5. Stacking Guidelines
The sound designer must know if the audience is standing or seat-
ed, but the bottom of the cluster should - in any case - be higher
than the heads of the first rows of the audience and the lowest ele-
ment tilted downwards.
If the cluster is too low, the first rows receive too much SPL and
audience members directly in front of the system act as an acoustic
screen for the rows behind them (
shadowing
). Ideally, the MF-HF
speakers should be slightly above the audience (not lower than 2
m or 6.5 ft above floor level), with a proper volume regulation as
necessary.
Note: for extended bandwidth applications, a stack of 2 XTHPS33
subwoofers, in horizontal position, provides a convenient stacking
platform at a height of 1.2 m above ground level.
6. Subwoofers
Subwoofers are used to extend the frequency response of the stand-
ard system (XTH+XTL) up to to 25-30 Hz and to increase the overall
SPL without increasing the potential for audience hearing loss.
7. General Guidelines for the use of subwoofers
The number of subwoofers to be used depends on 3 parameters:
1) Number of XTH-XTL elements
. The standard number of XTS
subwoofers recommended is a
1:1
ratio.
2) Type of program material.
Standard subwoofer ratios are rec-
ommended for classical music or for background music. For these
applications, subwoofers act as a low frequency extension for
XTH+XTL system and provide approximately 6 dB of low frequency
contour. In this case, the overall system functions as an extended
bandwidth 4-way system in tri-amplification. For more demanding
rock music applications, a ratio of
1:2
(1 XTH+XTL - 1 XTS) is recom-
mended to provide a more suitable low frequency contour).
3) Type of venue or installation.
In open-air, when subs are
ground stacked, the quantity remains standard.
8. Amplification
X-Treme Classic Line speakers are designed to be used with profes-
sional power amplifiers capable of producing the following outputs
into 8 Ohm:
XTH: 550 W
XTL: 850 W
XTS: 1200 W
and into 4 Ohm:
XTLT: 460 W
Care should be taken to avoid amplifier clipping. It is important to
understand that a low power amplifier driven into clipping is more
likely to damage a loudspeaker then a higher power amplifier used
within its ratings. This is because music signals have a high peak-
to-average factor. When an amplifier is severally overdriven, its out-
put waveform is clipped (its peaks are squared off) – reducing the
crest factor. In extreme cases, the waveform can approach that of
a square wave. Furthermore, an amplifier normally consumes far
more electric power under these conditions than its undistorted rat-
ed power output. The use of very high power amplifiers with output
greater than those recommended is discouraged.
Care should be taken to avoid switch-on surges, which can result in
momentary power peaks in excess of specified ratings.
When powering up a sound system it is important
to switch on the
amplifiers after the electric supply of the mixer and control electron-
ics have stabilised
. When powering down the system, reverse the
sequence and switch off the amplifiers first.
9. Connectors
The rear panel of Classic Line loudspeaker systems are fitted with
two Neutrik Speakon NL4 connectors. All four pins of both connec-
tors are wired in parallel. The XTH and XTLT uses pin assignments
2+/2-. Pins 1+/1- are designed to XTL and XTS. Using the male con-
nector as the input, the female connector allows for direct connec-
tion to additional speakers (link or bridge connection).
PINS
1+
1-
2+
2-
NL4
LF+
(XTL)
(XTS)
LF-
(XTL)
(XTS)
HF+
(XTH)
(XTLT)
HF-
(XTH)
(XTLT)
4 pins Speakon connector:
1+: Positive (+) woofer - XTL, XTS
1-: Negative (-) woofer - XTL, XTS
2+: Positive (+) satellite - XTH, XTLT
2-: Negative (-) satellite - XTH, XTLT
10. Cable length
When connecting loudspeaker systems to an amplifier, it is recom-
mended that the return resistance of the cable used is less than
one
tenth
of the nominal impedance of the system or systems in parallel.
The table below gives an indication of the maximum permissible
cable runs for various conductor cross-sectional areas.
Maximum Cable Run
Conductor CSA
4 ohm
8 ohm
1.0 mm
2
11 m
22 m
1.5 mm
2
17 m
34 m
2.0 mm
2
22 m
44 m
2.5 mm
2
29 m
58 m
4.0 mm
2
44 m
88 m
6.0 mm
2
66 m
132 m
11. System configurations
X-Treme Classic Line enclosures can be used with analog control-
lers which perform system specific equalization, crossover and lim-
iter functions. More complex set-ups will benefit from the use of a
digital DSP - X-Treme Classic systems can be used with
XTDP26
Digital Speaker Management
or any other professional digital con-
troller. Whichever controller is used, it is important that it has fast
attack limiters to prevent amplifiers from clipping. This requires that
the controller’s limiter thresholds be set to match the sensitivity of
the amplifier. A system operated in this way - with amplifiers having
a power rating as recommended and used by experienced profes-
sional sound engineers - should be sufficiently protected from over-
driving. It is suggested that you refer to the controller user’s guide for
further information on how to set limiter thresholds.
The nominal horizontal coverage pattern of XTH is
60-degrees
. This
has been found to be the optimum figure to meet the requirements
of both small scale and larger scale use.
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