Induction Loop coming through Speaker

[Jwaugh]

HI

 

In my Church we have a set of EON15 G2 Powered Speakers, which are behind the pulpit, connected to our Electronic Organ.

 

Last week I discovered that the Speakers are picking up what is being sent through the induction loop.

 

Anyone know how this is happening and how to stop it.

 

 

John

[adamharman]

The loop puts out a signal at audio frequency, any loop of wire will pick it up to some extent. My guess is that you've got a loop consisting of the screening on the leads from the organ to the speakers, and the earths in the mains leads. Isolating transformers (ground loop isolators) in the signal leads should solve it. A lot of smaller keyboards aren't connected to mains earth, so could just be a loop through the signal leads and the speaker earths. Does it still do it if you unplug one speaker?

[Jwaugh]

Does it still do it if you unplug one speaker?

 

 

HI Thanks for the reply. I will go up some night this week and check. Will also look at the leads and see how they are wired.

 

John

[timsabre]

Any unbalanced audio cabling will pick up the loop. You don't say how the organ is connected to the speakers, but if it's jack cables, they will do it. Sometimes the instrument itself can pick it up.

Adam's earth loop suggestion is good too.

Induction loops can be a bit of a nightmare, in our church we have to use transformer DI boxes for all instruments with the earth lift switch set to "lift" otherwise we get the induction loop signal in everything. Also we moved the loop cable so that all instruments are well outside the loop.

[Simon Lewis]

Loops are good - so don't be tempted to just turn it off ;-)

 

However, the signal can get in several ways. As mentioned above, unbalanced cables be susceptable, as can guitar pickups and even dynamic mics.

Moving the item outside the loop will reduce the signal magnitude but not stop it, as the field radiates up to 4 loop diameters away.

It is possible for loop signal to be picked up if the loop amp and audio amp are separated by some distance (i.e. at different points on the ring main etc.). Try running an extension lead from where the loop amp is plugged in to one of the Eons and see if the signal is still heard through it. Check that you do not have audio signal cable running alongside the loop for any distance, and try orientating leads at 90 degrees to the loop cable.

 

Make sure that where the ends of the loop cable meet and go to the loop amplifier, that they are twisted together all the way to the amp terminals. This reduces radiated signal next to the amp.

 

Try disconnecting all stage inputs and desk outputs, connect up the loop I/p & o/p and try the Eon to see if you get loop pickup. If you do, check teh mains and signal wiring as above, or try the Eon at FOH to see where the fault lies, If it's clean, try adding in the rest of the inputs one at a time.

 

Lastly, what are you feeding into the loop? If it's the whole mix, might I suggest (if possible) you feed only the sources that are really needed? I woudl include only vocal mics, a lead instrument and all the radio / pulpit mics etc. There is usually enough bleed to not need an ambience mic, and often the inclusion of such a mic actually degrades intelligibility.

 

If you want some more tips, the go to the Ampetronic website and request their loop installation / design handbook.

 

Let us know how you get on!

 

Simon