Induction loop questions

[henny]

hi all

 

I have a few questions regarding induction loop installs.

 

1) how well do loops behave in suspended celings? eg running the loop overhead in the celing?

 

2) I have one room that splits in to 2 , so will need 2 systems is there any way to prevent cross talk? or do I just talk the client in to using an ir system for all the 6 rooms im doing?

 

thanks

 

ian

[paulears]

ceiling loops are quite unpredictable. Ampetronic have a decent amount of data on their website, but in my usual way I ignored their advice about (one) not having loops above, and (two) keeping them away from metal (as in the ceiling tile suspensions).

 

The ceiling route was by far the easiest to install, so a test was in order. The loop circumference was 95m, 1.5mm cable was within spec so I laid it carefully around the auditorium roof. In this theatre it is reasonably easy to get to with timber walkways just where they are needed. The aluminium supports were themselves supported at approx 7.5m centres by rsj's. Wandering around the auditorium produced very variable results - levels went up and down, and there were fairly severe tonal changes. I have no way of actually quantifying the radiation pattern, but it was pretty poor.

 

The floor was timber, with a mahogony top surface (I presume this was before the days of ply), covered with a lino like top surface. I laid the same cable on the floor, directly under where it had been in the first test. The ceiling is not that high, around 10m at the stage, reducing to 4 at the rear.

 

The floor cable was very different. Tonaly, much better and hardly any variation as I walked around - volume was also much more consistent.

 

Result was 3 days cutting a grove in the floor and filling it in. Don't get me on B&Q colour matching - "don't worry, the colour darkens as it dries........" Oh no it didn't!

 

The loop output drops off quite quickly as you move out of it, the trick is making sure the loop doesn't extend to much towards the other one - so if the gap is big enough you do get workable separation. Ampetronic are great for giving advice - let them have the spaces and they'll work out if what you plan will work in practice.

 

Hope this helps. I've installed loads of loop systems in the past few months (3 more to do tomorrow, hopefully simple installs)

paul

[Solstace]

I'd suggest IR is the way to go - my church made the transition recently and it's saved a lot of headaches. Means we can use the crypt PA without getting inducted crosstalk coming through!!

[Chris_R]

Id echo the infrared recommendation. Although I've never directly used an IR hearing aid loop our non-IR loop at church causes crosstalk, especially in the monitors (which is a bit of a pain!) and can cause feedback in some cases.

Hope this helps!

[Simon Lewis]

hi all

 

I have a few questions  regarding  induction loop installs.

 

1) how well do loops behave in suspended celings? eg running the loop overhead in the celing?

 

The aluminium can cause eddy currents, so it's best to trial the loop first and then check for field strength and frequency response. You'll need a field strength meter and a calibrated receivedrhooked up to a decent meter (I use Smaart).

 

Depending on how high the ceiling is, and how much metal there is in the building, the results can vary from reasonably acceptable to unusable.

Remember too that the different manufacturer's amps actualy sound quite different as well.... ;-)

 

2) I have one room that splits in to 2 , so will need 2 systems  is there any way to prevent cross talk? or do I just talk the client in to using an ir system  for all the 6 rooms im doing?

The only way around this is to go for a low spill design. Contact Ameptronic, and they will design one for you - probably cost around £100 or more for the design, and you will need multiple loop amps to run in phase quadrature, and have access to the floor / ceiling to run the loop pattern (i.e. it won't be a perimeter loop).

 

Infra red does solve the problem of cross room interference, but can itself be affected by sunlight in older systems and by fluorescent tubes. Check the modulation frequency, and how many channels there are available (you'll want to be able to use the same receivers in either room, so two makes sense).

 

Those with hearing loss often dislike IR receivers as they reveal that they are "different". Cinemas aren't as problematic (you sit in the dark) but other public spaces tend to keep the lights on....

 

Lastly, whichever system you go for, do a background EM noise survey first. Recent studies we've carried out show that the majority of counter loops fitted in public spaces in Derby either don't work, or have an unacceptable signal to noise ratio. Some of the church installs I carry out have split neutrals on the lighting system which generates high levels of 50Hz and its harmonics - again making a loop completely unusable.

 

[rant] I've installed loops for over 20 years now, but I'm exasperated by some of the recent installers (Paul - I'm sure you do it correctly!). Several in the area profess expertise, but the finished system is often poor or simply doesn't work. DDA is being paid lip service to, and the real needs of those with hearing loss is being missed! [/rant]

 

Simon

[J Pearce]

Our church system runs in the floor, but you may find you will get feedback/crosstalk from guitars.

 

Our solution is to run the loop off of a post fader aux send and cut all guitars from the loop. Then silence guitar amps when not being used.

Its not particularly elegant but it works

[Bryson]

I used to favour IR, but having run a fair few IR systems for a while, I'm not so sure anymore. The problem is not in the technicalities of the system, but the practicalities. With a loop, the receiving equipment belongs to the user - so everyone that needs to use the system has a personal set that they ensure works.

 

With IR, you end up with all the headaches of handing out headsets, making sure your FOH staff (who may be casual or transitory) understand what it is, and are able to explain why that person's hearing aid wont work, plus having to clean the headsets, make sure they're charged, make sure they work, make sure you have enough, make sure the forgetful old ladies don't wander off with them etc etc etc.

 

I think the practical superiority of a loop system outweighs the technical superiority of the IR systems, for any public entertainment application.

[paulears]

I agree with Bryson - the practicalities of looking after IR are too great for us to even consider, and I'd be worried about people zipping out the fire exits and forgeting to hand them back - IR may be sonically better and perhaps more manageable, but the venue need to look after the tx and rx end - with loop, the rx is the wearers responsibility which suits me better.