Re: Re: Metallurgy

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

Posted by Rick Denney on January 31, 2001 at 17:28:51:

In Reply to: Re: Metallurgy posted by Rick Denney on January 30, 2001 at 18:40:37:

A general response to BassBone, Jim, and Henry:

I'm not sure that the experiences recorded for trombones or horns translate to tuba. Those instruments have a significant component of brassy edge in their characteristic sound, with the sibilance of the metal contributing important overtones. This is much less the case for tubas. This might be less the case when the horn is overblown.

Even so, Dr. Young, as I recall, mentioned testing that he did on trumpets, with no measurable difference when other factors were controlled. While I don't agree with his objectives, I have complete respect for his science, and his results bear strongly on this issue. If I'm remembering his results incorrectly, I hope he will enter this thread and correct me.

It's not easy to compare horns based on the material, when there are many other potential differences. It would seem to me that subtle differences in material thickness and geometry, while obvious on visual inspection, might be making the difference you hear.

I'm guessing here; I don't actually know. I just can't think of how the dynamic responses of the metal, and stresses below yield strength, will be significantly different with small differences in alloy.

Does anyone have handy the modulus of elasticity of different alloys of brass?

And on the subject of damping (which enters this conversation from another angle), nearly all metals--and certainly all brasses--are highly elastic. That means not that they are flexible (which is the common misunderstood meaning), but that they give up energy as efficiently as they store it. A rubber band is not very elastic though is is highly flexible. Stretch it and it returns to its former shape fairly slowly. Do it a bunch of times and it gets warm. This is the friction within the material. Metals don't have that friction, and you can compress and release a spring a zillion times and it won't get hot. If it doesn't get hot, then it's not storing energy, and if it's not storing energy, then it isn't damping the sound production. Softer metals such as copper don't damp vibration any more than hard metals such as brass. But copper, being more malleable, may have some other property resulting from manufacturer, such as lower residual stress, that I'm unaware of.

Rick "trying not to draw too many conclusions" Denney

Follow Ups: