MH4020AC Coaxial Stadium Horn System
MH4020AC Coaxial Stadium Horn System
2
rear of the front flange to aim and stabilize
the device. Electro-Voice recommends that
each MH4020AC be independently sup-
ported. The MH4020AC can be easily sus-
pended with either the 40° or the 20° cover-
age pattern horizontal. Note: the contractor-
selected high-frequency drivers contribute to
the overall weight of the MH4020AC. In
the worst case (DH2A/4MT) an additional
48 lb is added. This should be taken into
consideration when suspending the system.
Electrical connections can be made using
standard electrical boxes or weather-resis-
tant boxes if used in adverse conditions. The
mounting brackets incorporate a predrilled
flange to aid electrical box mounting.
If the MH4020AC is suspended, it is recom-
mended that the unit be inspected at least
once a year. If any sign of weakness is de-
tected, remedial action should be taken im-
mediately.
Equalization and Subpassband
Protection
The MH4020AC’s mid-bass section exhib-
its typical constant-directivity horn charac-
teristics, i.e., roll-off at the frequency ex-
tremes. At higher frequencies, the roll-off ap-
proximately matches the power-response of
the DL10X-SH (6 dB per octave). At lower
frequencies, directivity is lost when the
mouth is no longer large enough to maintain
directional control. These two consequences
can be observed in the “humped” response
in Figure 3. Equalization can be easily ap-
plied with a graphic equalizer to give a flat
response.
The high-frequency compression driver can
be equalized with a graphic equalizer or an
EQ module inserted into the Electro-Voice
XEQ-2 (two-way) or XEQ-3 (two-way or
three-way) active crossover/equalizer. The
EQ module should be selected to suit the
particular compression driver and the
HP420A horn (see relevant data sheet). Be-
cause of its use in large arenas, where air
loss can be significant, it is recommended
that the system be equalized “on site” for op-
timum results. The XEQ-3 and the mid-bass
EQ module from the EQMT-2 can be used
to provide a good starting point for the equal-
ization.
Electro-Voice strongly recommends the use
of a 100-Hz high-pass filter to protect the
drivers from unnecessary excursion and ther-
mal stress.
Connections
The four DL10X-SH drivers in the
MH4020AC horn have a nominal impedance
of 16 ohms each and can be accessed indi-
vidually and driven independently. However,
it is more typical to combine the drivers. Fig-
ure 9 illustrates some different combinations.
It is particularly important to bear in mind
the impedance of any cabling and
specifications of the amplifier before select-
ing a specific combination. Whatever the
combination selected, the polarity of the driv-
ers must be considered (see Figure 9 and
Polarity of the DL10X-SH Drivers section).
Directivity
The axial directivity factor R
θ
of the
MH4020AC was computed at each of the
one-third-octave center frequencies over the
frequency range noted from the horizontal/
vertical polars shown in Figure 7. Directiv-
ity index (D
i
) was taken over the same fre-
quency range.
Beamwidth
Plots of the MH4020AC’s 6-dB-down total
included beamwidth angles are shown in Fig-
ure 6 for each of the one-third-octave center
frequencies noted.
Polar Response
The directional characteristics of the
MH4020AC were obtained by selecting the
horizontal and vertical details from a full set
of polar data measured in EV’s large
anechoic chamber. The measurement micro-
phone was placed 6.1 m (20 ft) from the cen-
ter of rotation of the horn which, in turn, was
0.94 m (3.08 ft) behind the mouth of the horn.
See Figure 8.
Polarity of the DL10X-SH Drivers
For Manifold Technology
®
to operate cor-
rectly, the drivers must be operated “in
phase.” In other words, for parallel connec-
tion, the DL10X-SH’s must be connected so
the negative terminals of the drivers are con-
nected together, and the positive terminals
are connected together.
Service
In the unlikely event the MH4020AC re-
quires service, each DL10X-SH easily can
be replaced or serviced by removing the back
cover and then removing the driver. A ser-
vice data sheet is available from Electro-
Voice.
Power Handling Capacity
To our knowledge, Electro-Voice was the
first U.S. manufacturer to develop and pub-
lish a power test closely related to real-life
conditions. A random-noise input signal is
used because it contains many frequencies
simultaneously, just like real voice or instru-
ment program. The signal contains more
energy at extremely high and low frequen-
cies than typical actual program, adding an
extra margin of reliability. The test combines
not only the overall “long-term average” or
“continuous” level—which our ears interpret
as loudness—but also short-duration peaks
which are many times higher than average,
just like actual program. The long-term av-
erage level stresses the speaker thermally
(heat). The instantaneous peaks test mechani-
cal reliability (cone excursion). Note that the
sine-wave test signals sometimes used have
a much less demanding peak value relative
to their average level. In actual use, long-
term average levels exist from several sec-
onds on up. The test performed lasts for eight
hours, adding another extra level of confi-
dence.
Specifically, the MH4020AC mid-band sec-
tion is designed to withstand the power test
described in EIA Standard RS-426A. The
EIA test spectrum is applied for eight hours.
The spectrum is obtained by filtering white
noise (a particular type of random noise with
equal energy per bandwidth). The filter ap-
plies 6-dB-per-octave slopes below 40 Hz
and above 318 Hz. When measured with a
one-third-octave constant-percentage ana-
lyzer, this 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
