin-
ciple is already employed in the dual-woofer
TL880D, and is responsible for the higher
sensitivity and narrower vertical beamwidth
(with the system long axis vertical) relative
to similar single-woofer systems. In addition,
two TL880D’s can be used side-by-side and
their combined performance will be differ-
ent from that of a single TL880D in the ways
outlined below.
At relatively low frequencies, below about
150 Hz for typical TL series dimensions,
stacking produces additional acoustic out-
put without altering dispersion. When a com-
mon signal is applied, a 6-dB increase in
maximum acoustic output occurs. The cones
“mutually couple” and act as one cone with
twice the area (therefore twice the efficiency)
and twice the power capacity. The additional
cone area provides 3 dB more output and
the 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 calcu-
lated from the following equation:
3,000
f @ ————— ,
D
MAX
where D
MAX
(inches) is the distance between
the cones, and f (Hz) is the highest frequency
at which coupling occurs. When D
MAX
is
greater than one-quarter wavelength, which
would occur if two TL880D’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.
Installation and Suspension of TL880D
Enclosures
The TL880D is designed for typical cinema
stage (behind-the-screen) applications where
subwoofers are mounted on the stage floor.
The TL880D is not designed to be self-sus-
pended from above, and if suspended,
must be supported and hung in a way
which does not depend on the structure
of the TL880D itself for support.
Architects' and Engineers'
Specifications
The loudspeaker system shall be a dual low-
frequency, bass-reflex design. Two 18-inch
woofers shall be front mounted in an 15.5-
ft 3 enclosure. The system shall meet the fol-
lowing criteria: power handling, 1,200 watts
of pink noise with a 6-dB crest factor; fre-
quency response, smooth and uniform, us-
able at high output levels from 23 to 2,000
Hz; sensitivity, 98 dB at one watt, one meter,
100 to 800 Hz, on axis; impedance (woofers
paralleled), 4 ohms nominal, 4.2 ohms mini-
mum; dispersion angles 220° (horizontal) x
180° (vertical) at 200 Hz. The enclosure
shall be constructed of black texture-painted
poplar plywood . The enclosure will contain
sound-absorbing glass wool. Each woofer
shall have the capacity to be fed indepen-
dently of the other. The input panel and con-
nectors shall be side-mounted. An installed
vent cover shall be supplied that, when re-
moved, shall raise the box tuning frequency
from 25 Hz to 30 Hz, for increased output in
the 30- to 40-Hz range. The enclosure di-
mensions shall be 47.5 in. high x 30.0 in.
wide x 23.8 in. deep (121 cm x 76.2 cm x
60.5 cm). Net weight shall be 160 lb (72.6 kg).
The low-frequency speaker system shall be
the Electro-Voice TL880D.
Uniform 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.
Exclusions 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