Induction Loop interference

[Ynot]

It's been a long time since we've had a loop system in my venue for those with hearing aids (T-pickups) but we recently had a guy contact us who's been to a few shows and was asking why we didn't. The answer was simple - we'd not had anyone in the past 20 years say that they were having trouble hearing the action on stage, and as a medium sized amateur venue seating just 250 on a raked auditorium that isn't a massive surprise.

However, he told us that when he'd been to shows lately he counted maybe 1 in 4 punters had some sort of hearing aid (that does sound a little high if I'm honest) but he said that he and his also hard of hearing friend WERE struggling at times to hear what was going on.

He then brought in a rack-mounted loop amplifier he'd borrowed for us to have a trial with. From memory it is a Signet AVX PDA1000 older model.

 

We did a very rough experiment with running a simple 1.5mm single insulated wire from the amp in the booth around the floor of the auditorium and back. This gave him actually a very good pickup on his hearing aid, so an initial success. So we discussed options for running it under the seating, where we can, but that as a short term measure was going to be a bit time consuming - and as we have a show in this week it wasn't going to happen immediately.

We then tried a large loop coming out of the booth and around the back auditorium wall, so this loop was at 90 degrees to the floor - this surprisingly gave him a good pickup for about 6 or 7 rows from the back, and as that was a less intrusive and simpler way of doing a temporary job we left that in as the chap was due in for opening night on Tuesday.

 

However, we did notice that using either of the loop paths we did pick up the signal being sent to the loop as a low inductive signal on both of the control room amps, including the one over the LX desk. Whilst not a huge surprise - after all, we'd just created a large aerial transmitting RF - I was surprised how clear it was, even in the background.

 

So - the question is - how can we isolate that signal from being picked up? Different cable? Some sort of screening? If so how/where?

 

Cheers

[Shez]

The layout of the loop is key. You* can create a low spill layout that will minimise the signal strength in areas that you don't want it. It's very rare that a simple, single loop of wire is optimum.

 

*It's a bit of a specialist job - Ampetronic did the last one I needed. Signal strength drops like a stone where we didn't want it.

[Simon Lewis]

Tony,

 

The perimeter loop should ideally be in the plane of the listener, rather than at 90 degrees to it. You will most likely have quite a strong field strength above, below and to the sides of the loop on the back wall, but not a very even one going into the seating area.

If you are getting pickup around the amps in the tech area, check that the loop cables from where they meet together to where they are connected to the loop amp are twisted together. This reduces radiation in the immediate vicinity.

 

There aren't simple means of "screening" but if the "feeder" cable is twisted and the loop is in the correct orientation, it is usually manageable. It's possible to install a cancellation (unequal figure of eight ) loop but suspect that may not be easily achieved with existing raked seating.

Ultimately, whilst getting a loop to work (especially if the temporary arrangement - however flawed) does seem good, you might want to consider one of the "lower cost" infra red systems.

 

Loops still remains the aid user's preference, because they can simply switch to it without any additional equipment. However loops do have a variety of interference, spill and metal loss issues - some of which can be overcome by design and clever techniques.

IR and FM radio are a good technologies but do require hardware for each user to be bought, maintained, charged up and booked out (and back in again!).

Voice over Ethernet through the user's mobile phone appears a brilliant idea, and can work extremely well, but it does also present a number of technical and even social challenges.

 

Hope you can reduce the bleed you're experiencing... let us know how you get on!

 

Simon

[Ynot]

Thanks - will give those ideas a punt.

Infra red may be worthy going forward but at the moment this is nil cost whilst we have this loaner amp... Will maybe look at alternatives going forward.

There are probably grants available for improving accessibility if I can find time to investigate...

 

TD

[sunray]

I usually find any interference is due to 2 reasons:

1/ the tail from the loop is not twisted/not twisted tight enough, or

2/ unbalanced cables in the audio system.

My experience of IR systems is poor, all too often the RX is hanging round the users neck and in a shadow from the row of seats in front, the batteries need to be managed properly, and 2 RX close to each other (2 users sitting side by side) interfere.

 

[gyro_gearloose]

Our Sennheiser infrared system allows users to connect earphones to the receivers if they wish, so they don’t need to have a hearing aid of their own. Also, if you go for a two channel system you can use it for audio description for visually impaired customers.

[Robin D]

You may find a lump of foil lined board attached to earth on the loop side of the amps etc provides enough of a Faraday screen.

[Owain]

The local council's induction loops for its confidential interview rooms were all clearly receivable in the shopping centre at the back of the building

[Simon Lewis]

Our Sennheiser infrared system allows users to connect earphones to the receivers if they wish, so they don't need to have a hearing aid of their own. Also, if you go for a two channel system you can use it for audio description for visually impaired customers.

 

Similarly, you can get loop receivers with headphone outputs..... but loops cannot (easily) provide a two channel system.

 

You may find a lump of foil lined board attached to earth on the loop side of the amps etc provides enough of a Faraday screen.

 

Sadly, that approach tends to do little to stop the magnetic field...

[Ynot]

Twisting the wires at the amp to where they split has apparently made a big difference, so thanks for that pointer.

[Simon Lewis]

Twisting the wires at the amp to where they split has apparently made a big difference, so thanks for that pointer.

 

Excellent...! If only every "loop installer" would do as you have done...! ;-)

[sunray]

You may find a lump of foil lined board attached to earth on the loop side of the amps etc provides enough of a Faraday screen.

That won't make the slightest bit of difference

 

The local council's induction loops for its confidential interview rooms were all clearly receivable in the shopping centre at the back of the building

We installed a loop in a board room, designed by Ampertronic for zero spill from the room. Sadly it was detectable in the corridor, my solution was a loop in said corridor connected to a half wave rectified supply with just enough current to defeat the loop.

 

The local council's induction loops for its confidential interview rooms were all clearly receivable in the shopping centre at the back of the building

We installed a loop in a board room, designed by Ampertronic for zero spill from the room. Sadly it was detectable in the corridor, my solution was a loop in said corridor connected to a half wave rectified supply with just enough current to defeat the loop.

 

Twisting the wires at the amp to where they split has apparently made a big difference, so thanks for that pointer.

 

Excellent...! If only every "loop installer" would do as you have done...! ;-)

I second that

 

Twisting the wires at the amp to where they split has apparently made a big difference, so thanks for that pointer.

 

Excellent...! If only every "loop installer" would do as you have done...! ;-)

I second that

 

Our Sennheiser infrared system allows users to connect earphones to the receivers if they wish, so they don’t need to have a hearing aid of their own. Also, if you go for a two channel system you can use it for audio description for visually impaired customers.

Indeed and we've even tried using a channel for program and the other for technicians. But I revert back to the issue of Shadows.

[sandall]

But I revert back to the issue of Shadows.

A radiator each side - what shadows?

[sunray]

But I revert back to the issue of Shadows.

A radiator each side - what shadows?

Been there, done it, got the pairs of T-shirts and still shadows cause problems, especially on a flat floor (non raked).We now try to see a user to their seat to make sure it's working for them when sat down, especially little old ladies, and regularly suggest wearing the loop on their head rather than round their neck if it doesn't work.

 

We have quite often used them for walk through presentations (with up to 7 radiators in the same room) carrying different information and as long as the listener is facing the right way there is no problem, so we know shadows do stop the signals.

 

[Stuart91]

Indeed and we've even tried using a channel for program and the other for technicians. But I revert back to the issue of Shadows.

 

That could be quite interesting if the punters can accidentally pick up the technician's channel. Is there some way of locking receivers, or using different ones for the technicians' channel?

 

Although there might be some who would prefer to listen to the show cues.