Posted by Sven Bring on June 17, 2001 at 05:35:04:
A couple of days ago, I asked for some kind of explanation for the benefits of heavy valve caps. Since nobody answered, I'll venture my own amateurish thoughts in the hope of getting a more knowledgeable reaction.
Apart from the resonances of the air column, which are dependent mostly on tubing length and taper, a brass instrument will also have resonances in its metal body, depending on its mass and its distribution. These are probably generally without any "meaningful" relation to the tone frequencies produced. Since they surely interact in some way with the vibration of the air column, they might be a disturbing element.
Now, making parts of the valve system heavier will lower the resonances of the mechanical system. However, the mass of the mechanical system is fixed, and so, I think, will its resonances be. The vibrations of the metal will travel mostly through the metal, and so won't be changed much by opening valves. If so, it will strengthen the same resonance frequencies of the air column all the time. I cannot see why placing these resonances at lower frequencies should make the instrument project better.
Another possibility is that lowering the mechanical resonance would place it at frequencies too low to interfere with the tones produced, which might be beneficial.
I'd welcome other's thoughts about this.