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Double Bass Feedback Problem

H

Harry Horne

May 21, 2002
10
0
93
Near Perth. Western Australia
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#1
Hello from W. Australia! Can your collective wisdom help me solve this problem?
I play jazz using URB with Realist PU through GK MB 150S III plus 100w extension speaker ( Amp normally sits on top of speaker) Amp settings all at 12 o'clock
For 3 years at venue with large platform stage ( no side walls) Perfect sound from amp, no feedback at any volume. Had to move to new venue. Small, shallow stage with brick rear and side walls and roof.
Impossible to use same amp settings as feedback occurs almost at any volume ( even when not playing). Tried with rig in corner, centre stage, close to walls and away from walls. Still have unacceptable feedback. Bring rig downstage, have speaker facing audience and amp facing back, problem is much less but not cured.
Don't believe any fault with amp and am convinced it's the stage/room acoustics. Your help will be much appreciated in solving this . Thanks and regards to all.................Harry
 
#3
wingnut said:
It sounds like the wood may be different. Sometimes I lay a piece of carpet under my cabs and the feedback goes away.
Click to expand...

Thanks Wingnut. The stage floor at the old venue was carpet-covered timber. At the new veue, carpet-covered concrete.
I think I may have to take my gear there and do a thorough sound check and use my EQ to eliminate the troublesome frequencies.
Thanks for your tip
Regards......Harry
 
#6
Harry Horne said:
........ Had to move to new venue. Small, shallow stage with brick rear and side walls and roof.
Click to expand...
Harry that's what is affectionately knows as a "Proscenium Stage". They've been around for centuries and date back to the days of Shakespear before amplification. Back then, the only way they could get the sound to travel to the paying public was to design these stages so they act somewhat like a horn. The sound is designed to bounce off those many, many walls and hopefully project into the crowd.

I say "hopefully" because at low volumes, these stages work well enough. Unfortunately they backfire at anything more that a dull roar. The audio frequencies tend to bounce around the stage, pinging from wall to wall looking for an escape route at the front of the stage. The result, as you know, is very unpredictable. In your case, your pickup is picking up it's own signal a second time around and causing feedback.

Carpet on the floor is a good start, but you need to make sure that all the walls are somehow finished in something equally soft and non-reflective. Thick black curtains on all walls, and especially on that brick back wall, will work wonders.
 
#8
Harry Horne said:
The stage ain't mine to alter.
Click to expand...
Ok so if permanent curtains aren't an option, what about the BYO version. You can bring some black material with you to the gig and stick it to the bricks with gaffa tape. You can then take it down and take it home at the end of the gig. It's more work for you, but I've seen some bands justify the effort but putting the band's logo on the material so it doubles as advertising/branding/marketing.

Otherwise, you'll have to do what the big PA operators do. Option 1 is to get your hands on a 31 band graphic EQ and add it to your rig. Even a cheap one will do. Preferably while the room is stilll empty, slowly raise each slider to see if that particular frequency is "hot" and therefore likely to feedback. If you can raise it most of the way without any feedback, then that frequency isn't a problem and can be put bach to the centre position. If however you slowly raise a slider and you start to hear the onset of feedback, then that frequency is indeed hot......

You'll have to react quickly at this point - quickly lower the slider and cut the feedback squeal off as fast as you can. Prolonged feedback can damage drivers, especially horns and tweeters. Having identified the problem frequency, cut as much of it out as you have to to get rid of the feedback squeal. Once you've done that to all 31 sliders, you should then be able to turn your volume up and/or play feedback free.

Option 2 is the machines that do all of this automatically, but feedback destroyers as yet aren't prefect. They're certainly "quicker" to set up, but most people are able to get better feedback supression with the manual method.
 
#9
There are these foam insulators for pipes (they look like those long skinny tubes little kids use at the pool). You get them at a hardware store. They come in six foot lengths, I stuff them into my bass through the "F" holes. Then take two pieces and cover the holes with them. Then take some plastic tubing (like for aquariums or gas lines) and tightly weave it through the strings between the tail piece and the bridge tightly. Then take some more of that tubing you stuffed into the bass and wedge some between the body of the bass and the tail piece as close to the bottom of the bass as possible. You can also try putting a tennis ball on the end of your endpin. Basically you want to stop as much vibration as possible. A pre amp like the Fishman Platinum EQ will help tremendously. You can PM me with any particulars you need to know and I will help you.
 
#10
Petebass said:
Harry that's what is affectionately knows as a "Proscenium Stage". They've been around for centuries and date back to the days of Shakespear before amplification. Back then, the only way they could get the sound to travel to the paying public was to design these stages so they act somewhat like a horn. The sound is designed to bounce off those many, many walls and hopefully project into the crowd.

I say "hopefully" because at low volumes, these stages work well enough. Unfortunately they backfire at anything more that a dull roar. The audio frequencies tend to bounce around the stage, pinging from wall to wall looking for an escape route at the front of the stage. The result, as you know, is very unpredictable. In your case, your pickup is picking up it's own signal a second time around and causing feedback.
Click to expand...
Durn, that's very interesting.

Have you tried moving your speaker around to various points on stage, looking for a "dead spot"? Don't know if that would solve or maybe at least tame the problem or not.
 
#11
wingnut said:
There are these foam insulators for pipes (they look like those long skinny tubes little kids use at the pool). You get them at a hardware store. They come in six foot lengths, I stuff them into my bass through the "F" holes. Then take two pieces and cover the holes with them. Then take some plastic tubing (like for aquariums or gas lines) and tightly weave it through the strings between the tail piece and the bridge tightly. Then take some more of that tubing you stuffed into the bass and wedge some between the body of the bass and the tail piece as close to the bottom of the bass as possible. You can also try putting a tennis ball on the end of your endpin. Basically you want to stop as much vibration as possible. A pre amp like the Fishman Platinum EQ will help tremendously. You can PM me with any particulars you need to know and I will help you.
Click to expand...
Holy mackerel! I dig the afterlength suggestion. And a phase reversal button somewhere might could be a whole lot easier.

But the rest of those ideas w/ all the tubing inside the bass and f-holes and whatnot makes squeezing the body of the bass between your legs rockabilly-style sound down right conservative. He did say it was a jazz gig, and that his rig sounds fine in other venues.

Heck, what do I know. Never even been to Vegas. Closest I ever got was Reno.
 
#12
Thanks Guys.
I'm now torn between wrapping a cold wet towel round me brow and having a long siesta and taking up the piccolo!!!

I'm going to the venue when it's not being used to see what positioning and amp settings can achieve. We may have to abandon the stage and work from elsewhere in the room.

I'll let you know how I get on.

Thanks for caring.

Sincerely....Harry
 
#13
bolo said:
Holy mackerel! I dig the afterlength suggestion. And a phase reversal button somewhere might could be a whole lot easier.

But the rest of those ideas w/ all the tubing inside the bass and f-holes and whatnot makes squeezing the body of the bass between your legs rockabilly-style sound down right conservative. He did say it was a jazz gig, and that his rig sounds fine in other venues.

Heck, what do I know. Never even been to Vegas. Closest I ever got was Reno.
Click to expand...

Yeah, here in Vegas you can run into some pretty old/cheesy stages. If you play URB in Vegas you pretty much have to do all that stuff I talked about. Between cross frequecy contamination from all the casino radios and internal communication systems and all the external noise coming back to the stage, it's like a freakin' arms race! One of the worst places I played was at a moose lodge with the stage in a cave, the amp was only on two and the feedback was terrible. Even the phase switch on the fishman didn't help. Finally I had to get totally off the stage and stand to one side just to stop the feedback! Don't even get me started on kwanset huts!!! :rollno:
 
#14
Had horrible feedback a couple of weeks ago. Went out and bought the Fishman Pro-EQ Platinum Bass Preamp, Equalizer and DI. I am using the Revolution II that I bought through Upton Bass. It was able to dial out all of the feedback and dial in some decent low end too.

I also added a Shure Beta 57 mic to the mix copying Chris Fitzgeralds rig (sort of) and ran that through the mic channel on my AI Clarus II:
http://www.talkbass.com/forum/showthread.php?t=254667&page=2&highlight=shure+beta+57
I used this new kind of velcro strip to hook it up, and in the process I also put a couple of strip around the strings behind the bridge to hold up the back of the shure. This helped with the feedback too I'm sure. Would have added the foam as per wingnuts suggestion but time ran out. "All hail, wingnut", king of feedback lore.
 
#15
You should see my poor bass, looks more like a science project gone wrong than an upright! I even squirted some of that foam sealant stuff into the bottm left side of the bass. That helps out with the "squeeze with your thighs" thing! I also tried some of those string dampners used on compound bows (the kind you shoot) to help, but they fly off the strings...it's pretty funny to watch the reaction of the crowd when what looks like a big black fuzzy spider lands in your cleavage!
 
#16
wingnut said:
You should see my poor bass, looks more like a science project gone wrong than an upright! I even squirted some of that foam sealant stuff into the bottm left side of the bass. That helps out with the "squeeze with your thighs" thing! I also tried some of those string dampners used on compound bows (the kind you shoot) to help, but they fly off the strings...it's pretty funny to watch the reaction of the crowd when what looks like a big black fuzzy spider lands in your cleavage!
Click to expand...
Wingnut you know how it works on the internet - if there's no pictures, then it doesn't exist :)

Have you got a pic or two you can share?
 

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