The effect of a slow steady flow of ideal fluid upon a superimposed pure‐tone sound field is examined, especially for effects upon the acoustic admittance vector. It is assumed that the total field is derivable from a scalar potential and that terms of second order in Mach number are negligible. Blokhintsev's transformation [NACA Tech. Mem. No. 1399(1956)] to a flowfree acoustic problem is shown to be awkward, except for rigid, nonporous boundaries, because of complications in the transformed boundary conditions. For one dimensional fields, it is shown that the steady flow has no direct effect on the acoustic admittance or the magnitudes of acoustic pressure and particle velocity. However the steady flow may affect the terminating admittance of a one dimensional field, and thereby become evident within that field. If the correct value of terminating admittance is used in the analysis, then a flowfree acoustic solution will yield correct values for the magnitudes of the true pressure and particle velocity and for both magnitude and phase of the true admittance at every point.