Film-Tech Forum ARCHIVE: Headset frequencies

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Ground Level » Headset frequencies (Page 2)

This topic comprises 2 pages: 1 2

Author

Topic: Headset frequencies

Jim Cassedy
Phenomenal Film Handler

Posts: 1661
From: San Francisco, CA
Registered: Dec 2006

posted 10-14-2008 10:08 PM

quote: Frank Angel
Jim, more details please. How does this work.

Hi Frank- sorry I didn't respond sooner but it's been a couple of days since I checked this thread.

I built this thing at least 8 or 9 years ago and it was pretty rube-Goldberg, but it worked.

Here's basically what I recall doing-
1)I took an aux 'line out' of the main PA amp and fed this to a 2nd old Bogen PA amp the church had sitting around.

2) I connected the speaker output from the 2nd amp to the input of a large old audio transformer I had sitting around in my "box-o-parts" at home. The purpose of the transformer was to provide a proper load to the output of the amp.

3)I went to one of the many electronics surplus stores in Silicon Valley and picked up a roll of 5 conductor ribbon cable.
My choice of cable was mainly dictated by what I could get cheaply. I ran a loop of it around the perimiter of the church auditorium behind a baseboard that ran along the floor.
This was the most time consuming part. Where the cable crossed a doorway, I ran it under the carpeting.

4)I wired the #2-#3-#4 conductors of the ribbon cable together in series at one end (thus making the ribbon into one long electrical "loop") and then connected the two outer conducters (#1 & #5) to the audio transformer.

Voila!
When I turned the system on and tested it using an inductive loop amp usually used for tracing telephone wiring and I could clearly hear the sound.

The church did not have any headsets. Most of it's congregation were elderly and depended on using the system with inductive-compatable hearing aids. So we found one of the ministers who had a hearing aid and asked him to give it a test.

The only complaint was that the sound was sort of "bassy".
Since most older people have trouble with hi-frequency hearing loss, I simply solved this problem by turning the "bass" control all the way down on the amp and the "treble" control all the way up. If necessary, I was prepared to build a simple 'low cut' or 'hi-pass' r/c filter, but apparantly adjusting the controls did the trick.

The only other 'problem' was that if you tried to use this system and sat in the very back of the church, you picked up an electrical buzz from some old flourescent light fixtures in the vestibule on the other side of the wall.

But users of the system quickly learned just not to sit in the last row or two of the church.

| IP: Logged

Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 10-16-2008 08:11 AM

Bell Theatre Service in London makes (made?) a prepackaged loop system for sale. Louis

| IP: Logged

Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 10-20-2008 07:04 AM

Thanks, Jim. Seems simple enough, but given the size of our theatre (2500 seats) I imagine I would have to run this up and down the four isles. And are you running the output of the drive amp at 70v or 8 ohms?

And then I am not that familiar with hearing aid technology -- do most of them use induction? I mean, it would make sense that anyone who was hard of hearing and in need of hearing assistance would have hearing aids already when they walk in the theatre. So when we hand them the infrared headsets, do they have to take the hearing aid out? And would some hearing aids work on just self-contained amplification and not work with induction?

| IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1 2

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.