Cal Poly Pomona

Physics Seminar

Friday, May 2, 2008

The Physics of Brass Musical Instruments or What do horn players do with their right hands, anyway?

Brian Holmes

Physics, San Jose State University

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 leadpipe, 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.

Demonstrations are used to answer the following questions:

  • What determines the frequencies of standing waves on a spring?
  • Why does changing the end of a spring from a node to an anti-node lower the frequency of standing waves on the spring?
  • Why does most of the sound in a tube reflect from an open end, rather than being transmitted into the room?
  • How to build a trumpet: how do the bell, mouthpiece, and leadpipe contribute to the acoustics of a brass instrument?
  • Why must trumpets use valves instead of holes in the side?
  • Why can a bugle (unlike a trumpet) use side holes?
  • Why does blocking the air column in the bell of a horn with the right hand lower the frequency of standing waves in the horn?
  • •  How has this right hand technique influenced the historical and musical development of the horn?
  • Why does the hand remain in the bell of the modern horn?

Refreshments at 4:00 PM. Seminar begins at 4:10 PM.
Building 8, Room 241
For further information, please call (909) 869-4014

Last modified on April 19, 2008
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