Feedback at a show. Only guitars effected?

[blindboybenton]

Hi All

Ive just come back from a show where there was 2 bands playing. Mine and another
while sound checking the guitarist of the other band was having troubles with feedback and very low vol. we tried everything and in the end he moved to the other
side of the stage and.. we had the same. Switched off the lights/PA and tried different guitars. He was using a Hughes and kettner head amp with 4 x12" ( OTT for this type of show ). I put it down to the amp
he didnt, In fact he got very upset by this lol

My guitarist turned up with a Fender Princeton, - feedback at Low volume . He drove home and got his Roland Cube 60 - feedback at Low volume

Both guitarists went into the pa - feedback at Low volume, But slightly better. So they all used the pa,

Myself and the other bassist using solid state amps. Not a problem

What the hell was causing that ?

bassman1965

[wizard333]

Were you mic'd up when the feedback was occurring at very low volume? I'd suspect a feedback loop somewhere in the PA, since that was the only variable held constant. Most "sound men" are guys who smoke the most pot with the bar owner, not people who know wtf they are doing.

[blindboybenton]

this is with just a guitar straight into the amp. no effects not going into the pa. was not reqd

[R.G.]

Was the PA *turned on* and *microphone* hot? If so, it was going into the PA.

[mikeboone]

Were the guitars in the monitors? Side fills? Guitars are tricky in the monitors. I find the frequencies the "pot heads" are trying the eliminate from the monitor mix to keep it from ringing are where a guitar sounds best, just a theory. I keep my amp volume a smidge louder than the snare but not as loud as a crash cymbal and never ask for guitar in the monitor. It gives me good stage volume without killing anyone and the "pot heads" don't bother with me. Its easy in a club. Not so much outdoors.

[Enzo]

Simple test. regardless of whether the amps are connected to it, stand there on stage, get the feedback happening, then TURN OFF the PA and see if it stops or continues.

[blindboybenton]

Hi
This was with the PA turned off. Nobody was connected to it apart from the vocals. The lights turned off and the DJ sound kit turned off

When i say low volume i mean very low.

[Chuck H]

So, to crystalize this. No PA or monitors were on at all. There were absolutely no variables other than the room. These guitar players have no trouble with these amps and guitars in any other room. Is this correct?

[Brad1]

Bassman,

Let me preface by saying I'm not accusing you of being un-knowledgeable about anything, but more details may help narrow this phenomena down.

Two statements by you:

"My guitarist turned up with a Fender Princeton, - feedback at Low volume . He drove home and got his Roland Cube 60 - feedback at Low volume"

"Myself and the other bassist using solid state amps. Not a problem"

That last statement rules out it being ONLY tube guitar amps, because a Roland Cube is SS.

You state that it's ONLY the guitar amps doing this, and NOTHING else is on...no PA, nothing. And, it's doing it at low volumes.

Are you sure you are describing "feedback" properly? Feedback is when a signal regenerates itself by being picked up by a microphone or instrument pickup and fed back through an amp/speaker at a level that allows the amplified signal to picked up again by a mic/pickup, fed back through, etc. It can be a squealing, piercing high-pitched sound, like mics tend to do...or it can be at certain frequencies that resonate, say, guitar bodies to vibrate pickups. Sometimes, you can control the feedback for effect. Think Ted Nugent "Stranglehold".

It takes a signal strong enough to overcome distance to make a guitar feed back.

Solid body guitars are less prone, but can be induced into controlled, or uncontrolled, feedback by being loud enough, and moving closer to a speaker with the pickup and front of the guitar facing the speaker.

Many semi-hollow electrics are more prone to feedback, just because their open bodies vibrate more easily, and pass those vibrations along to the pickup.

Acoustic-electrics are even more prone because they are even more easily induced into vibrating, given they generally don't even have a pickup mounted on a center block inside the body, like many semi-hollow electrics. They may have piezo or microphone pickups that are very easily driven into feedback.

So, what kind of guitars are being used? If they are solid-body electrics, and you don't have the guitars' pickups just a couple inches from a low-level amp...it's extremely unlikely that the guitars are "feeding back".

Also, feedback will occur at at any frequency, depending on the strength of the inducing signal and the resonant acoustic properties and frequency ranges of the object picking up the feedback.

Are you sure you are not referring to some kind of "interference"?

Is the noise always the same frequency? Is it high-pitched and squealing? Does the pitch and level change as you move to and from the amp? Is it a buzz? A 60Hz (or some equal multiplier, such as 120Hz) hum?

Has anyone checked out the voltage from the outlets to see if it is in a reasonable operating range for the equipment?

What else is ran on the same building circuit? The beer cooler? The entire kitchen?

Are there a dozen neon signs lit up and flashing around the playing area, and do they constantly have a bunch of fluorescent lighting on?

Are you, perhaps, picking up some outside radio frequencies from some nearby transmitter?

Are you using good quality "instrument" cables from guitar to effects/amp, and, possibly, good "speaker" cable from amp to speaker?

Are you using wireless guitar packs? If so, what are the operating ranges? If using something older that the FCC has prohibited, are you possibly picking up Eric Holder's bugging signals that he's trying to use to shut down the owner because he's conservative? (Sorry...couldn't help it! They just give us so MUCH to work with!)

Does all the equipment work normally elsewhere, louder and no...whatever you're hearing?

Are you entirely sure it's "feedback", and not "interference" or something else?

Describe the sound, as well as you can. It's hard to believe a low-level amp will cause feedback through a normal guitar of reasonable quality, from a few feet or more away. (Although, I did used to have a cheezy Kingston hollowbody electric that got dubbed "Feedback King" because of it's amazing ability to feedback at ANY usable level...if you weren't turned just right!)

More info may yield a better explanation.

Brad1

[Steve Conner]

Most likely explanation is that the PA wasn't turned off when you thought it was. Other than that, maybe demonic possession?

[Chuck H]

I'm thinking it wasn't actually feedback. But rather some interference. A ham or CB guy with a signal going or something. The question about "same frequency" is a good one. In this case, the reason the bassists didn't have any trouble could be that the guitarists were using so much more gain.

[eschertron]

I was at a gig once where the trumpet player showed up with a MIDI trumpet controller. He'd stand to the side and play this extremely high pitch, modulating it louder and softer with his controller. Sound guy thought it was a microphone feeding back. Drove him crazy.

...maybe it's the same sound guy, snapped and lurking at shows to drive unsuspecting guitarists crazy.

[R.G.]

Most likely explanation is that the PA wasn't turned off when you thought it was. Other than that, maybe demonic possession?

I'd go with that. The building was possessed by Maxwell's Demon.



The PA was not off, and all microphones were not off; OP sez:
This was with the PA turned off. Nobody was connected to it apart from the vocals.

Everything oscillates if you put enough gain into it. What stops oscillation is either lowering gain or increasing the attenuation of the feedback path so the loop gain gets under 1.

It would have been a very interesting thing to pull the plug out of one of the guitars and see if the squeal ceased. If it did, the feedback was coming through the guitar. If no, the problem was feedback into the amps.

It's interesting that the squeal seemed to quit with physical movement (I *think* that's what was meant by moved to the other end of the stage). This could match there being an acoustic focus point on the stage, or and electronic source of interference that was local to that place, perhaps as mentioned RF, or some appliance in the building emitting stuff that was picked up. Guitar pickups work well on emitted fields, and the switching power supplies of many electronic things now emit M-fields. In both these cases, moving the guitar and/or amp to another location moved it from the point of high feedback signal to lower feedback signal.

Buildings sometimes have funny interactions with high gain guitar amps. Building wiring these days is often used for sending signals, such as X-10 control signals, ethernet signaling, even telephone signals. This is the form of possession by Maxwell's Demon I was thinking of. But an appliance or device with a switching power supply or such may have been tucked under the stage as well.

This is all going to be speculation without more testing on that specific stage without the time pressure of a show.

[big_teee]

Sounds like a Telecaster Bridge pickup with a loose microphonic baseplate on the Pickup?
T

[soundguruman]

Hi All

Ive just come back from a show where there was 2 bands playing. Mine and another
while sound checking the guitarist of the other band was having troubles with feedback and very low vol. we tried everything and in the end he moved to the other
side of the stage and.. we had the same. Switched off the lights/PA and tried different guitars. He was using a Hughes and kettner head amp with 4 x12" ( OTT for this type of show ). I put it down to the amp
he didnt, In fact he got very upset by this lol

My guitarist turned up with a Fender Princeton, - feedback at Low volume . He drove home and got his Roland Cube 60 - feedback at Low volume

Both guitarists went into the pa - feedback at Low volume, But slightly better. So they all used the pa,

Myself and the other bassist using solid state amps. Not a problem

What the hell was causing that ?

bassman1965

A common problem is mechanical reverb in the PA. These type reverbs use a long spring...
The vibration from anything on the stage (drums, bass, guitar) starts the spring moving, and it rings like feedback.

Cheap PA systems do not control the reverb return, only the reverb send. The return of the reverb is always on.
There is no way to turn the reverb return down to a lower level.
The only way to shut it off is to plug in the reverb foot switch, and click OFF. Then it finally stops.

The mysterious ringing is this type of cheap-o reverb return problem. Only junk cheap PAs (like crate, etc...) have no reverb return level control. Another one without a reverb return level control is Kustom, another one is Centaur...

Putting spring reverb in a PA mixer is pretty idiotic to beguine with. It sounds horrible, and causes all kinds of feedback and vibration related problems with sound systems. It's stupid, and shows just how "out of touch" manufacturers are, with professional sound system design. Using spring reverb, without a return level control is moronic.

The only type of effects that have any business being used, in a pro sound system, is analog or digital, electronic effects, with no mechanical dependent spring, tape loop, etc...This is your problem.

TEST: turn the reverb down to zero. Shake the amp, do you hear the reverb spring banging around?
If yes,YOU have an amp without a reverb return contol. Now you know where the ringing is coming from.

Professional mixers and amps (like a Fender) ALL have a reverb control, that shuts off the reverb return.

Another cause is that there is no EQ on the PA system. The EQ is used to notch out resonant frequencies. A 31 band, 1/3 octave EQ is the professional standard. If you don't have a 1/3 octave EQ, constant ringing and feedback is a GIVEN in PA systems.