I'm unqualified to speak about anything specific to horns, but I was once a metallurgist (PhD) with GE Aircraft Engines. Jet engines are carefully engineered not to "ring" for various reasons, especially that resonances can be VERY loud, and quickly lead to high cycle fatigue failure. But like horns, jet engines can make a beautiful sound (to an engineer). Unlike horns, the bell goes on the front.
Anyway, the frequency of resonances are related to just two material properties - density and modulus of elasticity (a measure of inherent stiffness). Those two properties are not particularly sensitive to alloying, and are not affected at all by deformation processing, microstructure or heat treatment. What I'm saying is that a chunk of brass will resonate at a frequency that depends only on the shape of the chunk. The alloy, how it was formed, whether annealed or not will not make much difference. (It will matter if you're making a chime that must ring at 440 Hz exactly, but I don't think we're talking about this sort of resonance for the bell of a horn. Perhaps some rather some sort of very diffuse resonance.) The stiffness of a bell will be greatly affected by wall thickness - different alloys and processes will produce different distributions of wall thickness within a bell. If two bells sound different, that's probably why. Annealing, cryo-treatments and that sort of thing will not affect the frequency of vibrations from a "thunk" or otherwise on a finished bell. Lacquer might, by adding weight and perhaps some stiffness. I can think of a possible exception: residual stresses could, I suppose, produce an affect similar to tightening the strings of a violin. "Annealing" is a bit of an all-purpose word - a heat treatment for this purpose would be called a "stress relief heat treatment". If I've written the above paragraphs carefully, I've only referred to the *frequency* of vibrations, not their amplitude. The only mechanical property metallurgists use that relates to amplitude is the "damping factor". This is a measure of the energy absorbed internally by a metal when it vibrates. It is the property that would tell you how long a chime would ring - in a vacuum, that is. Compared to other forms of damping, it may be a small factor. The energy that is emitted into the air as sound is likely to be much greater. Engineers who design turbine airfoils desperately want them not to ring too loud, but generally don't care much about a material's damping factor; the energy to be dissipated is much too great - they rely on other means. Is damping factor important for horns? I would not presume to know. It is certainly important for instruments for which the instrument itself makes the air vibrate - cymbals, say. And unlike modulus of elasticity, damping factor can be influenced by various "extrinsic" parameters, such as impurity levels, microstructure - annealing, perhaps. It depends on little features in the metal that can act like shock absorbers/dampers. Steels have notably high damping factors - impurity atoms can flop about in its relatively open crystal lattice. In brass - I don't know - face-centered-cubic crystal structures don't allow much of that. Sorry I don't have much specific knowledge about brass. I think it is safe to say that damping of a horn bell will be very strongly affected by contact with your hand. I can feel my bell vibrating if I hold it lightly. I can make greater contact with it if I want, and I sense that it does make a difference. I don't see much discussion about this factor. It wouldn't surprise me to learn that some people - perhaps without even knowing it - change their "grip" to produce different sounds. _______________________________________________ post: [email protected] unsubscribe or set options at https://pegasus.memphis.edu/cgi-bin/mailman/options/horn/archive%40jab.org
