CX261 Installation and User Guide v1.5
15
Music EQ
Treble and bass equalisation for the music signal is provided via
rear panel pre-set
MUSIC EQ
controls ([3] at “Description
of rear panel” on page 9
). This allows the installer to tailor
the response of the Zone Mixer’s music channels to suit the
acoustics and loudspeakers in each zone. The EQ controls are
marked
HF
and
LF
; the HF control has a range of +/-10 dB
at 10 kHz and the LF control a range of +/-10 dB at 50 Hz.
A flat frequency response is achieved by positioning the slots
on the controls in the horizontal plane.
Note that the
MUSIC EQ
controls do not affect the music
signal at the MOH/Auxiliary output.
Music Limiter
The music channel of the CX261 incorporates a limiter
circuit to help prevent inadvertent overloading of subsequent
power amplifier input stages and ultimately, the installed
loudspeakers. The limiter has no external controls. If the
music input gain and level controls are set correctly, the
limiter action should be inaudible on normal programme
material, with no compression artefacts.
The threshold of the music limiter is factory set at 0 dBu,
thus signal peaks above this level will be limited. A higher
threshold of +6 dBu can be set by moving internal jumper
J15 (see “PCB jumper location and settings” on page 20
for jumper location); this will give improved fidelity, and may
be appropriate if the installer is confident about the dynamic
range of the programme material.
If there is dynamics control elsewhere in the system
(e.g., in the form of an external compressor/limiter or within a
DSP-based unit), or if limiting is considered undesirable,
the limiter may be by-passed by removing J15 from the
PCB header.
Microphone Inputs
Phantom Power
Each microphone input has 12 V phantom power available.
This will be adequate to power a wide range of condenser
microphones. (Some “studio quality” mics may require a
higher phantom voltage and thus necessitate an external
PSU.) To enable phantom power at the mic inputs, the internal
PCB jumpers J1 (Mic 1) and/or J2 (Mic 2) should be moved to
their ON positions. See “PCB jumper location and settings”
on page 20 for jumper locations.
Phantom power should NOT be enabled if dynamic
microphones are to be used.
Gain & level
Each microphone input is provided with a rear panel preset
GAIN
control ([6] at page 9
). A wide range of gain is
available (10 to 50 dB), and there should be no problem in
obtaining a satisfactory level from any normal microphone.
Immediately below each
GAIN
control is a bi-colour (green/
red) LED ([8] at
page 9
) which monitors input signal level.
These can be used to adjust the
GAIN
preset. During an
announcement made in a normal speaking voice, adjust the
GAIN control so that the LED (for the mic input in use)
illuminates green fairly steadily. An occasional red flash is
acceptable, but If red shows persistently, turn the
GAIN
control down slightly. Note that a signal level of -24 dBu is
required to trigger the green LED while a level of 0 dBu will
initiate limiter action (see “Microphone Limiter” on page
16
), which may have an audible effect on audio quality.
In normal operation, the mic level in each zone is set with the
MIC 1 LEVEL
and
MIC 2 LEVEL
controls on the front
panel ([8] & [9] on “Description of front panel” on page 8
).
EQ
Two-band equalisation adjustment is provided for the
microphone signals: note that these affect both
MIC 1
and
MIC 2
inputs. The
MICS EQ
pre-set controls are on the rear
panel ([7] at “Description of front panel” on page 8
). The
equalisation is optimised for the tonal correction of speech
signals: the
HF
control provides +/-10 dB at 5 kHz whilst
the
LF control pr/10 dB at 100 Hz. A flat frequency
response is achieved by positioning the slots on the controls
in the horizontal plane.
High Pass Filter
Each mic input has a fixed 100 Hz high-pass filter to remove
the lowest frequencies. This helps to reduce the effects of
breath blasts and microphone handling noise. The filter is
always in circuit.
