Induction Loop Cable

[pstewart]

I have a vague recollection that running the loop at ear height is the worst possible location for it as the signal strength is low / uneven directly within the loop. When properly designed, the ear height of the listener will be accounted for.

 

This is correct - (bodged physics explanation) The magnetic field exists as a series of circles around the loop conductor - Hearing aids are looking for the vertical component of this. With the loop at ear height, then the signal will be strongest, but also the strength will vary more for small changes in height (head movements). With the loop at floor/ceiling level, small changes in head position are then relatively insignificant, and the signal strength doesn't vary anywhere near as much.

 

Do those portable ones I've seen in the bank manager's office offer better privacy? Lower range I guess? How do they work then?

 

They don't work. We tested one against the standard, and it provided the required field strength for all of about 30cm from the unit. I'm forever having to reject them when builders try to propose them.

 

Philip

[Simon Lewis]

The portable loops are often small units that are designed to sit just in front of the listener on a table. Arguably, these units have limited use, as they typically have to be set up, are often not charged or the user doesn't know how they work, or the talker to listener distance is about the same as the talker to loop mic distance. They are workable small loop systems though.

 

 

 

Counter loops can also be problematic... again the user listens outside the loop, but the loop pad has to be fitted under the counter, where the construction / obstructions / metal surfaces etc. may mean significant compromise in placement.

They do often spill, so it can be easy to eavesdrop a the bank or Post Office.

[sleah]

^^^^^^^^^^^^^^^^^^^ That's the ones!

 

I guess despite their limitations, they are the only solution where privacy is the main concern. (If you have to have a loop of sorts that is..)

[Simon Lewis]

They are immensely popular - probably because it's a one item solution - nothing to install, it can live under some counter somewhere and a label saying"we have a loop if you ask for it" stuck on the window.

Whether it is the right solution in any given situation is more open to debate.

[Yorkie]

I'm installing a loop in a church floor. The floor is floorboards overlaid with new ply and there is a joiner lined up to rout a 4mm groove in the top of the ply for the 2.5mm tri-rated cable. Just seeking advice on how best to stick the cable into the groove before the carpet is installed. PVA? Epoxy? Silicon? just gaffer over the top? Fairly thin carpet I expect so something that would lie nice and flat is best I think.

[timsabre]

I'm installing a loop in a church floor. The floor is floorboards overlaid with new ply and there is a joiner lined up to rout a 4mm groove in the top of the ply for the 2.5mm tri-rated cable. Just seeking advice on how best to stick the cable into the groove before the carpet is installed. PVA? Epoxy? Silicon? just gaffer over the top? Fairly thin carpet I expect so something that would lie nice and flat is best I think.

 

I would just use some sort of tape over the top, probably PVC tape. Gaffa might show through a thin carpet (though so might your groove). You only need to hold it in place till the carpet is fitted.

[Shez]

Any particular reason you're not using tape for the loop rather than cable? Far easier than routing a long groove in the floor!

[Simon Lewis]

Gaffer would do the job. Recessing conduit cable in a groove is probably more robust than copper foil tape but routing out the groove is a pain. Copper tape is much quicker (fit it under gaffer tape) but is more susceptible to the ever present Stanley knives of carpet fitters. Whichever method you use, immediately before the carpet fitter starts, show them the loop cable, show them there is continuity and explain that they will pay to have it made good if they cut through it. Even better, fit a 120dB siren to go off if the loop goes open circuit. That should get their attention just as they slice through! ;-)

[sandall]

Any particular reason you're not using tape for the loop rather than cable?

Expense?

[Stuart91]

If I had the choice, I would definitely go with cable in a groove rather than tape. The cable is more robust in and of itself, and when it's recessed in a groove it'll be much better protected. As Simon points out, carpet fitters are a danger, but tape can gradually deteriorate if there's excessive foot traffic or things like chair legs stabbing at it. Ampetronic sell a plastic extrusion that can be laid over the tape to protect it, but that's more expense and it also leaves a noticeable bump.

[Yorkie]

Having had a look at tape I can see it's cost effective. Something like £50 for 50m of 1.8mm^2 tape vs £25 for 100m of 2.5mm^2 cable - clearly the routing costs though

[Stuart91]

Routing is probably cost effective if you have a joiner on site doing other work, but not if you were getting someone out especially.

[Seano]

Routing is probably cost effective if you have a joiner on site doing other work, but not if you were getting someone out especially.

 

Or have access to a router or laminate trimmer, a reasonable aptitude for that kind of thing and possibly a bit of scrap ply to have a little practice on first.

It's really not at all difficult. If you found it hard to rout a reasonably straight line freehand, it'd be easy enough to tack a bit of batten down to use as a fence (on the left-hand side, as that's the way the router 'pulls' whilst moving forward).

 

I'm installing a loop in a church floor. The floor is floorboards overlaid with new ply and there is a joiner lined up to rout a 4mm groove in the top of the ply for the 2.5mm tri-rated cable. Just seeking advice on how best to stick the cable into the groove before the carpet is installed. PVA? Epoxy? Silicon? just gaffer over the top? Fairly thin carpet I expect so something that would lie nice and flat is best I think.

 

I'd be inclined to work with the joiner as the ply goes down. Rout a slightly bigger groove in the underside of each sheet of ply, or possibly a rebate at the edge of a pair of adjacent sheets (much easier to turn corners that way), and run the cable underneath as the ply goes down. It'd be daft not to mark it's position in sharpie as you go.

 

You'd need a reasonably patient and cooperative joiner as it's a wee bit more faff than just boshing a groove into the top of the ply after it's down, but you won't get better "nice and flat"ness nor more immunity to the carpet fitters' Stanley knives.

 

Edit to add: this is assuming that routing a groove into the original wooden floor underneath the ply is not an option? Or even just sticking flat tape to it.

[adam2]

Did you know that by attaching a high power variable frequency mains voltage motor drive to an induction loop you can actually make all the hearing aids levitate and cause spontaneous combustion of the carpet?

 

I disagree, combustion of the carpet is certainly possible, but surely this combustion is a direct result of the energy input to the loop from the variable frequency drive, it is no more "spontaneous" than the combustion of a tea towel placed on an electric hotplate.

 

Don't feel able to comment on the levitating effect on the hearing aids