Hollow body trouble

[Tony Wonder]

Hey folks,

I'm pretty new to playing hollow bodies. I have been working with the Eastwood Classic 4 (i love it.), but every once in a while, depending on the room, I will have feedback issues. (Not related to stage volume of MY amp, because I keep it low and off stage usually. However pretty much any other sound from the PA or sound system will set it off, (snare hit, vocal mic, etc.) like i said this RARELY happens, but when it does, I have to ditch the bass for the entire evening. Which I hate to do.

So, what is the consensus for problems like this? New pickups? If so, whats a good pickup to go for?

(This may have been covered somewhere before. I often come to this site, but Ive never posted. Be gentle.)
Thanks for reading.

[Turnaround]

There are a number of situations that can contribute to feedback. The first is the nature of the hollowbody instrument. Any sound source that is near the resonant frequency, multiples or partials thereof, can induce feedback. That's just the way it is. Be glad you're not a double bass player - they get the problem a lot.

Pickups that are microphonic tend to make the situation worse. So replacing your pickups might help to some degree. Or you could have the existing pickups potted to reduce microphonics. If you don't know what I'm talking about, best consult a qualified technician.

And you might investigate the use of a phase inversion circuit. It works by cancelling out the problem frequency. Trouble is, it is likely to introduce the problem at a different frequency.

Good luck. It's not an easy problem to solve.

[Tony Wonder]

Very helpful, thank you! I appreciate it!

[Stilettoprefer]

Watch where you stand! I play double bass and feedback is a b**ch. If you're near a monitor, feedback becomes a problem quickly, so avoid standing directly in front of them at all cost!

And as said above, microphonic pickups are a problem too. my thinline tele seems to have that problem (oh well, it needs new pups anyways:P)

But watching your placement on stage is crucial when using hollowbodied instruments.

[mpdd]

i have heard that people fill the body with foam to reduce feedback, but that seems strange, because it wouldn't be hollow anymore if it was filled

[Pilgrim]

Feedback is an acoustic and mechanical interaction with soundwaves.

You make soundwaves - they hit the body of the instrument - causing the instrument to vibrate - which puts those sound waves back into the output of the instrument. Sound waves also enter through the F-holes and bounce around inside the instrument, adding to the general fun and frivolity. A big part of the issue here is that the hollow body provides an acoustically live "box" with hard sides, which is a perfect place for sound waves to bounce around.

Ideas:
- Don't stand in the path of the sound waves - meaning don't stand in front of your speaker.
- Move the speaker to another spot on the stage, away from you.
- If there is one specific frequency which makes this worse, attenuate that frequency on your amp head.
- I've never tried it, but you can try putting clear tape over the F-holes...that should reduce the influence of having an open passage into the body of the instrument. You might also try some foam rubber painted black and cut slightly larger than the F-holes that you could insert into them.
- Insert poly fill or some other material through the F-holes to reduce sound wave bounce inside the body of the instrument.

Many manufacturers sell rubber plugs for acoustic guitars and basses which mostly block the center soundhole on their top surface. That's why I suggested the tape idea. Be careful with your finish.

[Tony Wonder]

Originally Posted by Stilettoprefer

Watch where you stand! I play double bass and feedback is a b**ch. If you're near a monitor, feedback becomes a problem quickly, so avoid standing directly in front of them at all cost!

And as said above, microphonic pickups are a problem too. my thinline tele seems to have that problem (oh well, it needs new pups anyways:P)

But watching your placement on stage is crucial when using hollowbodied instruments.

For sure, That's also a weird factor, because we don't use stage monitors, so any triggering sound is strictly coming from the house PA out to the audience.

[Tony Wonder]

Originally Posted by Pilgrim

Feedback is an acoustic and mechanical interaction with soundwaves.

You make soundwaves - they hit the body of the instrument - causing the instrument to vibrate - which puts those sound waves back into the output of the instrument. Sound waves also enter through the F-holes and bounce around inside the instrument, adding to the general fun and frivolity. A big part of the issue here is that the hollow body provides an acoustically live "box" with hard sides, which is a perfect place for sound waves to bounce around.

Ideas:
- Don't stand in the path of the sound waves - meaning don't stand in front of your speaker.
- Move the speaker to another spot on the stage, away from you.
- If there is one specific frequency which makes this worse, attenuate that frequency on your amp head.
- I've never tried it, but you can try putting clear tape over the F-holes...that should reduce the influence of having an open passage into the body of the instrument. You might also try some foam rubber painted black and cut slightly larger than the F-holes that you could insert into them.
- Insert poly fill or some other material through the F-holes to reduce sound wave bounce inside the body of the instrument.

Many manufacturers sell rubber plugs for acoustic guitars and basses which mostly block the center soundhole on their top surface. That's why I suggested the tape idea. Be careful with your finish.

I haven't tried adjusting my amp frequency yet, but I have tried putting foam in the F-holes. It seemed to work great, but then some days it would act up again, I was thinking a more dense foam would help, like Neoprene, but Im just guessing. I don't really know if that would make a difference or not.

[AltGrendel]

I've read that Steve Howe doesn't use foam or any of that stuff on his ES-175. I seem to recall that he said that he uses his body to dampen the effect, holding it tighter to prevent the resonation from starting.