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Author Topic: Hearing Loop - What interference to test for?  (Read 887 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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Philip Roberts

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Re: Hearing Loop - What interference to test for?
« Reply #10 on: February 01, 2019, 05:27:11 pm »

Thanks for all the input, I've been reading along but haven't had time to respond.

- We have an existing 72MHz Telex ALS system that we plan to continue to use. We do have some neck loops for this but I'm sure that the user with t-coils would prefer not having to check out a device every week. Switching to 216 MHz would be nice but I don't think I can make the case that it's worth the price.
- I haven't had time to watch the video from Univox yet. I'll make sure and check which type of system is planned. I'm afraid the plan is a series of PLS style loops, one for each seating zones. I think they are doing multiple zones based on the loop area each amp channel can drive.

Further questions:
For those of you who've used loop systems with guitars and such has the problem generally been feed back if the guitar is routed to the loop of does the loop signal get injected into the guitar pickup enough to "contaminate" it with the rest of mix sent to the loop so that the signal sent to the loop is audible when cuing the guitar?

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.

Simon, not sure I understand what this test you describe would show. Is it not safe to assume that most loop amps have gotten their grounding and input topology right?

Thanks

Philip
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Simon Lewis

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Re: Hearing Loop - What interference to test for?
« Reply #11 on: February 04, 2019, 09:08:48 am »

Hi, Philip,

There are instances where having the desk and loop amp on different parts of a mains circuit can give rise to an earth condition where there is a magnetic feedback loop. It's not too common, and possibly arises due to the different way UK mains tends to have final circuits wired.

The purpose of feeding a signal direct to the loop amp it to determine whether the loop is breaking into the audio rig when there is no electrical connection between the two at all - i.e. it is purely an induced interference.

With regards to interference on guitars, the worst case scenario is that there is a feedback loop setup up between the magnetic signal and the audio circuit which gives rise to audible feedback. Usually, taking the guitar out of the loop mix will help to reduce this, but making sure the magnetic loop field doesn't reach the guitar in the first place is usually a better approach...

Simon




.
Thanks for all the input, I've been reading along but haven't had time to respond.

- We have an existing 72MHz Telex ALS system that we plan to continue to use. We do have some neck loops for this but I'm sure that the user with t-coils would prefer not having to check out a device every week. Switching to 216 MHz would be nice but I don't think I can make the case that it's worth the price.
- I haven't had time to watch the video from Univox yet. I'll make sure and check which type of system is planned. I'm afraid the plan is a series of PLS style loops, one for each seating zones. I think they are doing multiple zones based on the loop area each amp channel can drive.

Further questions:
For those of you who've used loop systems with guitars and such has the problem generally been feed back if the guitar is routed to the loop of does the loop signal get injected into the guitar pickup enough to "contaminate" it with the rest of mix sent to the loop so that the signal sent to the loop is audible when cuing the guitar?

Simon, not sure I understand what this test you describe would show. Is it not safe to assume that most loop amps have gotten their grounding and input topology right?

Thanks

Philip
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Steve Anderson

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Hearing Loop - What interference to test for?
« Reply #12 on: February 10, 2019, 04:11:40 pm »

I'm afraid the plan is a series of PLS style loops, one for each seating zones. I think they are doing multiple zones based on the loop area each amp channel can drive.
Hi Philip,
Be very careful about a design like this.
If you have multiple seating areas separated by typical aisle widths, you almost certainly wonít get even coverage with the loop system.
Careful consideration to the polarity of each loop may go some way to curtailing the uneven coverage, but wonít fix the issue completely.
Also, how big is each area? And what is the floor made from? [You may have mentioned earlier, but I canít see earlier posts while posting from my phone]
Steve
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Philip Roberts

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Re: Hearing Loop - What interference to test for?
« Reply #13 on: February 11, 2019, 04:20:34 pm »

Hi Philip,
Be very careful about a design like this.
If you have multiple seating areas separated by typical aisle widths, you almost certainly wonít get even coverage with the loop system.
Careful consideration to the polarity of each loop may go some way to curtailing the uneven coverage, but wonít fix the issue completely.
Also, how big is each area? And what is the floor made from? [You may have mentioned earlier, but I canít see earlier posts while posting from my phone]
Steve
Is there some sort of modeling program analogous to EASE for modeling the coverage of hearing loops so I can ask for reports showing the predicted coverage?

We have a test/demo schedule for tomorrow so I should know more then. We have 8 seating areas, each ~12-14' wide (along a pew) x 60-80' (rows of pew). The plan might be to combine two horizontally adjacent sections, I'm not really clear at this point. Floor is ~1960 concrete, no solid steel pan but there are some steel rods/mesh/rebar inside, we don't know exactly what/were. I think it was cast in place but I don't know for certain.

Philip
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Simon Lewis

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Re: Hearing Loop - What interference to test for?
« Reply #14 on: February 12, 2019, 03:37:31 am »

Philip,

Not sure if the modelling programmes are so readily available outside the manufacturer/installer user base, but your provider ought to have access to one. I'd be surprised if a multi loop array hadn't been modelled.
As an example, I've attached a prediction I had done for me by the UK manufacturer Ampetronic..

Simon


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