More refined measurements of the complex reflection coefficients using single-frequency excitation and a lock-in amplifier for data analysis have revealed a limitation in the two-microphone transfer function technique for impedance tube measurements. A fixed choice of microphone positions for all frequencies as suggested by the current standard ASTM E1050-86 will compromise the accuracy of measurements. For accurate measurements, one of the microphone positions has to be close to a minimum pressure point of the standing-wave pattern, preferably the first minimum point. The choice of the other microphone position does not seem to be critical as long as the separation of the two positions is not close to a half-wavelength. The procedure employed in this study uses sequential sampling with one microphone instead of simultaneous sampling with two microphones. It presents a technique that is better than the existing standard methods for impedance tube measurements.