Specifications

9-4
9.2 Operation with Cat. No. 580 Microphone Multiplexer
The Cat. No. 580 Microphone Multiplexer has been designed to work with, as well
as be controlled from the CP500. The multiplexer ensures more accurate theater
speaker equalization by enabling the simultaneous use of as many as four
microphones (supplied) placed throughout the auditorium. Although the unit is
normally furnished with Dolby recommended miniature measurement microphones,
it will accommodate 12V phantom powered professional microphones as well.
The multiplexer rapidly switches between the four microphones and sends their
outputs to the CP500 over the special 31-meter (100-ft.) Dolby Cat. No. 582
input/output cable (supplied). Then, the digital circuitry within the CP500 averages
the microphone outputs for display on its built-in real time analyzer and subsequent
EQ adjustments. This eliminates the time-consuming process of moving a single
microphone to different locations and manually averaging the results.
Four high-quality electret microphones are supplied with the Cat. No. 580, in
addition to six meter (20-ft.) connecting cables that adapt the microphones' standard
XLR connectors to the “mini-XLR” style input connectors on the Cat. No. 580.
The Cat. No. 582 input/output cable used to connect the Cat. No. 530 to the
CP500 contains two individually shielded pairs: one for distribution of bi-
directional RS-232 control signals and the other for the multiplexed microphone
signal.
A built-in microcontroller chip is programmed to control microphone selection,
switching rate between microphones, and the Cat. No. 530 LED display. There are
no user adjustments on the Cat. No. 530 itself.
9.2.1 Operation
Position the Cat. No. 580 Multiplexer in the center of the listening area and connect
the four microphones to the multiplexer using Cat. No. 581 adapter cables. Place
each microphone in the room so that they are substantially in the reverberant field
rather than in an area that receives the most direct energy from the speakers. In
addition, avoid perfect symmetry -- that is, arrange the microphones so that they are
not, for example, arranged in a perfect square or rectangle parallel to the sides of
the room. Take care not to place any of the microphones on the central axes of the
room, as standing waves and nodes at these positions can cause measurement
errors.
The microphones should normally be mounted at the listener's head height.
However, if the seats have high backs, the microphones should be raised to have at
least 23 cm (9 inches) above the top of the seat to avoid unwanted effects.