Acoustic theory
Classical acoustic theory derives from fluid mechanics, and centers on the mathematical description of sound waves. See acoustics for the engineering approach.In approaching the description of a sound wave the mathematics never give the whole story. The subtleties of thermodynamics are difficult enough to recommend a gradual familiarization with some related problems of vibration such as arise in mechanical sound production: motion of a spring, vibration of a string, equation of motion, harmonic.
Besides the math tools, the preceding examples help inform the beginner's physical intuition with analogies to the periodic compression domains.
The propagation of sound waves in air can be modeled by an equation of motion and an equation of continuity. With some simplifications, they can be given as follows:
is the acoustic pressure and 
is the acoustic fluid velocity vector, 
is the vector of spatial coordinates 
, 
is the time, 
is the static density of air and 
is the speed of sound in air.
Related articles
transfer function, sound pressure, acoustic impedance, acoustic resistance, law of gases, frequency, Fourier analysis,
instrumental acoustics, music theory voice production, formant, speech synthesis
