Induction Loop Systems affecting Guitar Amps?

[pendingrequests]

This is something one of the function band I play in are coming across much more often these days.

Basically, the guitar amps are giving out a serious amount of feedback without being put through the PA. No micing, just plugged into the nearest outlet. If the guitarists, face the front (their back to the amp) we get feedback, yet if they turn around, it stops.

The bass amp is unaffected

We are blaming the hear aid Induction Loop system, which I am still trying to figure out how or why this could be happening or affecting the amps.

Has anyone else heard or this, or happened to them? We are getting quite a lot of bookings form one hotel, where this seems to happen the most oh and the best part: they don't know how to turn it off, or believe it cannot be turned off due to discrimination for the disabled.

Is there anyway around this?

[Longmayyourun]

Yes - this happens to us in one particular local venue. First option is of course to turn off the induction loop, but failing that, try moving the affected amp as it seems the problem is due to some kind of standing wave interference and can be very localised (I'm in way over my head here). Just a couple of feet can make a difference. In our case - lead guitar stage left = howling feedback, rythm guitar stage right (same amp) = no problem at all. I just know it's a royal PITA

[flyfisher]

Are you playing through the venue's sound system? My understanding is that these induction systems connect into PA system, so if you're not using the venue system then its hard to see how it could be active. I also can't see why bass amps should be particularly immune to such interference anymore than guitar amps.

I would definitely be looking to turn the induction system off, if only to test the idea that it is the problem.

I can't see why the system can't be switched off for discrimination reasons though. Firstly because I don't think there's any law that requires such systems to be installed in the first place and secondly if the 'function' is a private affair then surely such systems can't be required.

[Longmayyourun]

A quick ten minutes on google turns up loads of stuff about this, and the majority of thinking seems to be that single coil pickups might be, erm, picking up signal from the induction loop and turning it into a self perpetuating descent into howling uncontrolable feedback, but it is sometimes possible to move out of the critical areas. Having said that - in my band the lead guitar has a problem in this one venue, and is a single coil equipped Strat, but the rythm has no problem and is running humbuckers. As I said before, I'm completely out of my depth here and would love to hear from someone who knows what they're on about regarding this problem. It must have happened to more than two of us??

[flyfisher]

The humbucker thing is fairly easy to explain. Such pickups are wired in such a way as to minimise external interference, usually mains hum. In the case of an induction loop system being connected to the PA then it's quite possible that the system will induce a PA signal into the standard guitar pickup, which is then amplified through the guitar rig, picked up by the PA mics and fed back into the induction loop system. So, a possible howling mechanism is quite likely.

Like any form of feedback, the answer is to break the feedback loop or reduce the gain so that it can't build up into an unconrollable howl.

I really feel the answer is to switch off the induction system. It's actually doing it's job of inducing a signal into anything that can receive it, though that would normally be a suitably equipped hearing aid. Such devices don't, of course, emit high level audio themselves so cannot form part of a feedback loop, whereas an affected guitar and amp clearly could.

The venue staff must surely have someone who understands their in-house PA system and could switch the induction loop transmitter off? If not, the band's sound guy should be able to spot where the device is plugged into the PA. Alternatively, it might be plugged into the venue's intercom system. Wherever it is, it will probably have to be disabled during gigs.

[pete.young]

I've seen both things: problems caused by an unshielded single-coil Strat which disappeared when he plugged in his humbucker-equipped les paul.

We've also had an indiction loop causing problems with both bass and guitar backline which were solved by turning off the loop. If there is a loop, it MUST be turned off because of the potential damage it could inflict on the ears of an unwary passer by with a hearing aid.

[JapanAxe]

This happened to the guitarist in a band I was playing with at the Guildhall in Cheltenham. The system picks up room sound from one or more mics, and feeds it o an induction loop running around the room. Single-coil pickups then pick this up, it comes out of the amp, is picked up by the mics - bingo, feedback. My HB-equipped bass was unaffected. The racket stopped when the induction loop was switched off. Hearing aids have a setting marked 'T' that picks up the induction loop. It would be polite to enquire whether there are people in the venue relying on the system, and who might want it on (at least between sets!)

[Mr. Foxen]

I think the induction loop works at a pretty specific frequency, so should be possible to notch that very specific frequency with eq, and have enough left either side to not notice it being missing.

[pendingrequests]

[quote name='flyfisher' timestamp='1350822139' post='1843794']
Are you playing through the venue's sound system?
[/quote]

Thanks for all the replies guys.

Firstly, no we aren't using the in-house PA. We use our own.

We were actually at the same hotel on Sunday for a wedding fair and once again the feedback was happening.

We are back this Saturday to play a wedding, so we will look into getting in turned off, but from our last time there, getting it turned off seemed to be a problem for the staff. Either no one knew how to turn it off, it couldn't be turned off, or they didn't want us to. Very frustrating, but will try again.

Plugs are few and far between where the stage is, but looking at your results that may not be an issue?


Our Lead guitarist (Stage Right) switches between a Gibson Les Paul, to a Fender Strat after the first 4 songs. Going through a Fender Bassman.
Rhythm (Centre) uses a Telecaster through a Vox. Solid State.

We are having more problems with the Bassman. So we may experiment, with placement if we can't get it turned off.

Keep the solutions and questions coming guys, very much appreciated

[Owen]

Pickups. End of. I have had expensive basses squeal. I have had cheap basses squeal. I have had SC basses TOTALLY shielded. Still squeal. I have had HB basses squeal. We have one in church so I get to experiment with this every week

[Mottlefeeder]

I ran a church PA system with a loop for several years, and some of the comments here are not quite right.

An induction loop is like a loudspeaker coil, and carries audio frequencies - it is not a spot frequency transmitter like a radio, so it is unlikely that you can notch it out.

An induction loop is designed to carry a specific signal level, and the amp has built-in limiters so that it will not cause problems by overloading any hearing aid transducer within range.

An induction loop is often run under the floor, a few feet in from the wall. This gives better coverage, but also gives a dead spot directly over the cable. You may find a location where you do not have a problem..

Passive instruments can pick up even with their volume turned down, because of the way they are wired. Active instruments will not pick up when their volume is at minimum (not much use when you are playing, but might be of use when you stop) Jazz basses have a hum-bucking facility built in to them because the pick-ups have opposite polarity, so they cancel pick-up when when you set the pick-up volumes to be equal - the slightly nasal sound you are left with is the difference in string resonance at the pick-up positions.

The induction loop has to be getting a signal from the band in order to feed it back to them, so if you are using your own PA, look for a live microphone on their system - if you are using their PA, turn down the auxilliary sends.

Hope this helps

David

Edited October 22, 2012 by Mottlefeeder

[pendingrequests]

[quote name='Mottlefeeder' timestamp='1350946409' post='1845561']

Hope this helps

David
[/quote]

Thank you very much David. Great explanation as to why my Jazz bass doesn't get affected as I do in fact keep the pickups at the same level

[pendingrequests]

Just an update guys,

So we were back at the Hotel with the horrendous induction loop system. I asked a member of staff can we turn it off, I got a straight 'No'.

Looking bemused I asked him why not and apparently when they build the Hotel, they build the power amp for the induction loop system [b]within the wall [/b]
allowing no access to it. A well deserved hand clap for the designers.


So we did the gig and yes feedback from both guitarists was happening at the end of every song. Horrid on stage and I am sure out front, but the couple were very happy, so I guess that's all that matters

[flyfisher]

[quote name='pendingrequests' timestamp='1351685017' post='1854097']
Just an update guys,

So we were back at the Hotel with the horrendous induction loop system. I asked a member of staff can we turn it off, I got a straight 'No'.

Looking bemused I asked him why not and apparently when they build the Hotel, they build the power amp for the induction loop system [b]within the wall [/b]
allowing no access to it. A well deserved hand clap for the designers.
[/quote]

I find that hard to believe. I can believe that the induction loop cabling is buried within the wall but what idiot would bury an active power amp? What happens when it fails?

[subrob]

As above. Most loop amps - which are a fairly simple take on any other power amp - won't last more than 5 years, possibly up to 10. The point stands that such devices do yield to the ravages of time, same as anything else, so why risk the redecoration? I deal, by proxy, with induction loops on a daily basis and I imagine that either something exceptional has been set up, or somebody's pulling your leg.

Consider this - if any piece of mains-driven equipment physically couldn't be switched off/ isolated in the venue, in case of emergency, would the local council give it a license?

[Jus Lukin]

-

Edited February 16, 2022 by Jus Lukin

[3below]

Same problem in local hall. Guitar player 1, Gibson les paul, peavey classic 20, severe feedback / high pitch whistle, guitar player 2 Fender strat / Fender valve amp, no probs, Singer using Fender Tele, Fender valve amp, no probs, Me using G&L SB1, Peavey Tour 700, no probs. Conclusion... is not a single coil issue. solved by turning induction loop off.

[flyfisher]

The varying behaviour of instrument/amp combinations could simply be down to their general susceptibility to electromagnetic interference. There are EMC standards for such things these days but I'm not sure if music gear would be covered by the class A or class B (more stringent) requirements. Vintage amps, of course, wouldn't have needed to comply at all.

So, all in all, it sounds like one of those hard to characterise issues but with a simple and easy solution - turn the loop amp off! (assuming it hasn't been walled-up of course ).

[pendingrequests]

[quote name='flyfisher' timestamp='1351691569' post='1854232']
I find that hard to believe. I can believe that the induction loop cabling is buried within the wall but what idiot would bury an active power amp? What happens when it fails?
[/quote]

Well the guy I spoke to had been working there since it was installed (almost 10 years ago from what he told me).

Furthermore, I wasn't in the mood to argue with the guy since he had a wedding to cater to and if i tried to speak to someone else they would have probably said the same thing.

[richardhx]

Seen it so many times. worst are where there is a box on the wall or high up, with a mic built in. You check own system several times, but still no idea until you find the Mic and disconnect the power to the unit. Sucks if there is no switch but there should be a fused spur somewhere.. Hard when time is short.
Seen these feedback on bass, guitars the lot. DDA pretty much means these are left on permanently. My own church has this issue and deaf guitarists. Tell them several times and they still bring the single coil ones in.

My guess is the amp in the hotel is in a service cupboard or a ceiling void. In wall would be a v v odd place to install. Behind skirting boards are possible though.
Bored of telling bands that Single coil is a bad idea - have had to move guitarists far from the perimeter on many occasions. High gain effects do not help this either.