Double Bass Body Resonance (pre-feedback)

[BassDuex]

I have a '42 Kay, full circle, U5, iAmp800, Wizzy 12/10

I really don't have feedback problems, but there is a 'resonance' that hums through the body which muddies the tone.
It sound weird, and even stranger to type - but if I hold/squeeze the bass body between my knees as I play - it's Perfect!

Are there any ideas on how to physically dampen that - like maybe a 2nd soundpost or some sort of strap th tighten around the body?

 

[DoubleMIDI]

Maybe an open seam? Visit your luthier for help.

 

[Alib8]

I have a CCB with a similar problem, I was suspicious of the metal endpin rod resonating, so I stuck a t-shirt through the f-hole to sit at the base. I suggest tying a knot and leaving a bit of the fabric outside the f-hole so that you can pull it back. Seems to have worked.

 

[arnoldschnitzer]

If you have not done so already, wind a piece of foam or other soft material through the strings below the bridge. This will effectively shut off the sympathetic sounding of the string afterlengths, which your pickup does not realize it should ignore.

 

[BassDuex]

I did have it at a Luthier, he inspected everything and reported a clean bill of health.

Good point on the after length, and internal end pin post - I hav tried those yet - but I have tried lodging a racquet ball between the tailpiece and bass top.
The issue is demonstrated by simply 'knocking' on the top and listening to THAT resonace as it fades - that seems to be the sound that muddies things when amplified.

Thoughts?

 

[DoubleMIDI]

I would say either go back to that luthier and show him what you mean or visit a different luthier. Maybe your luthier didn't recognize this problem by himself, but if you show it to him, he might be able to help.

 

[james condino]

One of my basses gets a seasonal rattle right around the soundpost. A tiny little adjustment and it goes away.

 

[BassDuex]

Good to know.
I'm actually relocating near Santa Cruz and figured there has got to be some super great luthiers down there

 

[megafiddle]

"Feedback" normally refers to the audible howling that occurs when amp gain is high enough to cause sustained oscillation. But even if this audible feedback is not occuring, the feedback path still exists and can have a large effect on the frequency response of the whole setup. The natural resonance of the bass will cause a peak in the frequency response. The distance between bass and speaker can also have an effect on the frequency of the peak. This is especially true when the gain is set just below the level that causes sustained howling.

So what happens is that the feedback path from speaker to bass causes unusually high gain, higher than you might expect from the volume level. And the natural resonance and physical placement of bass and speaker determine the frequency band of this extra high gain. As long as the gain is set below the critical level which causes sustained oscillation, you won't hear the charactistic howling of feedback. But if the gain is set high enough, you will hear tones ringing out for unusually long periods, or boominess, depending on the feedback frequency.

You can test this easily by placing the speaker so that it projects out through a doorway into another roon, or even to the outdoors. Or listen through headphones with speaker off, if possible. If the problem is gone, then the problem is simply this "inaudible feedback", and not the bass.

One solution is to reorient or move the bass and/or speaker. Another solution is to use an EQ to lower the offending frequency band. An EQ is not as bad as it might sound, as the band was too high to begin with; it restores a more level response.

-

 

[MaxJohnson]

The things that make an acoustic instrument projective and detailed, are precisely the things that will get out of control when heavily amplified.