Dolby Laboratories CP750, Manual

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44 Dolby
®
CP750 Digital Cinema Processor Manual
Aligning the Auditorium
6.1.2 Amplifiers
• Check for distortion.
• Check for gross gain differences among amplifiers. If one amplifier differs in
performance from the others, it should be checked and repaired.
• Check for blown fuses.
• Ensure that there is good air movement through power amplifiers.
• Check any air filters.
6.1.3 Air Conditioning
If air ‐ conditioning noise is audible in the theatre, minimize it by:
• Lubricating the motor and fan bearings
• Adjusting belts and drives
• Cleaning the filters or screens on the air ‐ conditioning returns
6.2 Microphone Placement
Position a microphone multiplexer in the center of the auditorium listening area. Place each
microphone in the reverberant field rather than in an area that receives the most direct
energy from the speakers. In addition, avoid perfect symmetry. Arrange the microphones
so that they do not form a square or rectangle parallel to the sides of the room. Take care
not to place any of the multiplexing microphones on the auditorium center line. Standing
waves and nodes can cause measurement errors.
During final SPL calibration, microphone number 1 should be placed two ‐ thirds of the
distance from the front speakers to the rear, at the exact side ‐ to ‐ side center of the room,
approximately five feet above the floor level, and rotated 45 degrees upward toward the
screen. (Some multiplexer microphones are designed to be pointed directly at the ceiling.)
Placement of this microphone is important for output level adjustments.
Figure 6 ‐ 1
Figure 6-1 Microphone Placement for Equalization
If a single microphone is used, which we do not recommend, use the number 1 position
detailed above, but place it slightly off center during equalization.