Wave
The propagation of vibration in acoustics.
What it means
A wave is the propagation of a vibration through a medium. With sound, this medium is as a rule the air: the movement of the vibrating body alternately produces compressions and rarefactions that propagate outward. The air itself does not travel along in the process — only the state is passed on, as with the rings on a water surface.
Musical use
Several quantities are practically significant. The speed of propagation in air is around 340 metres per second and depends on temperature; this explains why, in large spaces, the sound of a distantly seated part of an ensemble arrives noticeably later — a reason why, in wide formations, one must play by the conductor and not by ear.
Wavelength behaves inversely to frequency: low notes have long waves, high ones short ones. From this follows their different behaviour in a room. Long waves go around obstacles and penetrate walls, which is why the bass above all is heard from a neighbouring room; short waves are more strongly directed and more easily absorbed, which is why high notes sound clearer in a particular direction and are damped by an audience and curtains.
Added to this are reflection and superposition. Reflections off walls produce the reverberation; when waves are superposed, they can reinforce or cancel each other, which leads to uneven distribution in rooms. The beating of two nearly identical notes, too, is such a superposition.
Sound propagates in air as a longitudinal wave: the air particles oscillate back and forth in the direction of propagation and produce compressions and rarefactions. The speed at room temperature is about 343 metres per second. On strings, by contrast, transverse waves arise, whose superposition forms standing waves with fixed nodes.
Performance practice
Adjust to the room: in reverberant rooms, articulate more clearly and take things a little more calmly; in dry ones, bring more carrying power. In large formations, orient yourself by the beat, not by what you hear. And check the balance from the hall — at your own position it sounds different than for the audience.