Electro-Voice TL880D ユーザーズマニュアル

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.

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.

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.

The TL880D is designed for typical cinema

stage (behind-the-screen) applications where

subwoofers are mounted on the stage floor.

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.

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