Induction Loop Cable

[Bazz339]

As per title .

What type of induction loop cable do people use, specifically for surface mounting in churches.

 

I tend to use single core tri rated largely because of the CSA and colours available.

 

Anyone use twin core flex or other?

[dmxlights]

You cannot use twin core flex unless you wire the cores as one and do the full loop of the room and back to the induction loop unit. what I use manly is single core 1mmsq cable used for lighting and never had any problems with it.

 

The other thing with induction loops the cable has to be run at floor level all around the room. You can go up over the doors and come back down the other side. I know this as I have installed a few and I am also partially deaf myself which come in very handy for testing loop systems after in its installed.

[alistermorton]

I've seen a design for a portable induction loop that used ordinary 1.5 mm 3 core mains flex. The cable (a 50 m reel I think) was "terminated" in a cable drum at one end, and a 3 pin XLR at the other. On the drum was a matching XLR and a jack socket, the idea being that the cable was unwound around the room and then plugged back into the reel. This connected the cores together to form a three turn coil, the ends of which were connected to the jack, which went to the amp.

[bruce]

The other thing with induction loops the cable has to be run at floor level all around the room. You can go up over the doors and come back down the other side.

 

That's a slight oversimplification - the critical point is that the loop should NOT be at listener level!

 

Generally, you'd assume for a seated listener that the "lister level" is about 4 foot off the ground. A simple loop needs to be either above or below that level, by roughly a sixth of the loop width.

 

So floor level is fine for a room of 8m width. But ceiling level is often equally good.

[themadhippy]

ive use flat sticky backed plastic copper tape in the past,no lumps,even under the thinest carpet,sticks directly to the wall and soon disapears with a coat or 2 of paint

[Simon Lewis]

Tri-rated is fine and is widely available in different csa and colours.

 

The cross sectional area should be chosen by referring to the manufacturer's information for loop aspect ratio and loop length. One size does not fit all installations.

Single turn loops fed from constant current amplifiers are the most common large area loop systems. It is possible to do mutliturn loops (with voltage source amp), but also quite possible to do them badly, so the single turn loop is usually preferable.

 

Therefore, I would not use twin flex or any other cable, unless it was twisted feeder cable from the amp to the start of the loop.

 

Bruce helpfully points out that loop height / displacement from the listening plane is a function of room size / layout. There are occasions when mounting about 1.2m above listener ear height is better than at floor level.

 

I get to test a large number of loop installations.... unfortunately, many range from poor to utter tripe....

[bruce]

The under-carpet copper tape is great, especially if you are designing a low-spill system.

 

But, even if you install protection, beware of carpet fitters and stanley knives.

 

 

Ampetronics offer a very good, and usually free, design and verification service.

[timsabre]

ive use flat sticky backed plastic copper tape in the past,no lumps,even under the thinest carpet,sticks directly to the wall and soon disapears with a coat or 2 of paint

 

It's a lot more expensive than normal wire though.

And don't let carpet fitters anywhere near it. We used some in our recent church refurb. We showed it to the carpet fitters. We covered it in warning tape. They still cut it in 6 or 7 places.

 

Multi-turn loops are not recommended because the inductiveness of the loop starts to cause problems - or at least that's what Ampetronic say.

[Simon Lewis]

ive use flat sticky backed plastic copper tape in the past,no lumps,even under the thinest carpet,sticks directly to the wall and soon disapears with a coat or 2 of paint

 

Copper tape can be extremely useful, especially if creating cancellation based loops or phased arrays. It does have some caveats though. Care needs to be taken if used direct on concrete floors (especially new ones) and carpet fitters have a genetic disposition to cut through copper tape hundreds of times. Colleagues at Ampetronic have been known to leave a small but loud alarm connected to the newly installed loop cable so that if it goes open circuit, the carpet fitter can be blamed straight away!

 

Edit... beaten to it!

However, I second the comment regarding Ampetronic - they know their stuff and are extremely helpful!

[Bazz339]

You cannot use twin core flex unless you wire the cores as one and do the full loop of the room and back to the induction loop unit. what I use manly is single core 1mmsq cable used for lighting and never had any problems with it.

 

 

You can wire the cores in series resulting in a stronger magnetic field providing the impedance is within the range for the amplifier. The down side is that there may be a loss of HF

[Simon Lewis]

You can wire the cores in series resulting in a stronger magnetic field providing the impedance is within the range for the amplifier. The down side is that there may be a loss of HF

 

The upper frequency response (already deliberately truncated) would suffer. If building steel is present, the potential resultant metal loss will see signal loss, especially at high frequencies. Increasing the inductance of the loop is therefore not usually a good idea.

There's also the possibility of providing too strong a magnetic field. Given that we need to achieve 100mA/m(with peaks of 400mA/m) 100Hz-5kHz, it is best to stick to the loop layout that the amplifier is designed for.

[paulears]

Ten minutes on the phone to Ampetronics showed me that my knowledge of loop systems was embryonic to the extreme. Some research brought up factors like Simon mentions, and I still don't really understand much apart from the basics. My few installs, looking back, were probably flukes!

[bigclive]

Oh yes. Copper tape and carpet fitters.

 

I've spent many a lovely afternoon crawling about on new carpet with a signal tracer, stanley knife, soldering iron and glue to stick the slit in the carpet back down.

 

And if anyone tells you that you can fix a break in the tape by sticking another bit over the top and stabbing it with a sharp point a few times, just ignore them. The correct fix is a bit of bridging tape or wire soldered across the cut.

[dbuckley]

I read this topic with trepidation, as on more than one occasion Mr Lewis has caused my keyboard to be covered in beverage...

[bigclive]

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?