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Weird cab behavior at gig last night

mrcbass

mrcbass

Jan 14, 2016
4,425
13,029
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Sacramento, CA
#1
So this feel like a stupid question, but I'm a bit confused about my experience.

I was playing a gig with FOH support last night. My cab was just for stage volume (didn't really even need it) but not the issue. About half way through the second set, my cab started farting really bad - I was sure i had blown a speaker. It was a bit intermittent, but I was very glad that it wasn't coming through FOH. The issues continued into the third set. (Issue aside, it was very odd playing a highly distorted sound on Tennessee Whisky.)

Got through the gig, got hoe this morning and tried to trouble shoot. I cannot reproduce the problem at home. I opened the cab (Markbass P210 Traveler 4ohm) and tried to feel for cone tears; none are found. I noticed that my preamp gain had got moved up a lot so I took a bit of relief that I was just severely over driving the amp. Set every thing up and tried to make it fail. I could not. I tried maxing out the preamp gain and brought the amp to 100 % (the preamp was at about 80% and I was running at about 30% on the amp (GK Legacy 1200) at the gig). I finally got some ugliness when I started boosting the trim on the amp, but still not farting sound I experienced last night.

The two notable things about last night:
1. FOH support. I've played maybe 15 gigs with FOH support. I have experienced odd behavior before at one other venue, but have played their many times and the issue was more of an amp fail than distortion. I chalked it up to bad power supply when a tech type buddy, couldn't find any issues the following week. I have played this venue before, but I'm pretty sure, it was a different sound system.

2. The second notable thing about this gig was the heat. we were outside, about 108* at load in and my gear had been in my car all day, parked in the sun. Last night I was thinking that perhaps the heat had done something to the glue on the cones, so I was surprised that I found no sign of failure.

Now I'm thinking that the FOH was somehow feeding something back into my amp. (Yeah I know, this is the stupid question part.) I don't know the brand or pretty much anything about the board except that it looked pretty sophisticated. I was watching the sound guy se tup the drummer and noticed that the board had a digital EQ display that the tech was modifying. Not for nothing, there were two board in play - there was another mixer on stage that another tech was using to manage our monitor settings. No idea if this has anything to do with anything, just adding as much detail as I can remember.

Ay ideas what would cause tis type of issue?
 
#2
You may have been hearing something loose or vibrating on the back of the mains or subs. It may not have been very audible at FOH, but you would probably hear it pretty well behind them. It also could have been a sympathetic vibration something else in the room or in the area. We used to play in this place that though corrugated sheet metal was good design choice. Third fret G would set that stuff in motion and it sounded like the place was going to fall down. Couldn't really hear it our front.
 
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#6
Heat compression in the coils?

Keep in mind also that knob positions on an integrated amp (compare to a different brand/model power amp) DO NOT correspond to % of power fed to your rig. Matter of fact knob positions only give you a reference of where you left off last time in TONE. Never try and use knob positions as a guage in how much power you're feeding your cabs.

Unless you tried to reproduce the symptoms with the EXACT rig, you can't "figure" how much power you were feeding the cabs.

My hypothesis here is heat and power output just took its toll on your cab, and being 4 ohm, you simply had a little too much mustard on your rig sandwich.
 
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#9
trevcda said:
You may have been hearing something loose or vibrating on the back of the mains or subs. It may not have been very audible at FOH, but you would probably hear it pretty well behind them. It also could have been a sympathetic vibration something else in the room or in the area. We used to play in this place that though corrugated sheet metal was good design choice. Third fret G would set that stuff in motion and it sounded like the place was going to fall down. Couldn't really hear it our front.
Click to expand...
Thanks, but no it was at my cab - had to get right in front of it to really hear it was from my rig.
 
#13
A standard "power conditioner" won't help low line voltage but can cause problems depending on how it's designed.

A voltage regulating "power conditioner" can also cause problems with highly dynamic loads if the control loop is too slow or (especially) too fast.

Try without the power conditioner (the amp has all the conditioning it needs built in) and also try bypassing the effects loop with a 1/4" jumper cable. The loop switch may not be fully closed.
 
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#15
mrcbass said:
Thanks, but no it was at my cab - had to get right in front of it to really hear it was from my rig.
Click to expand...
It could have been your cab that was rattling on the stage, or something was slightly touching your cab and rattling, or the stage floor directly under your cab was loose and rattling. Not saying it WAS this. But very well could have been sympathetic vibration from your cab, or something touching it, or in its immediate area to sound like it was your cab. Especially since you couldn't reproduce the issue at home. Especially if it was intermittent. Certain frequencies resonated more with whatever was rattling and farting on stage.

A loose or corroded connection could also be the issue. Could be anywhere from the bass, through your signal chain, to the amp.

It probably had nothing to do with the PA system doing something to your amp. The FOH, monitors, and their corresponding mixers wouldn't be sending something back to your amp. There is the possibility, if you plugged into a DI box for the PA, and then from the DI to your amp, that the DI had a loose or corroded connection on it, or the cable between the DI and your amp.

Another experiment to see if there's something loose or corroded is to move your gear around. You don't have to be violent with it. Just regular lifting, moving, and putting down. Try moving your amp & pedals to different locations in your home or practice room or wherever. Plug in and see if it happens. Move and try again. Sometimes our gear works fine until we move it to a gig and that loose connection shakes looser and an issue develops. And you move it again and it shakes back to make a connection or the cables drape just the right way to create tension on the contact and it magically gets better for a while. Moving the gear around could jostle it just enough to shake whatever loose again. It's a longshot and a PITA to try, but if you're so inclined.

(My bet's still on sympathetic rattling in the immediate vicinity of your amp on stage. But i wasn't there to hear it.)
 
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#17
MrLenny1 said:
I had a few gigs where the FOH was so loud I could not hear my amp on stage.
I kept turning up the amp to the point of distortion.
Click to expand...
A good reason not to have more power than the cabinet can safely handle. If you can’t hear well, you also can’t hear the speaker destroying itself in the process.
 
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#18
trevcda said:
You may have been hearing something loose or vibrating on the back of the mains or subs. It may not have been very audible at FOH, but you would probably hear it pretty well behind them. It also could have been a sympathetic vibration something else in the room or in the area. We used to play in this place that though corrugated sheet metal was good design choice. Third fret G would set that stuff in motion and it sounded like the place was going to fall down. Couldn't really hear it our front.
Click to expand...


Had this very thing going on at last night's job.

Outdoor festival, furnished sound company and crew with a large, portable aluminum stage, flown FOH system with subs stacked on ground on each front corner of stage.

Every hit of the bass drum, anything coming from my little 210 bass cab in conjunction with those subs absolutely swamped the stage and shook anything not fastened down.

We/they did eventually get it all sorted out and things sounded great.
 
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#19
So another thought. Again seems unlikely, but no luck with any other exploration to date. I was using wireless. Usually, it's the only wireless device in use (on stage), but the sound guys provided wireless vocal mics. Normally, when my wireless doesn't like a venue, it's just a little scratchy and it happens right away, never as severe as this was and never delayed. But perhaps with 4 other wireless signals, something got amplified? Doesn't explain why it wasn't an issue in first set though. Maybe the fireworks folks had some sort of wireless triggers that were messing with me? It did get worse the closer we got to the fireworks schedule. Hopefully today's gig will give me some sort of closure.
 
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#20
mrcbass said:
So another thought. Again seems unlikely, but no luck with any other exploration to date. I was using wireless. Usually, it's the only wireless device in use (on stage), but the sound guys provided wireless vocal mics. Normally, when my wireless doesn't like a venue, it's just a little scratchy and it happens right away, never as severe as this was and never delayed. But perhaps with 4 other wireless signals, something got amplified? Doesn't explain why it wasn't an issue in first set though. Maybe the fireworks folks had some sort of wireless triggers that were messing with me? It did get worse the closer we got to the fireworks schedule. Hopefully today's gig will give me some sort of closure.
Click to expand...
That's certainly another possibility. Whenever you are having unexplained problems, simplify all the way down to the very basics to exclude as many possible causes as possible.
 
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