Dolby Laboratories CP65 manual Appendix a Checking Phasing of Speakers

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A.1

APPENDIX A

CHECKING PHASING OF SPEAKERS

Loudspeakers are two-wire devices that can be connected incorrectly as well as correctly. Incorrectly wired loudspeakers in a multiple-speaker installation cause degraded performance. For example, woofers in an array must work together to generate a solid wavefront of sound pressure. If some woofers are moving in one direction at the same time that other woofers are moving in the opposite direction, the result is partial cancellation and hence loss of bass. (The lower the frequencies being handled, the greater is the cancellation.) Wiring can be reversed inside a connector, a transformer can be mislabeled, and the internal wiring polarities of mixers, crossovers, voice coils, and other inaccessible equipment may be unknown.

The Cat. No. 85C pink noise generator can be used to determine correct speaker phasing. Position a microphone as shown on page 5.7 and connect it to the RTA. Switch on pink noise to the center channel in phase (C switch down) and observe the RTA display. Switch on pink noise to the left channel in phase (L switch down). The level in each band displayed on the RTA should rise by 2 to 4 dB. If the level in any band decreases then check phasing of the speaker connections. Repeat this procedure for center and right channel speakers.

IN PHASE

OFF

OUT OF PHASE

A number of hand-held devices are available to assist the installer to determine if the speakers in a theatre installation are correctly wired. Virtually all such devices consist of two units — a pulse or tone generator which is connected to the speaker being tested — and a polarity detector which is driven either by an integral or external microphone. The detector contains LEDs which indicate the direction of motion of the speaker. It is necessary only to connect the generator to the speaker being tested and turn on the test signal. The detector LEDs automatically indicate the direction of motion. It is sometimes difficult to interpret the indication given on these devices, but they are useful in determining whether several loudspeakers behave identically. (If a special adapter cable is made, the generator can be connected to the CP65 aux input or the L and R output test points on the Cat. No. 240 module so the phase check will include all of the system after the optical preamplifier.)

It is strongly recommended that the phasing of all of the speakers be checked before any of the alignment procedures are started.

Typical phasing checkers are as follows:

SCV Audio Model PC80-439 available from QMI, 15 Strathmore Road, Natick, MA 01760

Cricket Polarity Test Set available from Galaxy Audio, 625 E. Pawne, Wichita, KS 67211

Check with your dealer for complete information on these and other systems.

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Contents Model CP65 Cinema Processor Dolby Laboratories Inc Headquarters Table of Contents Section Reference Block Diagrams Introduction Page Section Equipment Required Jiffy Test Film Cat. No 2 Listen . . . Film Cat. No Smpte Buzz Track Stereo Optical Surround Level Cat. NoSection Initial SET-UP and Installation Voltage Acceptable Setting Voltage Range Fuse Type Next, check the jumpers in the following locations Cat. No , B-Chain Card Cat. No , Power Supply ModuleJ2 NON-SYNC Cat. No , Control Logic CardStandard CP65 or CP65A CP65 BackplaneCP65-300 High Low Subwoofer subwoofer Output output These Modules are Necessary for Bypass Operation Two-channel Noise Slot Card Function Cat. NoReduction Module Channel DecoderContains a semi-regulated power supply with International Voltage Setting Fuse TypeIEC Notices Room lighting dimmer controls SCR-TYPE HUM ProblemsPage Aligning the B-Chain Section AN Overview of the Alignment ProcedurePage Page Section Chain Alignment Action Indication Preliminary ProceduresLamp Voltage Optical Preamplifier Adjustments Chain Alignment Procedures Optical Preamplifier Adjustments 222 CAT. no Test Film Oscilloscope Traces Repeat Repeat 1 → CAT noMagnetic Preamplifier Adjustments Magnetic Alignment 100mV Section Chain Alignment Bypass Setting Room EqualizationLoudspeakers and Crossovers General AmplifiersOff Chain Alignment ProceduresAction RepeatChain Alignment Procedures Setting Room Equalization Do not adjust Paul 14 → 21 R 14 → Setting Room Equalization b. Adjusting L,C,R Gain79 dBC Setting Mono GainChain Alignment Procedures Subwoofer Alignment Cat. No 85 dBC 90 dBCStep No FromSelect format 04 Dolby Stereo A-Type 441 Same ASSurround Equalization Alignment Cat. No Cat. No 441 Surround Equalization Alignment Cat. No NotesDesired 88 dBC Bypass Msec Setting Adjustment of Surround DelayThumbwheel Switch Xx dBC Chain Alignment Procedures Adjustment of Bypass GainXx dBC -3 dB Yy dBC FromPress the format 60 non sync switch Adjustment of Non-sync GainAuto Freq Repeat page 5-20 Step Adjustment of Mono Gain and Equalization NotesPress the format 04 Dolby Stereo A-type switch Chain Alignment Procedures Final ChecksSection Reference Diagrams Cat. No Dual Noise Reduction Module Inputs Cat. No Optical Bass Extension and Surround Equalizer Card Cat. No B-Chain Facilities Card Cat. No Power Supply Card Cat. No Transformer Module Inputs Cat. No Control Logic Card +15M Cat. No +24V +15V15V +12B Appendix a Checking Phasing of Speakers Appendix B Effect of Changes in Slit Height on Slit Losses Cat. No a Circuit Description Appendix C CP65M Mono InstructionsOperation Schematic Cat. No a Terminal Block TB3 Appendix D Backplane Connections ListConnector J18
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