A Proposed Quality Criterion for Tubes Used for Measuring Acoustic Absorption and Impedance

The elementary transmission line theory cannot be applied to the measurement of acoustic absorption and impedance using the stationary wave-tube method when there are appreciable energy losses in the sound wave arising from the presence of the tube walls, and it becomes necessary to invoke more complicated procedures.

By means of the wave theory, the errors between the measured and the correct values of the acoustic absorption and impedances, due to measuring tube losses, are analysed.

Abacuses are provided to calculate the recorded experimental errors, as a function of directly measurable quantities, R, λ ₀ and d ₀ (distance from rigid end to first minimum).

Finally, and as a corollary, a quality criterion is proposed for the classification of tubes to be used for measurements of acoustical absorption and impedance.