User manual

1220 controller front view
GR LO
ISP
GR HI
OV LO
OV HI
CUT
MON
LFC
MUTE
1220-CO
0
+3-3
0
-6
-12
-18
dB HI dB
ID
(4.0 E) 3-1
3. Controller modules
The different controller modules include all the signal processing
electronics, front panel controls and indicators needed to control
and operate a specific matching active loudspeaker system. Shown
opposite is the 1220-CO used with the F1220 and M1220 loud-
speakers. The actual controller circuitry, controls, indicators and
rear panel connectors will of course vary depending upon the re-
quirements of the loudspeaker design they are intended to drive
3.1. Features
Input circuit
A balanced and band-limited input circuit protects the system
against out-of-band signals and radio frequency interference.
Equalisation
Equalisers in the controller module match the relative levels of the
high and low drivers used in full range cabinets and ensure the
linear frequency response of the loudspeaker system. Some
controller modules are fitted with additional configuration switches
to give the user a degree of control over the system frequency
response.
Highpass filter
A highpass filter circuit fine tunes the bass-reflex loudspeaker
enclosures used in these systems and also helps to maintain a linear
low frequency response while protecting the loudspeakers from
extreme sub bass signals.
Subwoofer crossover filters
The controller modules for the subwoofer systems incorporate a
lowpass filter as an active crossover to a full range/TOP system.
Conversely, the full range systems have a switchable highpass filter
for use with an additional subwoofer system.
Thermal limiter
An internal control circuit simulates the loudspeaker voice coil tem-
peratures under actual load conditions. The output of this circuit is
used to protect drivers by reducing the signal level when critical
temperature values are reached.
LF displacement limiter
A second internal control circuit simulates the mechanical displace-
ment of the LF driver cone and reduces the signal level before
overexcursion damage can occur.
Clipping limiter
To maintain sound quality output stage clipping is kept within
reasonable bounds by a limiter circuit. The limiter threshold alters
to take account of the supply voltage to the mainframe power
amplifiers. So if the mains supply voltage or the connected load
impedance alter, then the limiter automatically tracks these changes
to maintain the system sound quality.
2-way active crossover
The controller modules for the full range 1220 and F2 systems
employ active crossover circuits to split the controller input signal
into high & low signal paths to separately feed the high & low