The basic differences between thermoacoustic theory and traditional theory are reviewed. The first is a difference of image. Traditional theory discusses only enthalpy flow, while thermodynamic theory discusses not only enthalpy flow but also entropy flow and work flow in conjunction with the second law of thermodynamics. Definitions of these flows in the traditional theory are vague and sometimes conflict with both the first and second laws of thermodynamics, while the definitions in thermoacoustic theory are clear and consistent to thermodynamics. The concept of a state variable plays a key part of thermodynamic discussion regarding thermoacoustical phenomena. The last difference is related to transverse averages. Most people who follow traditional theory discuss the transverse averages of oscillating quantities at first, and after that, handle the product of oscillating quantities. Thermoacoustic theory discusses transverse distribution of the oscillating quantities at first and then handles the transverse averages of products of oscillating quantities. Since the product of averages and the average of a product are different in general, results of those following traditional theory are different from those obtained by thermoacoustic theory. This is one of the reasons why thermoacoustic theory succeeds in discussing a wide variety of thermoacoustic phenomena including intrinsically irreversible phenomena.
