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Author Topic: Hearing Loop - What interference to test for?  (Read 721 times)

Philip Roberts

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Hearing Loop - What interference to test for?
« on: January 29, 2019, 10:52:00 pm »

My church is in the late planning process for a sanctuary renovation where it's pretty much decided we will be adding a hearing loop system.

I believe it will be a multi-loop installation but I've not actually seen a design yet. For this to work effectivly for hearing impaired users what sorts of things should I be looking at as we review the loop system design?

Wanting to make sure that before installation we understand  the likely sources of interference into our AV systems are so we can mitigate them. Most audio is Dante, we run a full multicamera video system, so have lots of SDI and other digital video system, relatively few analog video signals are still in use. We do still have analog CATV for lobby feed's etc.

As I understand it the biggest source is single coil (non-humbucking) pickup in electric or bass guitars. What other system (acoustic guitars, audio, video, cable TV, intercom, ....) have you ever noticed problems with? Other than keeping the instruments well out side the loop(s) what if anything can be done to reduce how much they pickup? How have you work around any other problems you've found?

Thanks

Philip
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Erik Jerde

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Re: Hearing Loop - What interference to test for?
« Reply #1 on: January 30, 2019, 01:45:07 am »

We worked around it by using standard 72Mhz system from Listen Tech.  No interference problems.  Proper antenna placement serves our 1100 seat room just fine.  No worries about a hard to fix coil getting damaged or interference with pickups.
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Justice C. Bigler

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Re: Hearing Loop - What interference to test for?
« Reply #2 on: January 30, 2019, 03:11:36 am »

I hope you are also installing the proper IR or RF based assisted listening systems also. Even though the hearing aid lobby likes to present induction loops as the be all, end all of assisted listening systems; the reality is that only a small percentage of people who have hearing problems have hearing aids. And of them, only about 15-20% of hearing aid users have hearing aids with tele-coils installed, and even then a significant portion of those users will forget to turn their t-coils on and still complain about the system not working. So you still are required by law to have systems that will service the majority of users.

ADA requirements require that an induction loop service be provided for those users who have the t-coils installed in their hearing aids. It DOES NOT require that you install a full room induction loop. You can satisfy the legal requirements by using the personal lanyard style induction loops as used by Listen Technologies and Williams Sound, which Erik mentioned above.
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Justice C. Bigler
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Johan Liderud

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Re: Hearing Loop - What interference to test for?
« Reply #3 on: January 30, 2019, 03:15:07 am »

My church is in the late planning process for a sanctuary renovation where it's pretty much decided we will be adding a hearing loop system.

I believe it will be a multi-loop installation but I've not actually seen a design yet. For this to work effectivly for hearing impaired users what sorts of things should I be looking at as we review the loop system design?

Wanting to make sure that before installation we understand  the likely sources of interference into our AV systems are so we can mitigate them. Most audio is Dante, we run a full multicamera video system, so have lots of SDI and other digital video system, relatively few analog video signals are still in use. We do still have analog CATV for lobby feed's etc.

As I understand it the biggest source is single coil (non-humbucking) pickup in electric or bass guitars. What other system (acoustic guitars, audio, video, cable TV, intercom, ....) have you ever noticed problems with? Other than keeping the instruments well out side the loop(s) what if anything can be done to reduce how much they pickup? How have you work around any other problems you've found?

Thanks

Philip


There are two  different type of loops for hearing aid recivers PLS and SLS.
PLS is cheaper to install but have lot of spill outside of the covered area.
SLS requires more installation  but the spill outside of the covered area will be much less with less problem for instruments with pickups like bass and guitars.

If instruments with electrical pickups are used, make sure that a SLS type system is installed and only to cover the seating area with some distance to the performer.

Include a link to a short presentation.
https://youtu.be/WgaPxSX8S8I

Difference of SLS and PLS
http://www.goteneljud.se/Teleslingor.htm

Take contact with these http://www.nhtsales.com/


Regards
Johan




« Last Edit: January 30, 2019, 09:11:32 am by Johan Liderud »
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Scott Helmke

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Re: Hearing Loop - What interference to test for?
« Reply #4 on: January 30, 2019, 09:07:09 am »

To clear up what sounds like some confusion over guitar pickups and interference...

It's the guitar pickups that will suffer. The loop is transmitting, which can be picked up by some guitar/bass pickups.
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Mike Caldwell

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Re: Hearing Loop - What interference to test for?
« Reply #5 on: January 30, 2019, 10:49:10 am »

If you go with an RF system in addition to or instead of the loop system get a Listen Technologies 216mhz band band system. The cost is the same any they work much better than the 72 or 75 mhz band systems.

Erik Jerde

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Re: Hearing Loop - What interference to test for?
« Reply #6 on: January 30, 2019, 12:42:56 pm »

If you go with an RF system in addition to or instead of the loop system get a Listen Technologies 216mhz band band system. The cost is the same any they work much better than the 72 or 75 mhz band systems.

How are they better?
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Russell Ault

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Re: Hearing Loop - What interference to test for?
« Reply #7 on: January 30, 2019, 02:58:32 pm »

I hope you are also installing the proper IR or RF based assisted listening systems also.

As an alternative, instead of running two separate assisted listening systems, you can buy T-coil receivers to give to patrons that don't have t-coil-enabled hearing aids. One of the venues I work at did this after a recent renovation (replacing an IR system) and the system seems to work well.

(Incidentally, the system that was installed was a multi-loop system for controlled coverage that doesn't seem to have caused an interference problems on the stage, although I seem to recall us having to turn the system off when the SM moved to an in-house production table because their SM58 VOG mic would pick up the feed...)

-Russ
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Mike Caldwell

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Re: Hearing Loop - What interference to test for?
« Reply #8 on: January 30, 2019, 05:18:40 pm »

How are they better?

Better coverage / range and they sound better as in less background noise.
As a bonus the antenna is a lot smaller.

Simon Lewis

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Re: Hearing Loop - What interference to test for?
« Reply #9 on: February 01, 2019, 03:36:03 am »

Philip,

The discussion here has covered many of the pros and cons of the available assisted listening systems. As the US has a slightly different regulatory system from the UK and a likely smaller user base of hearing aids fitted with telecoils, I'll refrain from commenting on the "best" system except to say that all have some inherent drawback.

To answer your query, at the design stage the loop array should be calculated for a) even coverage of the intended area and b) - if possible - designed with a cancellation turn towards the stage, to help minimise spill in that direction.

The typical instances of interference include:
Hum bars on video displays due to interference on analogue (VGA) video cabling (solution - use digital!)
Pickup of loop signal by poorly screened DI boxes (solution - use decent DI boxes)
Pickup of loop signal by single coil guitar pickups (solution - use humbucker pickups, use cancellation type loop, turn guitarist 90 degrees)
Pickup of loop signal in some cabling or instrument amplifiers on stage (solution - use cancellation type loop, ensure that there isn't a ground loop between the audio amp and the induction loop amp).

If your church does have a loops system fitted, keep the cabling etc. connected to the loop amp but then try adding a signal source directly to the loop amp and see if that signal can be heard anywhere in the audio system. If it can, then try disconnecting the cable between the desk and loop amp to check if that is part of the problem.

I would normally create a separate ALS mix which heavily promotes vocals and speech, and has little music content. If there are problematic instruments (guitars with single coil pickups etc.) it can be better to leave them out of the ALS mix.

Induction loops aren't perfect, but they do certain offer benefits not usually available with IR and FM systems.
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