Section 14
Sound
The speed of sound is the product of wavelength and frequency.
For spherical propagation
Sound intensity is acoustic power per unit area.
con
The intensity level is ten times the common logarithm of the ratio I/I₀.
The perceived frequency depends on the velocities of the source and the observer relative to the medium.
Convention: the sign of the numerator is chosen according to the observer's motion toward/away from the source; that of the denominator according to the source's motion toward/away from the observer.
The beat frequency is the absolute value of the difference of the two frequencies.
Resonance frequencies of a tube open at both ends, integer multiples of v/(2L).
Resonance frequencies of a tube closed at one end, odd harmonics of v/(4L).