Posted by Sven Bring on May 31, 2001 at 15:37:52:
In Reply to: Mouthpieces, pitch and display stands posted by Les Smith on May 31, 2001 at 12:30:12:
There's a lot of vodoo around mouthpieces, but there is also some systematic, experimentally based knowledge. In particular, the physicist Arthur Benade has written about this in his book "Fundamentals of Musical Acoustics". His main conclusion is that there are two mpc characteristics that are vitally important for intonation: total inner volume of the mpc and its "popping frequency" (the tone you hear if you slap the blowing end of the mpc against the palm of your hand).
The contribution of the mpc to the intonation characteristics of the instrument can be likened to an added piece of tubing. Mpc volume and popping frequency are the main characteristcs which determine the length of this "virtual" tubing. What makes it complicated is the fact that the virtual length of hte mpc varies with the frequency of the tone played.
If I haven't lost you already, this is an attempt to sum up his results:
An instrument which tends to play flatter with a crescendo can benefit from a mpc with a higher popping frequency. The virtual length of the mpc is too long for higher frequencies. This lowers the tuning when you play louder and more of the higher partials are engaged. To increase the popping frequency without decreasing the mpc volume, you make the bore (the narrowest part) bigger. An instrument that goes sharper in a crescendo is a harder case. It's difficult to decrease popping frequency without changing to a mpc with either bigger volume or narrower bore or both.
The following is a direct quote from his book: "Brass players have built up an enormous lore about the influence of mouthpiece cup depth and back-bore shape on the tone and response of their instruments. Much that is mysterious in their observations becomes clear when it is recognized that easy blowing, clear speech, and good tuning all are dominated by the the relationship of the total mouthpiece volume and the popping frequency. If these are not suited to the instrument, one musical effect must then be bought at the expense of another."
I'm not sure I've understood all of this, but I know I've got good results when following his recommendations.
Sven