The Physics of Brass
Musical Instruments
4:00 p.m. (coffee @ 3:30)
It
is easy to think of a trumpet as a device for transmitting sound into a room.
Actually, very little of the sound in a trumpet escapes to the outside. Most of
the sound in a trumpet stays inside, where it forms standing waves that draw
energy from the player's lips. I will show why sound traveling in a tube tends
to reflect from an open end. Brass musical instruments consist of a mouthpiece,
a conical lead pipe, a cylindrical section, and a flared bell. I build a
trumpet to show the acoustical significance of these parts. Brass instruments
rely on valves (or, in the case of the trombone, a slide) to extend the length of
the tubing. In this they are unlike the woodwinds, which rely on side holes.
In the era before valves, horn players learned to augment their meager supply
of open notes by partially or completely blocking the air column with their
right hands. Even through the modern horn relies on valves (rather than on this
hand technique), horn players still keep their hands in the bell. I demonstrate
the acoustical and musical significance of the right hand in horn playing.