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Author
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Topic: Infrared hearing system signal tap help
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Rick Long
Jedi Master Film Handler
Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999
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posted 03-07-2003 10:10 PM
We recently installed the infared Phonic Ear system in a ten-plex.
The equipment; 8 cinemas with CP-65's 2 cinemas with CP-45's. All cinemas have Component Enginering MS-100 monitors. All cinemas using Ashely FTX-1501 bi-amped amplifiers for stage channels.
Experiments showed a substantially higher signal from the "MONO OUT" terminal on the monitor than from the "H/I" terminal on the processors, hence we used this terminal.
The MS-100 uses a resistor summing network from the L LE C RE and R channels consitsting of 5 100K resistors. As has been mentioned earlier, they do not include the surround channels as the delayed surround would make the sound rather "muddy".
We found also, that the gain in the hearing impared system had to be sufficient to overcome the sound from the screen. As this would be delayed by the time for the sound travelling from the screen to the listening position combining with instanteaneous sound from the headphones, this would also provide a delay, again making the sound "muddy".
Despite the superior signal level of the MS-100, there was not enough gain to over-ride the sound from the screen. To compensate for this, we reduced the gain controls on the back of the screen amps (we use L,C,R here only) from its former position of zero to -6.
Of course, the signal levels on the processors had to be raised to obtain 85dbC slow in the auditorium, but this gave us the gain we needed from the monitors.
The CP-45's however, provided us with a special problem. They have a lower gain than the 65's, thus we were not able to drop the amp input controls that low.
To make a long story short, we opened the monitors in these two cases and dropped the L C and R 100K resistors to 47 K. Results were good with no discernable loss of separation.
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