ABSTRACT
This chapter deals with the principal experimental techniques involving the use of a constant wave source. These methods generally depend upon standing waves being formed inside an acoustic cavity and they are therefore effective when the walls of the enclosure reflect sound efficiently. This situation is readily achieved when the fluid is a gas but for liquids the characteristic acoustic impedance is a significant fraction of that for a typical wall material and the reflection coefficient can be much lower. Consequently, the steady-state methods have been most successful with gases up to pressures of order 10 MPa or so.
