Dolby Laboratories CP650 Installation Manual download pdf (Page 113)

Dolby

Model CP650 Installation Manual Final Adjustments

7-17

7.14.4 “FAIL” Parameters

Noise Floor

A failure is indicated if a new auditorium noise floor measurement differs from the

saved reference measurement by more than ±10 dB. The measurement is taken at a

bandwidth between 20 Hz and 16 kHz.

The noise level in the auditorium is an important part of any theatre environment.

This test is designed to measure the room noise, and to determine if it has changed

significantly. The CP650 mutes, and a comparison is made between the noise

received by the microphone and the stored reference reading. If this comparison fails,

the following message is inserted into the event log:

“Aud Noise xx dBr”

Where xx dB is the number of decibels over or under the stored reference noise

reading. If the auditorium noise is more than ±10 dB from the reference level, then

the frequency tests do not occur.

Level and Frequency Response

A failure is indicated if a new frequency response measurement of any channel (L, C,

R, Ls, Rs, Bsl, or Bsr) differs from the saved reference measurements by more than

±3 dB. The measurement is taken in the region between 200 Hz and 5 kHz.

A failure is indicated in the subwoofer channel if the frequency response deviates by

more than ±5 dB from the reference reading, in the region between 60 and 100 Hz. A

change in the sound level from a speaker can be caused by many factors, including:

• Power amplifier gain has been changed, or the amplifier has failed

• Crossover has been changed or has failed

• Speaker has been changed, has failed, an element has an open circuit, etc.

If the comparison fails any of the frequency response/level tests, a message is inserted

into the event log. For example:

“R FAIL MH”

The “R” indicates the Right channel. An “L,” “M,” or “H” represents low-, mid-, and

high-frequency regions. L frequencies are below 315 Hz, M frequencies are between

315 Hz and 2 kHz, and H frequencies are above 2 kHz. If more than one channel

failed the test, multiple events are added to the event log.

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Dolby Laboratories CP650 Installation Manual Page 113