Official Luthiers Forum!

Hey guys

I need some advice on tracking down a buzz on a closed box. I am hesitant to do any more until I get this sorted out.

The buzz sounds out when tapping the top but not noticeably when I tap the back. It's also not noticeable when my hand is in the sound hole.

Ideas on how to track it down.

Thanks
John

Put back down on padded surface. Tap over the bracing pattern. Usually, anything loose will make a snare drummy sound...

If you are using reversed linings on the top check for any breaks at the kerf. This is hard to do with the box assembled, I had this happen to me with just top installed. A lot of pulled hair on the floor before I figured it out. A drop or two of CA glue and it was cured. Hope you find it, these can be very trying.
Tom

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A person who has never made a mistake has never made anything!!!

Have you installed the bindings?
If not cut the channels & look for any gaps between the linings@ top glue
joint & the back glue joint .
Do your back &some top braces go into the linings !
Cut in that is!
Tapping(light tapping with a finger touch) can sometimes locate the suspected area .

Mike

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Mike Collins

More information would be helpful....

What kind of guitar is it?
Is it something that you built?
Age?
Other obvious issues such as bridge pins not wanting to seat all of the way?
Anything else that does not look right?
Are the fret ends sharp indicative of the thing having been left to dry out at some point?
If it's one you are building is the bridge on yet and if so was the bridge gluing caul removed? Don't laugh I've done this and man did it sound better when I removed the caul...

By buzz be more specific please? Some buzzes sound obviously metallic, some do not, what ever else you can add.

One possibility when we are shooting in the dark here as mentioned is a loose brace or brace end. As JF said the drum sound or rattle when tapping tracing the bracing pattern.

If you let us know what kind of guitar it is we can tell you in our experience where they are known to fail.

Any fairly large shell pieces in the rosette? I had a box buzz once, which I think was due to an inlay losing part of its glue joint, but not enough to actually come loose. It would only rattle when tapping pretty hard, which meant that there was too much sound reverberating around the whole thing to get an accurate position on it by ear. Definitely one of the most annoying kind of problems to track down in guitar building.

I am trying to tie up a build that has been on a 3 year hiatus with me.

The box is closed and bound. No bridge, no neck. It has a wash coat of nitro on it to protect from dings.

Seems that now I remember it had a buzz after I closed the box ..... So it's not like this is s new development due to 3 years of moving around.

There was no buzz on the top bracing before I closed the box. There is a possibility that the buzz is coming from the back - as the wood was severely bug eaten. I filled all the holes I could find with epoxy. I hate to rip the back off to find out - but that may be needed. Unfortunately, the back is quite unique - I won't be able to find a match.

I know it's flying blind - but I was hoping for suggestions on how to track down whether the buzz is from the top, back, linings, etc.

Thanks

Stethoscope and judicious tapping. It could be anything at this point based on what we know.

A challenge indeed. Since this is a new build I will assume for the time being that it's not coming from the braces as those were glued
out in the open with proper clamping. I would guess, that's all it can be that during the process of cutting the binding channels
you inadvertently caused the buzzer, most likely somewhere in the lower bout. Usually a buzz won't show until after string up. I'm up
for a challenge so here is what I would try. Attach a handle, holding device, where the neck would bolt, then clamp the handle to a bench or something with the guitar overhanging. This leaves the guitar suspended and both hands free. Make a slightly curved (so that you can reach inside and touch the lining area in all places) stick a couple feet long and attach a small piece of foam or something to one end. While inducing the buzz (even better a if helper did this) reach inside and methodically probe around. If you suddenly deaden the buzz, Bingo! Bob's your uncle. I know this is a simplistic approach and you may have already tried it but this is where I would start.
You may eventually find the source of the problem by finding where it's not. You'll find it.
Ken

So... I rooted around with a mirror and a flash light and felt all around - and it was buzzing... then it stopped... but I didn't actually do/fix anything...

grrr...

but when it was buzzing - there was a particular position with the mirror laying on the back where I could start and stop the buzz... I think I have a problem with this back... Probably one of the semi-stabilized bug tracks is a little loose.... grumble grumble...

I guess it's time to go buy a new bottle of super-thin superglue.....

Thanks