Strange problem with bass rig at a gig last night

[wesg]

The bass guitar volume kept creeping up and then really got LOUD. Bass player swears he never touched a thing and he was actually the one complaining most about the volume. We had bass in the rear monitor (JRX 112), my monitor (NX55P w/o HPF) and a bit of bass coming out of the bass amp. The bass amp was definitely quite quiet at sound check. I know the knob didn't creep on the bass, because the bassist told me he sound checked with knob up full blast and left it there most of the night, except when playing with a pick, he would turn it down.

 

The bass volume creep was not minor. It was MAJOR. It got so bad I could feel it throbbing my chest and vibrating the stage (sound guy was trying to pick up chicks, I had to hop off stage and tell him WTF?!). It was coming from everywhere -- subs, monitors, I don't know about the bass amp. Sound guy said the signal was way hotter than earlier in the night, he pulled the input trim way down on the board. Stage volume was pretty reasonable otherwise for a rock band, my Leslie 760 was easy to hear without being run full-out.

 

Possible clue: a few times throughout the night there were loud pops in the sound system, not sure which speakers they came from. Sound guy claims he never heard them come through the FOH system.

 

Bass player can't understand what happened. His two theories are that the battery in his bass was dying, or that the amp doesn't work right at low volumes after a while. I don't buy either of those. He's a talented player but quite new to the scene.

 

My theory is that maybe there was a loose or faulty cable between the bass and the board, that started making a proper connection somehow.

 

Any suggestions for further investigation?

 

FOH - 2 x PRX 515, 2 x PRX 618S in a corner. Subs run from "mono out", mains high-passed.

Monitors - JRX 112 (two front, one rear), plus NX55P at keys position

Desk - Mackie Onyx 24-4 at the end of a hundred foot snake

Bass - something newish with active pickups and a Mark Bass amp with a matching 2x10 + tweeter cab. Balanced out from amp plugged into snake.

 

Thanks,

Wes

[agedhorse]

What bass amp was it? Was the volume change through the bass amp or FOH or both?

[wesg]

Hi, Andy;

 

I'm 99.9% sure the amp is the Little Mark III and the cabinet is the Standard 102 HF (both Mark Bass).

 

The volume change was definitely through the FOH, I could feel the subs and still hear the loud bass when I left the stage. I cannot say with certainty if the bass's volume increased at the amp or not, as I was getting so much from the subs that I'm not sure if I could have heard the bass amp. That said, the drummer - who was sitting right next to the bass amp - said it was so loud he hurt his ear (badly enough to consider consulting a physician - he could not hear properly for the 3rd set and the pain did not go away).

 

Thanks,

Wes

[WynnD]

If the bass was DI'd out pre fader and eq, there shouldn't have been any changes at the sound board. Obviously that wasn't the case. That's one reason I love the Hartke Kickback. The DI bypasses all the amp's controls. Changes on the amp only occur locally. That said, things like this happen and everyone needs to be aware when it occurs. Personally I hate too much bass. It muddies the entire sound. And a 760 Leslie is about 118 db max at 3 feet. (At least mine is. I hate mic'ing them.)

[agedhorse]

Wynn, this is not entirely true. We still haven't determined if the problem was in the amp or possibly within the bass itself. If the problem was in the bass, the pre output would reflect the problem as well. This is the reason why I asked if the volume difference was also at the bass amp, to help eliminate a possible problem within the PA itself.

 

Your personal preferences regarding levels have no business being brought up here... there was a problem that had nothing to do with how something should have been working as it was not working correctly.

[wesg]

Thinking back on this. I recall at that at its worst the whole stage was shaking, I could feel it through my organ bench. Could subs six feet from the stage make the stage shake like that, or it would it have to be the bass cabinet ON the stage? The stage was about 12 x 9 feet, 15" tall, covered it carpet and presumably hollow.

 

I'm asking this as I'm trying to use details in my recollections to guide my understanding of what component in the chain caused this. No chance of figuring out which amp->snake cord it was, but I'll get the bass player to let me examine his patch cable at least.

[Art Flood]

Wes,

 

I had a similar problem at a recent gig in a room I had worked in without problem on several occassions. I had been warned that it was a difficult room with a very low ceiling over the stage area but which opened up into an area with a very high ceiling.

 

No problem in the first set, but in the second set everytime the bass player played a note on the low E string ( below about A) the room would shake. I was leaning against a air hockey table that was covered by a piece of particle board and it would vibrate like a small earthquake (it was probably 30 feet from the bass player and 15 from the guitarist). As I didn't have bass or guitar in the PA (they were both loud enough to carry the room) there was nothing much I could do other than ask the guitar and bass player to turn down. They were reluctant to do so as they couldn't hear any problems but eventually did and the problem went away.

 

I believe it was some sort of room resonance. I suspect there was a gradual increase in volume particulary from the guitar and bass player and eventually we hit the point where certain low frequencies become resonant. Note that although they were louder than I would have liked, they were not all that excessive. Patrons were still enjoying the show and there were plenty of dancers.

 

The resonance was really only in one part of the venue (and it was under the low ceiling) and easy to find as the patrons just moved away from there. At first I thought it was the guitarist, as he was using a quad box for the first time and the problem would dissappear when he played a solo but came back when he started chugging on chords. I was probably a combination of bass and guitar - the bass player often has a very muddy bottom and possibly no idea of this or how to fix it.

 

Could you have had a similar problem. It doesn't really sound like a bad lead problem to me.

 

Cheers

 

 

[wesg]

Hi, Art!

 

That's an interesting hypothesis.. I don't *think* this is the situation in this case, though.. the room is quite regularly shaped and is very high, even acoustically-treated. The vibration through the stage was also continuous and spanned a couple of songs.

 

I'm really scratching my head on this one. The drummer thinks the loudness that was bothering him most was coming through the JRX 112M near him, maybe just the string-pluck transients? IIRC The JRX was sitting right on top of the bass cabinet, though. So maybe both.

 

I don't have a lot of information to go on, but I would really like to solve this problem before it happens again. The drummer heard back from his audiologist, he definitely lost a chunk of his hearing that night, this is no joke. He is a recently-retired factory worker and so has had annual hearing tests since 1991 to establish a solid baseline.

 

Wes

[RoadRanger]

The drummer heard back from his audiologist, he definitely lost a chunk of his hearing that night, this is no joke.

Who set the limiter on the monitor that loud?

 

[Shaster]

Assuming it wasn't the bass itself, it might have been a pad, either on a DI or the board, that got hit on a break and the tech did not respond to the new level properly. He might have just thought, wow the bass is a lot louder, and not investigated further.

 

I also first thought it was bass through the kick drum mic syndrom, but looking closely at the way it's been described, I think not.

[wesg]

"Who set the limiter that loud" - nobody providing sound at my level uses limiters around here. I wouldn't personally know what to do one, either....which is one reason why, when providing, I only use powered speakers. It's not fool proof but at least output is a known quantity.

 

In this case, the JRX112M was being driven by wide-open Crown class-D amp rated, I believe at 440W/side. No clue how much SPL that can generate. IF it was high-passed it would have been at 50Hz.

 

Shaster - interesting theory. There was no DI, but the mixer does have a pad button. It hasn't been used since the show...I'll be checking tonight.

[RoadRanger]

In this case, the JRX112M was being driven by wide-open Crown class-D amp rated, I believe at 440W/side. No clue how much SPL that can generate. IF it was high-passed it would have been at 50Hz.

Yah, them JRX can get pretty harsh IME. I have IPR1600s on my monitors that self limit at 300w - I'd prefer that they were 200w, shoulda used Crown XLS1000's. Last night I had my rig out with a band I was filling in on bass with - their monitors are JRX and they noted how much better mine sounded .