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Author Topic: Hearing Loop - What interference to test for?  (Read 885 times)

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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