Speaker system – Electro-Voice EVI-28 User Manual

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EVI-28 250-Watt Two-Way Compact Vari Intense

Speaker System

EVI-28 250-

att T

-W

ay Compact V

ari Intense

Speaker System

term average level stresses the speaker

thermally (heat). The instantaneous peaks

test mechanical reliability (cone and dia-

phragm excursion). The sine-wave test sig-

nals sometimes used have a much less de-

manding peak value relative to their aver-

age level, providing a much higher power

handling specification than is appropriate

for real-world use. In actual use, long-term

average levels exist from several seconds

on up, but we apply the long-term average

for eight hours, adding another measure

of reliability. Additional extremely high-

stress tests developed in-house push com-

ponents to the limits to ensure long-term

reliability under the most extreme cases of

abuse.

Specifically, the EVI-28 is designed to with-

stand the power test described in ANSI/

EIA RS-426-A 1980. The EIA test spec-

trum is applied for eight hours. To obtain

the spectrum, the output of a white-noise

generator (white noise is a particular type

of random noise with equal energy per

bandwidth in Hz) is fed to a shaping filter

with 6-dB-per-octave slopes below 40 Hz

and above 318 Hz. When measured with

the usual constant-percentage bandwidth

analyzer (one-third-octave), this shaping

filter produces a spectrum whose 3-dB-

down points are at 100 Hz and 1,200 Hz with

a 3-dB-per-octave slope above 1,200 Hz.

This shaped signal is sent to the power am-

plifier with the continuous power set at

250 watts into the 6.9-ohm EIA equivalent

impedance. Amplifier clipping sets instan-

taneous peaks at 6 dB above the continu-

ous power, or 1000 watts peak. The EVI-28

has been thoroughly tested at an AES

equivalent power level of 350 watts con-

tinuous for 2 hours with 1,400 watt peaks.

This procedure provides a rigorous test of

both thermal and mechanical failure modes.

Amplifier Power Recommendations

As noted in the Power-Handling Capacity

section above, the EVI-28 has a random-

noise power capacity of 250-watts long

term (1000-watts peak) per ANSI/EIA

RS-426-A 1980. The following guide-

lines will help relate this number to an ap-

propriate power amplifier output rating.

To use the EVI-28 to full capacity,

skilled experts in sound-system instal-

lation and operation will obtain the

best results if the power amplifier is

2.0 to 4.0 times the long-term average

noise power rating of the speaker

system. For the EVI-28, this is 500

to 1000 watts.

The caution cannot be made strongly

enough, however, that this arrangement

is only for experts or for those who can

discipline themselves against “pushing”

the system for ever-higher sound levels

and who can avoid “accidents” such as

catastrophic feedback or dropped micro-

phones.

A more conservative, “normal” ampli-

fier size, which will produce audible

results nearly equal to those of the

“expert” recommendation, is 1.0 to 1.4

times the long-term average noise

power rating of the speaker. For the

EVI-28, this is 250 to 350 watts.

3. To be very conservative, one can use

an amplifier rated at 0.5 to 0.7 times

the long-term average noise power

rating of the loudspeaker. For the EVI-

28, this is 125 to 175 watts.

Request P.A. Bible Addition No. Two

(“Power Handling Capacity”) for more

background on these recommendations.

EVI-28 Connections

Electrical connections to the system are

made by large screw terminals able to ac-

cept up to 10-gauge wire, mounted to an

input panel on the back of the enclosure.

Speaker Protection

The EVI-28 like all other vented systems

experiences rapidly increasing cone excur-

sion below the box tuning frequency, while

the acoustic output decreases rapidly. To

ensure a long woofer life even when used

at high power levels, it is recommended

that some form of electronics be used to

control unnecessary woofer cone excur-

sion.

Graphic equalizers and active crossovers

are two methods that can be used to pre-

vent low-frequency signal below band-

pass from going to the loudspeaker. When

using and active crossover, a high-pass

filter with a cut-off frequency of 35- to 50-Hz

will provide the necessary protection. The

filter should have a slope of at least 12 dB

per octave. Such subpass band filters are

found in many crossovers and equalizers

manufactured by Electro-Voice, as well as

other commercially available equipment.

Enclosure Construction and Refinishing

The enclosure is constructed from high-

grade void-free 12-mm (0.5-inch) 9-ply and

18-mm (0.71-inch) thick 13-ply birch ply-

wood and lined with sound-absorbent cot-

ton batting. This high-strength enclosure

is coated with an attractive textured black

or white finish for a truly professional ap-

pearance. Systems with unfinished enclo-

sures suitable for staining come with a black

grille and may be ordered for a small addi-

tional charge. The included 3/8-16 hang-

ing points ensure easy installation in nearly

every application. The grille is constructed

from a sturdy 16-gauge medium-gloss black

or white powder-coated steel and may be

painted or covered with cloth to match the

enclosure. If the grille is painted, the acous-

tic foam insert should be removed during

painting and reattached with a contact or

spray adhesive on the grille, such as 3M

Super 77. Take extreme care to replace the

foam insert in its original position and pre-

vent paint or adhesive from covering the

foam, as it will obstruct the pores and de-

grade the performance of the system.

Suspending EVI-28 Enclosures

WARNING: Suspending any object is po-

tentially dangerous and should only be at-

tempted by individuals who have a thor-

ough knowledge of the techniques and

regulations of rigging objects overhead.

Electro-Voice strongly recommends that

the EVI-28 be suspended taking into ac-

count all current national, federal, state

and local regulations. It is the installer’s

responsibility to ensure that the speaker

system has been safely installed in accor-

dance with all such regulations. Electro-

Voice strongly recommends that all sus-