Tech: PA goes berserk

Subject: Tech: PA goes berserk
From: leeneia
Date: 07 Dec 19 - 11:55 PM

Two hours ago we were having English country dance at a local church. The callers use microphones attached to a PA system tucked in a closet, but nobody had a mic on when it happened. The mics were lying on a table about 40 feet away from the PA, with all its dials.

What happened was a loud, raucous, scratchy blast of sound which had people all over the room throwing their hands over their ears. Our guitarist screamed from the pain of it, while I scanned the ceiling, looking for the roof to come down.

The system had operated fine before that: from 6 pm to 9:30.

Any idea why something like that would happen?

Our leader raced to the closet and shut off the power.

Subject: RE: Tech: PA goes berserk
From: BobL
Date: 08 Dec 19 - 07:53 AM

"Tucked in a closet" - so presumably it was the house PA system?
"Loud, raucous, scratchy blast of sound" - but you're not a heavy metal band...

If the problem suddenly cropped up without anyone touching anything, then it could indeed be a fault somewhere - anywhere - in the PA system. Main amp, one of the channels, something plugged into it. You don't say if the mics were wired or wireless: wireless mics can pick up interference. Did anyone try to track down the problem afterwards? Like by disconnecting everything and turning all volume controls to zero before powering up the system again? That's how I'd have started looking into it.

Subject: RE: Tech: PA goes berserk
From: GUEST
Date: 08 Dec 19 - 03:33 PM

If wireless mica then I think depleted batteries in transmitter is a good candidate for such as you describe.

Subject: RE: Tech: PA goes berserk
From: GUEST,Mind the Mess
Date: 08 Dec 19 - 07:39 PM

Maybe the PA suddenly got the punchline to a joke it heard last week, and couldn't help but do the electronic equivalent of slapping one's forehead.

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 08 Dec 19 - 10:33 PM

Thanks, Bob L and Guest. They were indeed wireless mics. What do you mean by 'pick up interference'? This is a big city, so there are trucks, trains, planes and helicopters around. But why would a radio produce uninterrupted static for a long time?

I remember when a PA system would occasionally pick up words from the CB's of passing truckers, usually IIRC, with a blast of static. But I haven't heard that in a long time. The noise that we heard Saturday night seemed to last a long time - long enough for everybody to freeze, and look around in confusion, and for our leader to run across a sizable public room, open the door and turn off the PA. Who knows how long it would have gone on if left alone?

At any rate, it wasn't the usual 2-second blast of static. I'm sure there were a lot of thudding hearts in the room for a while.

The church, of course, will deal with it, not us. Nonetheless, it's good to know there are logical explanations - dying batteries, interference, or a fault in the system. But it's funny that the thing worked perfectly for three hours prior.

The noise stopped, and after a few seconds we resumed the playing of the final couples' waltz. The sweet music seemed to soothe everyone's battered system.

Subject: RE: Tech: PA goes berserk
From: GUEST,Lou sound guy
Date: 09 Dec 19 - 10:03 AM

!. a sound system needs a skilled operator. You wouldn't put a fiddle on stage without a qualified player would you? Having a sound system unattended by a competent professional is asking for embarrassment and hearing damage. (same as a fiddle!)

2. Wirelss mic receivers wil amplify whatever they receive on their specific radio channel. They have a "squelch" control (usually on the back of the receiver) which will silence the random RF noise that is in the air everywhere. The operator needs to turn the system on, have the mic transmitter OFF and bring up he receiver slowly until the noise is heard, then adust the squelch to quiet the random noise, then turn on the mic trnasmitter to check the sound. Too much squelch with make the mic cut out occasionally, to little will let the noise through if the mic's signal drops, it is turned off, or the battery dies.

See why you need a professional? We are worth twice what anyone is willing to pay!

Subject: RE: Tech: PA goes berserk
From: treewind
Date: 09 Dec 19 - 12:07 PM

Depleted batteries in a properly set up wireless mic simply make it go silent.
If the receiver has a squelch control and it's incorrectly adjusted you'll get a very loud hiss (like escaping steam or you're standing next to a waterfall.)

The mics have been mentioned, but they aren't necessarily to blame. There was a guitarist mentioned, so there were probably some other instruments too. It could have been any amplified instrument, the mixer or the power amp. Electronics, power supplies, loose connections... almost anything.

"it's funny that the thing worked perfectly for three hours prior. "
What's more disconcerting is that it carried on working normally afterwards, so it's going to be hard to find out what the fault was.

The worst interference I remember while playing in a band was in a place in the 1970s that had a "one armed bandit" gambling machine in the bar outside the back of the hall. The clunk-clunk-clunk of a payout was accompanied by a simutaneous series of loud cracks from the speakers of our PA.
Proper balanced mic cables and inputs were rare in those days, and cheap home-made PA systems (like ours) with 1/4 inch jacks were commonplace.

Subject: RE: Tech: PA goes berserk
From: punkfolkrocker
Date: 09 Dec 19 - 12:16 PM

How old is the wiring in the Church,
when was it last tested by a qualified technician...???

Power surges.. spikes...???

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 09 Dec 19 - 12:46 PM

We didn't turn it on again.

We'll let somebody with hearing protection in place be the one to check it out.

Subject: RE: Tech: PA goes berserk
From: Vic Smith
Date: 09 Dec 19 - 12:49 PM

I was calling a dance at the Metropole Hotel in Brighton (yes, that one) and using my radio mic. Suddenly my voice went incredibly loud and we had not touched the PA. However much we turned it down the mic could be heard throughout that floor of the hotel. It took us a while to realise that the loud sound was not coming through our PA but from the disco speakers that were to follow us. Disco had set up his gear and then put in on a timer and his radio mic must have been on the same frequency as mine. We unplugged his gear at the wall and carried on and managed to recover the excellent atmosphere that we had created earlier.
When Mr. Disco returned, he wanted to know angrily who had unplugged it and when we told him it was us and asked why he had put his equipment on a timer - it had nearly ruined our part of the evening, He said that he needed to warm his equipment up. One of the band told him to stop talking bollocks, but he continued to rant at us. It was a posh do with an event organiser and she came up to ask what was going on. She had been there when the huge increase in volume has happened. First she apologised to us than told the disco bloke what she thought of him in no uncertain terms. He stomped out of the room in a huff.
The disco was scheduled to follow our dance smoothly and straight away. By the time we has packed up and were ready to leave, he hadn't returned.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 09 Dec 19 - 01:15 PM

It’s difficult, if not impossible, to diagnose what might have been responsible but my guess would be a piece of old and badly maintained (unstable) equipment.

Whilst we’re on the subject of radio mics, I was once setting up a system for a musical and a roadie was on stage saying “one - two”, “one - two”, “thirty six”, “twenty eight”, “forty five” etc etc when the rear door of the theatre burst open and in came an angry man asking if we were using a radio mic? “Yes” said the roadie, “six of them”. “Well I’m the bingo caller from over the road and it’s breaking through my system” he said. “We’ve got a license for ours” said the roadie “have you?” at which point he retreated never to be seen again!

Subject: RE: Tech: PA goes berserk
From: treewind
Date: 11 Dec 19 - 10:48 AM

"we've got a license for ours. Have you?"
Radio mics are commonly used on frequencies that don't need a license (at least I think they used not to need one) but that's a very good line to try, even if it's just calling their bluff!

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 11 Dec 19 - 11:10 AM

Both he and I knew that but he was guessing the bingo caller didn’t.

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 11 Dec 19 - 12:40 PM

The mystery about the loud blast of sound has two parts.

1. The volume was set to a certain comfortable level. This means that the power which the unit was permitted to use was limited. How did the blast over-ride that limit?

2. What outsider would bother to produce long, random, blasts of radio? Other folks have jobs to do with their radios as well as gov't regulations to obey.

Saying it was from an unstable system is just a fancy way of saying "I dunno. Somepn musta gone wrong."

Subject: RE: Tech: PA goes berserk
From: Mossback
Date: 11 Dec 19 - 12:44 PM

Use hard-wired mics. This & many other related problems solved.

Subject: RE: Tech: PA goes berserk
From: punkfolkrocker
Date: 11 Dec 19 - 01:03 PM

Megaphones.. simpler...

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 11 Dec 19 - 04:44 PM

“Saying it was from an unstable system is just a fancy way of saying "I dunno. Somepn musta gone wrong."”

As I said, it’s impossible to say what went wrong but old equipment gathers dust and grot in its innards. Something as simple as grot on one of the potentiometers can limit sound output and vibration or the equipment heating up can dislodge the dust/grot and result in an increase in volume. Try unplugging all the mics and turn the knobs. If yiu hear a rough sound or crackle they could well need cleaning..

There are a whole host of other potential issues. I turned up at a gig a few years ago and my AER amp refused to output any sound. In discussion with the manufacturer, I discovered that the speaker is wired/switched via the headphone output (i.e. the speaker is supposed to go off when yiu plug the headphones in. I’ve never used it with headphones and there was corrosion in the socket which effectively shorted the speake out hence no sound.

Subject: RE: Tech: PA goes berserk
From: Mossback
Date: 11 Dec 19 - 06:39 PM

Radical Idea: have an electronics/audio tech actually check out the equipment in situ rather than a hail mary pass here??

Just sayin'...........

Subject: RE: Tech: PA goes berserk
From: Mo the caller
Date: 12 Dec 19 - 06:29 AM

It wasn't leeneia's to check / repair. But the more we learn about what might go wrong the more likely we are to cope better next time something does.
Anyway it's fun to swap horror stories.
My best was the gig where my radio mike started misbehaving and a sound man appeared to tell us that in another part of the venue my voice was coming out of Gerry Marsden's guitar amp. So my claim to fame is calling with Gerry and the Pacemakers. Their sound man offered to lend us a plug-in mike but ours smugly told him that we had a spare on a different frequency.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 12 Dec 19 - 09:42 AM

Sound horror stories aren’t confined to musicians. The British Gliding Association used to have an aircraft with an audio attachment to the variometer (the instrument which tells you when you’re going up and when you’re going down). On occasion, this was reported as being able to receive Radio 4.

Unfortunately, cheap, consumer quality, music equipment is often incapable of rejecting radio frequency interference - how many of us remember hearing taxi conversations over the PA in days gone by?

Subject: RE: Tech: PA goes berserk
From: punkfolkrocker
Date: 12 Dec 19 - 10:55 AM

I had a fuzz box that picked up European radio shows...

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 12 Dec 19 - 11:47 AM

Thank you, Mo. It's nice to see that somebody gets the big picture.

And thanks, Ray, for the possible explanations. It's good to feel that something makes sense in the world.

I believe that the callers don't need amplification at all, but I don't suppose they would believe me for an instant. They are 40 years younger than me and are conditioned to sound systems. Probably when they were born, the doctor picked up a microphone and said "It's a girl!"

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 12 Dec 19 - 05:46 PM

You’re welcome leeneia. The main problem with callers is usually that they’re operating in front of the house PA and therefore most susceptible to feedback.

The advantage of modern digital mixinng desks is that they usually come with on-board anti-feedback devices. Try one of these - QSC

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 12 Dec 19 - 06:41 PM

I'll be glad when anti-feedback devices are common.

I just went to Amazon and looked for a book such as "Sound Systems for Dummies". Found nothing. There might have been books that would help the beginner or the interested auditor, but I had no way of knowing which ones. Many of the books were quite expensive, and who knew how technical they were.

I have the feeling that there are simple guidelines to preventing feedback, but so far I haven't found them. At a concert of Irish music with four players, we were hit by feedback 5 or 6 times. I'm convinced the room was so small that no amplification was needed.

Subject: RE: Tech: PA goes berserk
From: EBarnacle
Date: 12 Dec 19 - 11:25 PM

I have external pickups for my concertina. When I first got them I had a problem with cutting in and out after operating for an hour or two. I finally figured out that it only occurred when the batteries were low.

Subject: RE: Tech: PA goes berserk
From: BobL
Date: 13 Dec 19 - 03:38 AM

Leeneia, there's a useful book called "The Country Dance Club Book" which, besides instructions for 100 dances, includes info on dance technique, etiquette, organising events, and - P.A systems. If you can get hold of a copy (it was published privately in England and may not be readily available in the States) it will tell you everything you need to know on the subject.

Subject: RE: Tech: PA goes berserk
From: GUEST
Date: 13 Dec 19 - 03:54 AM

Paul White, tthe Editor of Sound on Sound magazine produced an excellent book on Basic PA usage (not sure of exact title) a few years ago. Possibly available through Amazon.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 13 Dec 19 - 03:57 AM

The problem is, leeneia, that recent times have seen an enormous change in theatre sound and lighting. Old lighting systems have been stripped out and replaced by LEDs and manual sound desks and their associated peripherals (reverb/delay units, compressors, feedback destroyers etc) have/are being replaced by digital.

You will see old lights for sale at excessive prices in antique and “vintage” shops along with second hand manual sound desks at bargain prices in what is left of our music shops. Analogue sound has some advantages over digital but the opposite is also true. The main advantage of digital over analogue is that it is far cheaper and you can do more with it.

Unfortunately, just like the old arguments between satelite tv systems or VHS v Betamax, there is, as yet, no common operational standard. They all do the same thing but in diffrent ways. Mainly for this reason, you won’t find a book which explains everything and, if you do, it will likely be somewhat out of date.

Subject: RE: Tech: PA goes berserk
From: GUEST
Date: 13 Dec 19 - 04:40 AM

On the subject of radio mics, there was the time our ceilidh in a church hall was interrupted by someone coming to tell us that our caller's mic was on the same frequency as the priest conducting mass next door.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 13 Dec 19 - 05:02 AM

Doesn’t have to be a radio mic. We once featured in a review in the Telegraph for a soundcheck! I was sorting the sound for a musical in a large opera theatre whilst the BBC were broadcasting a chamber orchestral concert from the studio theatre next door. Apparently, the main problem was the drums. Not really our problem, you shouldn’t rent out a theatre for a rock musical and expect peace and quiet!

Not quite as funny as a mates ceilidh band which was playing a miners gala in Rotherham. A bloke from next door came in to complain that he could hear the drums over ths sound of his TV. They invited him in, largely to prove that they didn’t have a drummer, but, standing outside, even they could hear drums. Bruce Springsteen was apparently playing in Sheffield five miles down the road!

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 13 Dec 19 - 11:33 AM

Thanks. I'm buying the book by Paul White. I'm hoping that it doesn't matter whether the system is analogue or digital, it's putting out sound waves, and I can learn about sound. If not, then not.

That's troubling about the Springsteen concert. It's too bad when someone can impose for several miles. Maybe i'm being too hard on our callers. Maybe they and the dancers have hearing damage from music like that, and they do need amplification to hear each other.

My uncle's organ used to play the TV from next door.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 13 Dec 19 - 01:13 PM

Paul White is well known but I think his book pre-dates digital mixers. The principles are the same but the way you do things in the digital world is different.

One of the reasons digital mixers are cheaper is because they have fewer knobs - i.e. a knob and a button access umpteen functions rather than everything having its own knob on an analogue system. Ultimately, it can make things a bit harder to do on the fly. If you check out the QSC link I posted above, you’ll find that you can download the instruction manuals which make excellent bedtime reading!

For ultimate on-stage anarchy, have a look at some of the largely knobless souncraft mixers. They generate their own website and, using bluetooth, you can control them with your iPad or iPhone. Not only that but every member of the band can access this on their own device and spend a happy set turning each other up and down!

Subject: RE: Tech: PA goes berserk
From: EBarnacle
Date: 13 Dec 19 - 04:26 PM

Sounds like it would be very vulnerable to being hacked via the Bluetooth interface.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 14 Dec 19 - 03:54 AM

Not sure whether its bluetooth or wi-fi but they are password protected and I can’t really imagine anyone sitting in a concert hall, iPad in hand, with the correct software and advanced knowledge that that particular sound system will be used, purely to disrupt a performance. I’m sure those on stage could make a bigger pigs ear of it themselves! It’s purely down to convenience over risk.

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 14 Dec 19 - 09:58 AM

If it prevents feedback, I'm all for it.

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 14 Dec 19 - 02:48 PM

If it was only that simple! I think you’ll find with digital desks that you need to “destroy” feedback on a chanel by chanel basis. If you sitick one of THESE between your mixer and your power amp, it should Focus in and cut out most of your feedback problems..

Subject: RE: Tech: PA goes berserk
From: punkfolkrocker
Date: 14 Dec 19 - 03:02 PM

It doesn't matter how state of the art a PA is,
or how skilled and qualified technicians are...

It all falls apart into haphazard feedback,
when clueless careless musicians take to the stage,
and ignore all advice where and in what direction to stand,
and not to turn up their instruments above agreed settings...

Then they blame the sound gear and crew...

Subject: RE: Tech: PA goes berserk
From: treewind
Date: 15 Dec 19 - 07:26 PM

What punkfolkrocker said!

(topic drift, though: I don't think feedback was the cause of the problem described in the original post)

Subject: RE: Tech: PA goes berserk
From: GUEST,Ray
Date: 16 Dec 19 - 09:03 AM

May not have been but I doubt whether there’s any other explanation. As I’ve said several times, it’s now impossible to diagnose with any degree of certainty.

Subject: RE: Tech: PA goes berserk
From: GUEST,Captain Swing
Date: 16 Dec 19 - 09:06 PM

I have a hearing aid and recently I went to my local hospital for advice as the device was whistling quite often. The technician explained how the sound would bounce back from, eg wax in the ear and cause the high-pitched sound. He took the device away to check it and as I gazed around the office I noticed on the wall a sign extolling the various services on offer but was astounded to see at the bottom of the page, highlighted and in bold letters:

****** FEEDBACK IS APPRECIATED *******

Subject: RE: Tech: PA goes berserk
From: Big Al Whittle
Date: 16 Dec 19 - 11:34 PM

very interesting...sounds like fun! I alwas enjoy that sort of thing and sorting it out. it doesn't happen much these days as equipment is so much better than it was forty yyears ago.

It used to be that every room was an adventure, every feature in it seemed to unleash its sensitivities.

Subject: RE: Tech: PA goes berserk
From: leeneia
Date: 17 Dec 19 - 04:22 PM

Treewind, I agree it was not feedback. It was static on steroids.

PFR, I also agree about your "clueless and careless musicians" remark. The musicians who hurt me several times were both.