Double Bass Why is my bass "knocking!?"

[burns_isaac]

Ok so yesterday my new "used" bass started a new buzzing sound around the tailpiece, bridge, sound post area and today after tuning up and doing some bow exercises, I moved onto some pizz stuff, as usual, and along with my first strong pizz came a very loud and at the same pitch "knocking" sound like something is banging around inside my bass at near the same pitch as the note I played. What the heck is going on!!??

 

[burns_isaac]

Sound post alignment problem? I checked inside the F-holes with a flashlight and I don't see anything moving around freely and the sound post is intact.

 

[Greg Clinkingbeard]

Check for an open seam.

 

[marvin spangles]

+1 on an open seam. It happened to me once. Took a while to discover it was an open seam in the lower bout.
Just hope is not a loose bass bar.

 

[burns_isaac]

It is a 10 year old Karl Reiser ply so....., but I didn't see anything that looked unusual as I was just looking around again. Bowed, the bass speaks fine with no "knocking" and even a normal pizz it's fine. The knock starts happening when I start digging in. Looks like I'll be seeing the luthier this week. Thanks gentlemen.

 

[360guy]

You could stick a light in the bass at night and look to see if you notice any light along the seams. Of course, it helps to turn off all the other lights.

OR... Fill it with water and see if it leaks from any spots.

 

[basshack]

Or you could seal up the F holes with putty and sink it in the bath and look for bubbles?

 

[burns_isaac]

Ha! Just like an a/c coil when you just can't find the damn leak. Or I can just take it to Joel up in Denton and let him sort at all out. I've heard he's really good.

 

[burns_isaac]

I will try the light thing. I feel ridiculous for even asking now because even if I find the problem I still have to take it to the luthier.

 

[fdeck]

Could be the portion of the peg that goes inside your bass vibrating. That happened to me on my Kay. I diagnosed it by playing the bass without the peg. Then I shortened it by 2 inches with a hacksaw and the resonance went away. If I sell it to someone 7 feet tall, I will have to report the issue.