Posted by Klaus on September 30, 2001 at 19:19:37:
Please forgive me, that I take a thread to the top of the board under a new name:
When sousaphone bells add a ringing to the sound, and when they have an afterglow sounding after a note is stopped, then it is a matter of some of the player's energy being misconducted by the instrument into undesirable sonics.
As an owner/player of 3 bell front instruments I have had this problem close to me. But in a much lesser extend than should be expected.
My post-WWII German made York Master BBb has a 22" bell after a .750" bore. Absolutely no ringing.
My 1927 Conn 40K BBb sousa has a sub-standard 24" bell after a .734" bore. Absolutely no ringing.
My 1928 Conn 26 Eb Sousa (just 411## after the 40K in serial ##) has a 24" bell after a .695" (sic!) bore. I do not find myself bothered by any ringing to its sound, but I am no particular fan of its very remarkable afterglow. One might say, that I have been pre-inspired by Joe'S styrofoam block advise from the thread below. Only my version is, that I put my forehead on the backside of the bell rim.
The inspiration of this posting was Joe'S reporting of the (re-)introduction of a ringing to the sound, when he straightened the bell creases of the small Olds BBb sousa.
It made me wonder, in my non-metallurgist, but pretty-well-schooled-in-classical-mechanics way of thinking, about the possibility, that oversized, that is in relation to pitch, thoat, and bore, bells take up an uncontrolled acoustical existence of their own.
The two BBb's cited above have a large throat to rim (diameter) ratio. Allowing the airstream to control the acoustical happenings right out to the bell rim.
The 26K has a relatively less prominent throat diameter, as have also a number of smaller bored BBb sousas. A category, the Olds migh very well belong to.
My idea or theory cum guess is, that if the bell diameter exceeds some ratio in relation to the bore/bell-throat-diameter, then the outer areas of the bell take on a life of their own. They are provided kinetic energy from the airstream of the player. But the bore progression does not allow this airstream with its acoustical parameters to control the outer bell area, only to set that area into motion. A motion which is solely determined by the inherent frequencies of the metal of that area.
When the creased incarnation of the Olds baby sousa of Joe'S friend had no ringing as opposed to the straightened out end result, then I might go to the automobile production for an explanation.
When we look at the body of an automobile, we might experience the stamped forms of the steel sheets as an expression of the whims of a designer. Truly so.
But designers are not allowed whimming around solely to the outlines of their more or less creative minds. They have to provide stiffness to the automobile body. Be it for security, or be it for simple self-bearing properties.
Very few tuba/sousa bell creases are claimed to be designed at will. Yet they provide stiffness. And that potentially even to a degree, that it cancels out the inherent acoustical properties of a stampeding outer bell area.
Been long already I will leave a few more aspect to further discussions. If they are taken.