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Thomas R. Moore
Postal:
Department of Physics Rollins College Winter Park, Florida 32789 USA
Email:
tmoore@rollins.edu
The Acoustics of
Brass Musical Instruments
All brasswind instruments have several things in common but being made of brass is not one of them.
The history of brass musical instruments is as long and varied as civilization itself. Although the recorded history of civilization predates the manufacture of brass by several millennia, it is not the material from which the instrument is made that classifies a musical instrument as being a member of the brass family. Rather, it is the fact that the sound originates from vibrations of the player’s lips. This sound from the lips, colloquially referred to by some as a raspberry or Bronx cheer, is the driving oscillation for all members of the brass family. During play, the lips open and close periodically and release a train of pulses of air into the instrument simi- lar to the action of the reed of a woodwind instrument, and, indeed, the oscillating lips are usually referred to as a lip reed by acousticians.
Technically, these instruments are called labrosones, and it is not clear when they began being referred to as brass instruments or, more correctly, brasswind instru- ments. To make things more confusing, not all wind instruments made of brass are brasswind instruments. Instruments in the brass family have been made from wood, shell, animal horn, ceramics, tree bark, various metals, plastic, and even human bones. But the saxophone, which is made entirely of brass, is not a brass instrument.
Considering the cultural and geographic diversity of the people who play brass- wind instruments, the long list of construction materials is not unexpected. In- deed, the only surprising material in the list may be human bones. It is well-known that animal bones were used in antiquity for flutelike instruments (Zhang et al., 2004; Atema, 2014), and they are still used today as percussion instruments in some cultures. But the use of a human bone for a musical instrument is unusual. In most cultures, human bone is not an acceptable material from which to make mu- sical instruments; however, there are documented cases of trumpets made from human bones in some Amazonian and Himalayan cultures (Baines, 1976). In an interesting note, Baines recounts that after the body of one of the first Europeans to be buried near Darjeeling was interred, it was promptly dug up by members of a local sect so they could use his “trumpet bones.” Evidently, the femur makes a serviceable trumpet and the unfortunate victim was a very tall man.
In addition to the wide variety of materials and shapes, brass instruments may have valves, slides, or holes that can be used to play different pitches, or it may have none of these. The large catalog of ancient and modern brass instruments makes it difficult to address the acoustics of the family in much detail. However, by initially limiting the discussion to the most familiar members of the brass family, it is possible to understand much of the underlying physics of all brass instruments. Therefore, for the purpose of investigating the acoustics of the family of brasswind instruments, it is useful to begin by considering a single instrument and then dis- cussing some of the important differences between this instrument and its siblings. To this end, consider the modern trumpet.
30 | Acoustics Today | Winter 2016 | volume 12, issue 4 ©2016 Acoustical Society of America. All rights reserved.