Acoustical properties of the B♭ trumpet were investigated. By comparing two trumpets judged to have good and poor musical quality, respectively, it was found that the air leakage at the pistons reduced theQvalue of the resonance. An irregular frequency distribution of the higher normal modes of the trumpet was also studied. The effect of the connecting condition of the tube and horn of the trumpet on the harmonic relation of the normal modes of the air column was studied. The measured resonance frequencies were found to agree well with the maximum driving point radiation resistance computed for various combinations of tube and horn.