Modified two-microphone method: Determination of acoustic properties in upper audible and lower ultrasonic range using impedance tube based on two MEMS microphones

•Applied the two-microphone method in an impedance tube based on two MEMS microphones. This simple setup maintains the low-cost nature of the MEMS microphone application.•Extended the upper-frequency range of impedance tube application to fully cover the upper audible range and the lower ultrasonic range. The high-frequency range is getting increasingly more attention in the industry.•Applied adaptive sine excitation and curve-fitting technique to handle the strongly nonlinear frequency response of the measurement system. The presence of nonlinear frequency response is common in the application of MEMS microphones and the high-frequency range.•Overcome the intrinsic drawback of the two-microphone method caused by the coincidence of microphone positions with pressure nodes. The standardized two-microphone method is widely established for determining normal-incidence acoustic properties. Instead of numerous low-frequency usages, only a few high-frequency applications are reported. This paper provides insights into implementing the two-microphone method in an impedance tube based on two MEMS microphones for a frequency range of 5 kHz to 50 kHz. In doing so, we encountered technical issues associated with the MEMS microphone utilization and the high-frequency application. These issues can be addressed by implementing a modified method, in which an adaptive stepped sine excitation and a curve-fitting technique were applied. The modified method was validated by using three classical tube terminations, e.g., closed, open, and horn. The measured data of these terminations are in line with their analytic solutions. In conclusion, when proper concerns are taken, the acoustic properties up to the lower ultrasonic range can be determined using the modified two-microphone method in an impedance tube based on two MEMS microphones.