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
a3-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.
1.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.
2.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-
EVI-28 250-Watt Two-Way Compact Vari Intense® Speaker System
