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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 excursion.
Graphic equalizers and active crossovers are
two methods that can be used to prevent low-
frequency signal below band-pass from going
to the loudspeaker. When using an active cross-
over, a high-pass filter with a cutoff frequency
of 32- to 45-Hz will provide the necessary pro-
tection. 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
The Sx500PI+ enclosure is contructed of very
durable structural foam that is hard to dent,
scratch or break. The structural foam enclosure
allows for the high- and low-frequency horns,
the stand mount and the suspension points to
be molded into the enclosure. It also allows for
three handles to be integrated into the enclo-
sure.
Frequency Response
The combination of a 15-inch woofer, wide-
bandwith high-frequency driver and an equal-
ized crossover results in the wide and smooth
overall response shown in Figures 1a and 1b.
Figure 1a is the response with the ports open
while Figure 1b is the response with the two
optional port plugs installed. This response was
measured at 3.05 meters (10 feet), using a 4-
volt swept sine-wave input in an anechoic
chamber using the internal passive crossover.
No external equalization was used. Figures 1a
and 1b have been averaged and corrected for 1
watt at 1 meter.
Port Plugs
The two ports, on either side of the high-fre-
quency horn, may be "sealed" in order to add
further weather protection to the system. These
optional foam port plugs are included with the
system for use in situations where increased
weather resistance is needed. This will help
prevent any moisture from wicking through the
foam-backed grille and accumulating inside the
enclosure under extreme weather condidtions.
The optional port plugs and instructions are
supplied with each system. It should be noted,
however, that once the port plugs are installed,
2
the frequency response will change to that
shown in Figure 1b.
Connections and Biamping
The Sx500PI+ is equipped with two parallel
®
Neutrik Speakon
NL4MP connectors. In the
full-range mode, as supplied by the factory, pins
1+ and 1– are the inputs to the system.
Another system can be connected in parallel
by using the other connector. Care must be
taken not to abuse the amplifier by connecting
impedances which are too low.
The user may put the system in biamp mode
by removing the input panel and moving a con-
nector from the full-range mode to biamp mode,
as noted on the crossover. In biamp mode, 1+,
1– are the LF inputs and 2+, 2– are the HF
inputs.
Constant-Directivity Speaker System
The crossover frequency and speaker- compo-
nent geometries have been selected so that the
directional characteristics of the woofer and
constant-directivity high-frequency horn match
at the crossover frequency to create a special
system type — the constant-directivity system.
At higher frequencies, the horizontal coverage
pattern remains constant and the vertical pat-
tern smoothly transitions to a 60° angle above
5,000 Hz. Response within the 75° x 60° rated
coverage angle is uniform, which means de-
pendable audience coverage without "hot
spots" or dead zones at certain frequencies. The
75° x 60° dispersion characteristic also helps
avoid early reflections from nearby floor or
side-wall surfaces which could degrade perfor-
mance. The controlled directivity of the high-
and low-frequency transducers also eliminates
response irregularities caused by diffraction off
nearby enclosure edges and, in combination
with an essentially flat on-axis frequency re-
sponse, produces a total acoustic power output
that is uniform with frequency.
Directivity
A unique feature of the Sx500PI+ is the con-
stant-directivity dispersion provided by the 75°
x 60° horn. The polar response of the system
at selected one-third-octave bandwidths is
shown in Figure 2. These polar responses were
measured in an anechoic environment at 6.1
meters (20 feet) using one-third-octave pink-
noise inputs. The frequencies selected are fully
representative of the polar response of the sys-
tem. Beamwidth of the system utilizing the
complete one-third-octave polar data is shown
in Figure 3. Directivity factor, R
ity index, D
, are plotted in Figure 4.
i
Power-Handling Capacity
The Sx500PI+ is shipped in full-range mode
using an internal crossover. In biamp mode, the
long-term average power-handling capacity is
as follows:
Low Frequency: 400 watts
High Frequency: 60 watts
Electro-Voice components and systems are
manufactured to exacting standards, ensuring
they will hold up, not only through the most
rigorous of power tests, but also through con-
tinued use in arduous, real-life conditions. The
EIA Loudspeaker Power Rating Full Range
(ANSI/EIA RS-426-A 1980) uses a noise spec-
trum which mimics typical music and tests the
thermal and mechanical capabilities of the com-
ponents. Electro-Voice will support relevant ad-
ditional standards as and when they become
available. Extreme, in-house power tests, which
push the performance boundaries of the woof-
ers, are also performed and passed to ensure
years of trouble-free service.
Specifically, the Sx500PI+ passes ANSI/EIA
RS-426-A 1980 with the following values:
R = 5.76 ohms (1.15 x (R
E
R
= woofer DCR
E
1.86 =horn-load impedance correction
P
= 400 watts
E(MAX)
Test voltage = 48.00 volts rms,
96.00 volts peak (+6 dB)
The "peak" power-handling capacity of a
woofer is determined by the peak test-voltage
amount. For the Sx500PI+, a 96.00-volt peak
test-voltage translates into 1,600-watts short-
term peak power-handling capacity. This is the
equivalent of four times the "average" power-
handling capacity, and is a peak that can be
sustained for only a few milliseconds. How-
ever, this sort of short duration peak is very
typical in speech and music. Provided the am-
plifier can reproduce the signal accurately with-
out clipping, the woofer will also perform ac-
curately and reliably, even at these levels.
Amplifier Power Recommendations
As noted in the Power-Handling Capacity section
above, the Sx500PI+ has a random-noise power ca-
pacity of 400-watts long term (1,600- watts peak)
per ANSI/EIA RS-426-A 1980. The following
guidelines will help relate this to an appropriate
power amplifier output rating.
and directiv-
,
+ 1.86))
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