Magnetic screening of the pit

[boswell]

I know nothing about electric Guitars, but we have a problem with the electric bass guitar in the pit picking up the magnetic deaf aid loop and then going into feedback.

Can electric bass guitars use any other type of pickup that is not sensitive to magnetic loops? if so which? :unsure:

[paulears]

Well - like any electric, they could use double coil pickups (hum-buckers) or the guitar could be fitted with individual string synthesis/sampling systems like the variax ones, or even midi pickups - but the majority of instruments have pickups for a particular sound. If the audio loop has been poorly installed, then the problem is often impossible to solve without changing instruments - and, as the player will tell you, there is nothing wrong with his guitar, it just can't tell the difference between string and loop! Many loops are run around the perimeter when they could have been profiled to avoid the pit and stage area.

 

I assume you have experimented with different positions in the pit?

[boatman]

A delay in the feed to the induction loop amplifier might fix it, but will probably upset the audience members who, like me, have only one hearing aid.

[weatherhead]

Your bassist is likely to be very reesistant to changing his pickups for this reason, especially if it's going to be at his cost!

[Solstace]

...especially if it's going to be at his cost!

 

Seconded!

 

On a more constructive note - from the OP's notes it sounds like the bass is being mixed into the signal sent to the loop amp. Assuming the pickups can't/won't be changed - could the sound operator remove the bass from that mix? For all affected instruments, I find that doing this AS WELL AS ensuring the musicians turn their amps off during "talk" sections is usually as failproof as any human.

[boswell]

Bit more info, the Bass is not fed directly into the Loop. The Loop amp has a mic hanging over the stage as its only input, if we turn the gain down on the loop amp then speech is not loud enough over the loop. The loop is a seperate system not directly connected to the sound system.

The pit were complaning that the bass was too loud in the pit (Local amp) and wanted the bass fed into the stage foldback monitors so they could turn their amp down in the pit. Reasonable request, espescially with the new sound regs!!

So the bass (along with keyboard) is being fed into the foldback monitors via the desk, being picked up by the loop mic, sent out over the loop and being picked up by the bass pickup so completing the chain and feedback.

Have tried using EQ on the bass channel on the desk but the MD & Guitar player complained that the 'sound' of the bass guitar was lost.

I don't think its the bass notes causing the trouble, as it can go into feedback without playing a note, it's more that the bass pickup is responding to the loop signal and then we are feeding it back into the loop mic input via the Foldback monitors

 

I think I'll tell the bass player that if he wants to feed his bass into the system then he will have to find a pickup that is not affected by the loop or put up with a high level in the pit!! :)

 

The loop layout is optimised for the the best audience coverage. If we move the loop cable away from the pit towards the audience then the first few rows will have reduced signal levels and be more sensitive to orientation of the deafaid(We tried this during the install of the loop)

 

Our audience average age is 60+ with quite a few 90+ so turning off the loop is not an option!.

You want to see 80 year old ladies screaming at 'The Full Monty' :unsure:

[paulears]

If I was the bass player - I'd be tempted to tell you where to go (from his perspective). There are only two workable alternatives - borrow a different guitar that may be less problematic, or get him to play through his amp at a lower volume than he wants. He's already annoyed having his control being removed from him and passed to the sound dept. I hate this, and find it very difficult to play. The simplest possible solution is to try and get a guitar swap, but putting everything through one monitor mix would be totally and utterly unacceptable to most musicians - they need to hear themselves. If you have your instrument through one speaker, and the band in another, you can mentally separate them, but having them all through one speaker is a real messy problem.

 

Sound level is likely to be worse - as all these sources will need to be potent, and sitting next to a bass amp at X volume is less trouble than a mix at the same level.

 

Why is it that the musicians needs are rarely taken into account? Get a painter in to paint a portrait and say "I'd like a realistic painting please, but I don't want you to use both eyes, and can you not use Blue????"

 

If you are doing the Full Monty, the band have some LOUD songs to play - have you tried screening? I've not tried it, but how about a foil or mesh grounded panel between the guitar and the audience?

[pattonaudio]

So the bass (along with keyboard) is being fed into the foldback monitors via the desk, being picked up by the loop mic, sent out over the loop and being picked up by the bass pickup so completing the chain and feedback.

I don't think its the bass notes causing the trouble, as it can go into feedback without playing a note, it's more that the bass pickup is responding to the loop signal and then we are feeding it back into the loop mic input via the Foldback monitors

 

 

I have come across a smilar problem to this in the past, it turned out the solution was simple, we just moved the FOH & Monitor amps as far way from the Induction Loop Amp as possible.

 

So my suggestion although it may seem to be the bass pickup, is to experiment with the position of the bass players guitar and amp and also don't rule out the monitor amps.

[boswell]

The monitor & FOH amps are 17mtr away from the outside of the loop and don't pick up anything any other time. Good point about the guitar amp tho' I'll try to get it moved in the pit.

[Doug Siddons]

Just a quick tuppence on this one, I would check the bass players lead and make sure its properly shielded and of high quality, also check the shielding and earthing in the bass as this is usually the quickest way to make a bass microphonic, would be interested to know if the problem reduces if the player backs the bass guitars volume control back a little bit as it could be a problem with his volume control on the way out or just being a cheap component

[Simon Lewis]

...I would check the bass players lead and make sure its properly shielded and of high quality, also check the shielding and earthing in the bass ...

 

Although the loop could be picked up by these devices, it's more likely to be picked up by a coil of wire - which is why the instrument's pickups are supect. Orientation can make a big difference, so getting him to turn 90 degrees can sometimes solve the issue. Magnetic shielding is rarely achieved using screening - you need to use something like mumetal.

 

Is it possible to feed the loop from the desk, instead of using an overhead mic? The mic approach rarely delivers the best intelligibility anyway ;-)

 

Simon

[david.elsbury]

Can you DI the bass and give the player headphones, possibly with a local mic mixed into his cans for ambience?

[paulears]

The bass would still be coloured by the loop though, so would no doubt sound odd, but if you fed this through the pa, and into the loop it feedback again?

[Lufty]

try reversing the loop connections , this can sometimes have a significant effect , In one of the local churches I have a changover switch fitted ready for any such problems

[themadhippy]

One other thing worth checking though not so common on bass amps is the old spring line reverb units.