Film-Tech Forum ARCHIVE: Hearing Assist -- FM vs IR

This is topic Hearing Assist -- FM vs IR in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Angel (Member # 248) on 03-19-2010, 05:15 PM:

We need to reinstall a Hearing Assist system in our large house. Problem with the original IR system was that it had tons of dead-spots, even though ugly IR transmitters were placed around the walls, the coverage lacked uniformity. To compound the problem, it is a slope floor, not a stadium in the orchestra so the receiver could easily be blocked by the person sitting in front, especially when cloats and such are hung on the seats.

This time we are looking into an FM type system as well. It would seem that these are much easier to install (simple antenna mounting in only one place and they claim 3000ft coverage) and no problem with line-of-sight issues. On the other hand, it is RF and with that can come some pretty serious transmission interference. However, my understanding is that since the FCC reallocated radio frequencies for specific commercial useage, the cross traffic stepping on each other is much less of a problem these days.

Does anyone have any experience with an FM being used theatrically? Anyone know of theatres that use the RF type instead of IR and what do you think of it. We would like to be able to talk to an end-user to hear their practical experience with such a system.

I am thinking there must be a reason why so many use IR as opposed to RF, but as far as simplicity goes, the FM transmission seems to win hands down, not to mention that it is much cheaper that IR in terms of installation. That 3000ft coverage figure seems a bit high to me and any time a manufacture claims transmission distance, I always figure halving that number would probably be more accurate. Still 1500ft would be more than enough for what we need.

Here is one of the systems are looking at: ListenTech FM Hearing Assist System

Thanks for any ideas about this.

Posted by Monte L Fullmer (Member # 2797) on 03-19-2010, 07:37 PM:

Check into the Sennheiser units. They have one radiator that can really fill a large area.

the USL IR units are real good as well. Large spaces needs only two emitters.

Tricks with large areas is to have the IR emitters above and in front of the audience in the corners of the room angling down to the center of the room.

Or, two emitters mounted high and center of the room with each emitter angling down and out to the middle edge of the room.

FM can get into probs with the simple case of multiple receivers assigned on the required frequency along with those milliwatt transmitters broadcasting where they want to along with drifting issues.

I've dealt with the Gertner FM units and even though they're not too bad, but issues with receivers having to use regular headphones and the maintenance issue in this spectrum, whereas the IR self contained receiver units - just replacing the batteries is the only maintanence needed.

Good Luck - Monte

Posted by John Hawkinson (Member # 1135) on 03-19-2010, 07:51 PM:

I would do a site survey on the frequencies you're considering. You never know what the noise floor is like, and in Brooklyn you're more likely to have random interference than many other places.

--jhawk

Posted by Louis Bornwasser (Member # 3063) on 03-19-2010, 11:11 PM:

FM is great for 1 or 2 screens. You must not mix the receivers.

IR works for multiplexes; any receiver will work in any room. The kiddos who hand out receivers can't screw up. Louis

Posted by Sam D. Chavez (Member # 1841) on 03-20-2010, 10:36 AM:

The reason the USL units work so well is the headphones are purpose built for movies and the receiver is on top of the headphone and less likely to be shaded by hats, coats, etc.

Posted by Demetris Thoupis (Member # 833) on 03-20-2010, 11:04 AM:

IR based Hearing Assist or Translation systems (basically the same thing) can pickup interference from Fluorescent light as well as plasma emmition (this is not your case) I found during my installs that placing two emmiters (one on top left and other on top right) of a room are the best way to go and you have complete coverage. Judging from the USL line and experience in cinema applications I recon their system would be the best solution. I had a situation of a theater where the RF receivers of the wireless microphones were picking up nearby taxi service!!
Demetris

Posted by Gordon McLeod (Member # 33) on 03-20-2010, 01:04 PM:

One issue with IR systems is interference from Daylight or CFL light fixtures

Posted by Jeremy Weigel (Member # 4208) on 03-20-2010, 01:22 PM:

We been using Williams Sound transmitters/receivers and haven't had too many problems. Every once in a while we used to pick up a nearby tv station audio. [Confused]

Haven't noticed it since the switch to digital.

Posted by Bob Peticolas (Member # 328) on 03-20-2010, 01:49 PM:

We have used both Nady and Telex FM systems with no problems. With the transmitter just sitting on top of the audio rack, the theatre is covered plus about 1/2 block out side of the theatre. I would not use the 72-76 mhz systems, too much interference. Go with the 216 mhz or higher systems, their range isn't a great thus the interference is less. With an antenna just outside the booth window, your auditorium will be covered up to 300 or so feet.

Plugging a receiver into a small amplifier or PA system gives you a monitor that can be place anywhere to listen to the theatre's sound with no wiring. Ideal for lobby sound or special events outside of the theatre itself.