In order to isolate some of the factors affecting the internal tuning of brass instruments several differently tapered bells were made and a trumpet made up such that the different bells could be easily attached and detached. Tests were then run on the internal tuning using both a physical measure of the trumpet air column resonant frequency and a group of five players. The results were analyzed statistically and indicate that changes in the shape of the bell taper as great as those used for these tests caused significant changes in internal tuning, and that these changes were functionally related to the type of taper. Secondary results of the analysis gave measures of the magnitude of the differences among players and trials and showed the relationship between the player average and the physical measure of air column resonance.