Battery-powered induction loops - what is it?

[cinetj]

Hello everyone,

 

I apologize for my ignorance but I've just read this great article at audiomedia.com about the production sound for Les Miserables. At the end of the article, production sound mixer Simon Hayes says and I quote:

 

“It was vital to have the live accompaniment  from the music department but with the amount of 

 

radio frequencies already deployed on the set, I knew I wouldn’t be able to use radio systems for the actor’s earpieces, that just wasn’t going to be possible.

 

“However I had used battery-powered induction loops in Greece for Mamma Mia so myself and my 

crew have extensive experience in the ‘black art’ of induction! We sourced the highest quality loop 

amps we could, and with a suitable range of power outputs to cover the set sizes we tried to deliver the best audio quality possible across a whole range of set ups and stages.We used up to 75 hidden earpieces at once on the big chorus numbers. This is in addition to a wireless feed of the mixed piano and vocals, a clean piano feed, and the usual camera feeds and boom talkback feeds. All this resulted in a significant amount of induction and wireless infrastructure that 

had to be rigged and ready to go at each location."

 

Does anyone here know how this black art is made? I've never heard of it and couldn't understand much of the above.

[john Quinn]

How do induction loops work?

An induction loop system transmits an audio signal directly into a hearing aid via a magnetic field, greatly reducing background noise, competing sounds, reverberation and other acoustic distortions that reduce clarity of sound.

This diagram illustrates how they work.

Audio Inputs 1, either from an existing audio source such as a P.A. system or from dedicated microphone inputs feed an audio signal into an Induction Loop Amplifier 2. The amplifier drives a current into a Loop 3 or series of loops. As the current flows through the cable it creates a Magnetic Field 4 in the required area – careful loop and amplifier design ensures that the vertical component of the field is even and free of dropouts and dead zones wherever the user might be. Inside most Hearing Aids 5, a small coil known as a Telecoil 6 picks up the magnetic field signal, which is amplified into a high quality audio signal delivered directly to the ear of the hearing aid user.

 

 

It is really very simple the hardest part on set is wrangling the cable and keeping the earpieces turned up.

 

Best John

[John Blankenship]

http://www.professionalsound.com/specs/inductive.htm

Commonly referred to as an "earwig," these can pick up a signal either from an induction loop worn around the neck,

http://www.comtek.com/rc216.html

or from a large induction loop surrounding the stage.

(The writeup at the first link explains it pretty well.)

[Solid Goldberger]

Just curious why "traditional" wireless Phonak earwigs would not be possible? It would seem like they'd just need one additional frequency, which I'm sure could be squeezed in.

 

Is there some other advantage to an induction setup that i'm not aware of?

 

e.

[Jeff Wexler]

The biggest advantage (and this applies to Simon's use of induction earpieces) is that it does not rely on wireless frequencies. On Les Mis they had a huge amount of wireless gear working and the earpieces would have added just one more layer of complexity. Sure, they probably could have found an open frequency but I'm sure they determined that using induction earpieces was a better and more efficient way to go.

[johnpaul215]

It is interesting. If they we using induction loops, then everyone is getting the same feed. If they were using an RF based monitor, it would be only one signal that everyone was tuned to. I've never used induction setups. How does the sound quality compare to other options? This is to sing along to, not for a scripty or note taker, so I would thing they would want something a bit better than Comteks.

[john Quinn]

The sound quality is rubbish but that does not matter as it is only being used to keep everyone in sync, but it is most likely as good as any other mini earpiece based system

Best John

 

 

  PS         I have used induction loops many times over here in the UK they seem to be the traditional thing to use when dealing with music playback where you also want to record live vocals, they are also perfect for night club scenes when you need extras to dance in the back ground while recording dialog  .I have also used Wisycoms in ear transmitted monitoring systems but that was generally when feeding talkback to a presenters.

[cinetj]

Thank you for both of your answers, John Quinn and Blankenship. Now, I'm able to understand the process a little better. Regarding the neck loops, does anyone have any picture of those used by an actual actor or performer. Just thinking that It would be nice to strangle an actor once in a while.

 

 

http://www.professionalsound.com/specs/inductive.htm

Commonly referred to as an "earwig," these can pick up a signal either from an induction loop worn around the neck,

http://www.comtek.com/rc216.html

or from a large induction loop surrounding the stage.

(The writeup at the first link explains it pretty well.)

[John Blankenship]

The loop is shown on the Comtek page I referenced and is worn hidden under their clothing.

A Kevlar-reinforced lav cable might work better for strangling talent. I prefer to hint at the menace of a vampire clip on their chest to keep them in line -- thus preventing the need for strangulation. I find that strangulation tends to slow down production as there is a great deal of paperwork involved after the fact.

[cinetj]

The loop is shown on the Comtek page I referenced and is worn hidden under their clothing.

A Kevlar-reinforced lav cable might work better for strangling talent. I prefer to hint at the menace of a vampire clip on their chest to keep them in line -- thus preventing the need for strangulation. I find that strangulation tends to slow down production as there is a great deal of paperwork involved after the fact.

 

Good point and nice ideas for torturing talent as yours are always welcome.

 

Looking at the picture of the comtek unit, the neck loop seems actually pretty small. Hence my doubt: it can be anywhere on the body of the actor, not necessarily the neck, right?

[John Blankenship]

It's designed to go around the neck as that can easily be out of sight and still close to the receiver in the ear. The receiver would then typically be at belt level (or higher).

[studiomprd]

" why "traditional" wireless Phonak earwigs would not be possible? "

Induction system is traditional,  wireless versions have only recently become practical and popular; the wireless earwigs are noticeably more expensive

BTW, Phonak's main business is top line (premium) hearing aids.

 

Induction loops replace speakers at the output of audio amps; looping a room requires a significant amount of power,  neck worn loops can work with the puny audio power output of a little RX like a Comtek

[Philip Perkins]

The all-in-one "Invisity" type receiver /bugs are about 3 times as expensive as the simple old earwigs, and have to be tuned.  I have had issues with reception with them, even with a strong Comtek TX.  But not having to hide a neck loop AND a Comtek RX is great, as is avoiding the room-loop muck-around....

 

philp

[Peter Mega]

I've been using induction loops and earpieces on alot of shows I've been working on for the past few years.

My current show requires a room loop which I've sourced from

http://www.c-tec.co.uk/products/inductionloops.htm

I'm using the DL50 which is designed for domestic use but fitted our needs and room size. They do a pro range for theaters etc which has huge coverage which was overkill for our show.

I'm using Comtek IR230 earpieces which are a T coil type (telecoil) earpiece.

It all works but is limited to the quality of the loop (any brand) and earpiece which is adequate for our needs. The beauty of having a neck loop and personal receiver like Lectro R1a is the talent has their own volume control which the don't have with the room loop system and it can only be cranked up so much before sounding distorted and bad.

Another show I do, we use my Lectro R1a with neck loop and custom moulded earpieces for the hosts. Works very well and has great Lectro range.

Many ways to skin a cat and generally most work well but each has downfalls.

The room loop has volume issues, but no personal receiver like R1a to hide on talent.

R1a with neck loop has individual volume control but needs hiding on talent which can prove tricky with women in minimal/tight clothing along with a radio mic transmitter to hide.

Lectro ifb tx and rx systems can also be set up as discreet sends for each talent with a PTT mic switching key panel.

YMMV

Cheers

Peter Mega

[john Quinn]

I did a shoot recently where we used neck loops, at one point we were filming under some railway arches .The electricity running through the overhead power cables did cause quiet a hum on the earpieces.A bit annoying for the cast but none of these systems are perfect.

 

Best John

 

http://christmascard2012.crisis.org.uk/d88c8450/

[Aron Siegel]

how would you make your own induction loop using an amplifier and what kind of cable would you use with it?

 

Also, I have about 5 of the phonak ear pieces with some older comtek loops.  some of my loops need to be replaced or repaired.

 

from what i'm reading, it seems that regular t-coil hearing aids will work with both of these induction loops as well?

[studiomprd]

" how would you make your own induction loop using an amplifier and what kind of cable would you use with it? "

I have made several, and use multi-conductor cables --now a days, cat 5 will provide 8 loops!

wire the loop with a junction box of some sort, so that the signal goes round and round, (oh-ohhh oh) and comes out after making as many trips around the loop as the conductors permit. (the idea is that it is a big induction coil!

another reason for the multiple loops around for the audio is that the coil (loop) must present a reasonable impedance match (usually at least 4 ohms) for the audio power amp...

Edited February 9, 2013 by studiomprd

[Mirror]

I did a huge musical show in the '80's that required the frequent use of earwig payback via induction loop cable and amp.  The induction cable was long, I want to guess 25 years later it was 300' long. On one set we were pre-rigging, the cable had to be under a small raised platform.  As we were crawling through the 2 foot risers of this platform we came up with a brilliant thought, "If once around is good, three times around will be better!"  We finished just in time for Etta James to hit the stage.  Fail.  The triple wrap caused a huge amount of cancellation zones on the stage.  We ended up abandoning that loop and ran a single loop around the perimeter of the set.  Lesson learned. 

[Philip Perkins]

I did a huge musical show in the '80's that required the frequent use of earwig payback via induction loop cable and amp.  The induction cable was long, I want to guess 25 years later it was 300' long. On one set we were pre-rigging, the cable had to be under a small raised platform.  As we were crawling through the 2 foot risers of this platform we came up with a brilliant thought, "If once around is good, three times around will be better!"  We finished just in time for Etta James to hit the stage.  Fail.  The triple wrap caused a huge amount of cancellation zones on the stage.  We ended up abandoning that loop and ran a single loop around the perimeter of the set.  Lesson learned. 

Had same experience.  In my case the stage had a metal covering, to boot.  But one loop of relatively light wire around the stage driven by a 100w amp did the trick.   Little kids, so after I got the wardrobe people talked down about the mic TX there was no way I was going to get buy in for adding a Comtek RX to their outfits.

 

philp