With the advent of miniature high pressure microphones which can be used while a trumpet is being played, and the novel design of computer programs to interpret the data, we have, for the first time, been able to measure the outgoing and reflected sound waves for any note at a particular point in a trumpet.
The original aim was to investigate the mystery of the top octave from C6 (Bb trumpet pitch – 2 ledger lines above treble clef) up to ‘Super C’. However also looking at lower notes has revealed some interesting facts of particular interest to instrument designers and players.
The outgoing wave from the players vibrating lips travels at the speed of sound to the bell where some is reflected back to the lips, hopefully in synchronization, to create a note. Evidence suggests that ‘some‘ depends largely on the design of the trumpet and the skill of the player. We find that for lower notes, the reflection is high – approaching 100% – so most players including beginners are happy in this range. However, the higher notes of the top octave become more difficult to play since the reflection is reduced to about 10%. Only the most skilled players with the right instrument and mouthpiece can sustain a Super C, as demonstrated here by Derek Watkins!
What is also quite revealing in Figure 4 of our paper (see below) is that all players aiming for C6, for example, need to buzz the note for at least 10 milliseconds (or about 10 cycles) before a reflection from the bell reaches the lips to form a note – and only then if it is at the exact pitch. This means that the players must mentally hear the note and have the lips vibrating at the correct frequency before a sound is actually produced. So buzzing practice is good for you! Doesn’t this just reinforce what teachers and professors have been saying for centuries?
The following article appeared in the Journal of the Acoustical Society of America/ Volume 134/ Issue 2/ MUSIC AND MUSICAL INSTRUMENTS  and may be found at: http://asadl.org/jasa/resource/1/jasman/v134/i2/p1395_s1
Wave separation in the trumpet under playing conditions and comparison with time domain finite difference simulation
Jonathan A. Kemp, Stefan Bilbao, James McMaster, Richard A. Smith
Copyright 2013 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America.