Film-Tech Forum ARCHIVE: Infrared hearing system signal tap help

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Posted by Andy Muirhead (Member # 712) on 03-07-2003, 04:28 PM:

We are installing an Infrared Hearing System into one of our screens. At the moment we are trying to figure out the best place to tap the audio from.

This screen has an Ultra-Stereo processor, model JS-100

One line of thought is taking the stereo signal from the pre-amp out l-r on the back of the processor.

Anybody have any ideas?

Another idea is to tap into the L/C/R/S between the processor and the booth monitor.

Any help and words of wisdom would be much appreciated!

The make and model of the infrared system is the SoundPlus Infrared System, Model WIR TX925

Posted by Jack Ondracek (Member # 1466) on 03-07-2003, 04:49 PM:

Our H/I systems connect to a mono output from our booth monitor. You might check to see if yours offers this feature. Our processors also have an output specifically for an H/I system.

Check both your processor and booth monitor for H/I or "mono" summed outputs. If you don't have one anywhere in your system already, then it's time to consider other options.

Posted by Andy Muirhead (Member # 712) on 03-07-2003, 06:13 PM:

We have checked both the booth monitor and processor for those outputs hence the need to try and find some other way of tapping a decent signal!

Although there may well be something around the back of the Ultra-Stereo that is similar to your suggestion and we haven't spotted it yet.

Posted by Phil Hill (Member # 371) on 03-07-2003, 06:21 PM:

I've used a RS "Stick-On" mixer to combine the LCR screen channels at line level feeding the booth monitor.

>>> Phil

Posted by Darryl Spicer (Member # 711) on 03-07-2003, 08:37 PM:

on ours we tapped off the center and left channel speaker outputs on the amps. But you could probably achieve the same results tapping off the monitor amp inputs. It's a mono souce anyways so I do not see a need to use all the channel outputs Just the L/C/R for digital. To much could cause distortion in the sound.

Posted by Gerard S. Cohen (Member # 994) on 03-07-2003, 08:53 PM:

While I can't help wirh your question directly, I agree with Darryl that the surround channels aren't needed. For people with hearing problems, the center dialog channel is what's important.
Effects channels can cause confusion and pain to those with defective hearing. I know using hearing aids, sounds outside the speech frequency and dynamic range become distorted, and I imagine the boost of a theatre system would prove similar.

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-07-2003, 09:04 PM:

That's the one advantage of mixes without directional dialogue -- the C/Hi output will be sufficient for your hearing impaired system.

If there isn't an output designed for a hearing impaired system on the JS-100 or your booth monitor I would connect to the C/Hi output at the processor itself. Don't forget to connect the shield at the processor and lift it at the Hearing Impared System (or whatever gives you clean audio w/o ground loops [Smile]

).

Connecting there shouldn't noticably effect your center channel level but you might want to check it after just in case.

Posted by Rick Long (Member # 213) on 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.

Posted by Joe Morris (Member # 1553) on 03-08-2003, 12:01 AM:

I had a Ultra Stereo j 100 DON'T tap into the pre-amp inputs on the back. If you tap from anywhere not there. you will cause the sound in your auditorium to drop dramatically. tap it from the monitor or from the center output. that should allow your patrons to adjust the volume on their headsets accordingly as well as allow you to have full sound in your auditorium

Posted by Brad Miller (Member # 2) on 03-08-2003, 12:11 AM:

Just a note, if you have digital sound of some sort, do NOT tap off of the center channel only. You will find lots of music and crucial parts of the soundtrack will be absent to your hearing impaired customers.

I couldn't agree with Daryl more about not tapping off of the surrounds.

Posted by Peter Hall (Member # 695) on 03-08-2003, 08:36 AM:

A lot of IR transmitters we use (Williams incl) have a cut off cct, to shit the thing down when not in use. Typically this will be around 150mV. Can be a prob when using high gain amps and the CPxx output - we suggest using a resistor matrix (10k on each line, 10 k across) to sum the L C R SPEAKER outputs - this way it's irrespective of high amp gains (= low processor outputs) and doesn't introduce any xtalk. Or, yes, use a high quality monitor (shameless plug - like the FP8-bi model with a high level (700mv) HI outpur) with a HI out (doing virtually the same thing).

Posted by Peter Hall (Member # 695) on 03-08-2003, 08:38 AM:

Meant to say SHUT, not SHIT ! Oh shut, screwed up .. Lifes a bag of shut.. (Kiwi prouncuation for shit)

Going for some fush and chups now..