Re: Re: Re: Vibration, damping, and weight


[ Follow Ups ] [ Post Followup ] [ TubeNet BBS ] [ FAQ ]

Posted by John Swensen on August 17, 2001 at 16:34:14:

In Reply to: Re: Re: Vibration, damping, and weight posted by Rick Denney on August 17, 2001 at 14:58:39:

On stiffness, I agree with you, but there is also damping of vibrations.
A lead bell (the kind with a clapper, that you shake), will just thud at room temperature but, when cooled with liquid nitrogen, it rings like a proverbial bell.

Similarly, high carbon steel, in the annealed state, will ring for a while, but will ring much longer when hardened (some machinists can tell if a piece of steel is hardened by tapping it with a hammer and listening for the resulting sound).

If there really is a difference between the sound of a work-hardened (work-strengthened, if you like, but isn't hardness directly related to yield strength?) tuba bell and one that is, more or less, annealed, assuming no shape changes during annealing) then that difference must be due to the damping of the bell's vibrations. Maybe it is a matter of bell vibrations interacting with air column vibrations, as Schilke suggested, maybe it is due to energy being dissipated within the metal at different rates.

I am unaware of an experiment that might indicate if annealing a bell makes a difference in playing, but it sounds like something Schilke might have done. One such experiment might take two close-to-identical bells (say trumpet bells, for cheapness) put them on one or more trumpet bodies and evaluated, then one bell is annealed, and the same group blindly evaluates the same pair of bells (that is, without knowing which bell was annealed; it could be dark and the players could wear gloves). After this, both bells would be filled with molten lead (which melts below the annealing temperature for brass), the brass etched away in acid, and the two lead cores carefully measured for any shape changes during annealing. Repeat the process until two identical lead cores come out, or the experimenters conclude that annealing always changes the bell shape (or they run out of bells).


Follow Ups: