Comparitive Analysis of Direct and Indirect Measures of Attenuation and Speed of Sound

This research compares 2 estimation methods of parameters critical for acoustic simulation and microphone array applications. In particular, sound speed and attenuation were estimated directly with actual microphone and speaker arrangements and indirectly based measurement of temperature, humidity and air pressure. It is more practical to measure the speed of sound and attenuation indirectly because they only depend on factors that can be relatively easily obtained. Measuring the speed of sound directly involved recording a sound emitted by sources and microphones positioned collinearly. For the indirect method, we found the average values of the temperature, humidity and air pressure and calculated the speed of sound and attenuation using closed form expressions. Direct and indirect estimates from measurements in a laboratory environment were compared using a paired t-test. Results show that indirect measurement can be used in phase of direct measurements with no significant loss in accuracy. The simulator emulated the experimental results well. The speed of sound estimated indirectly was ±0.031% m/s away from the directly measured results. Additionally for real-time beam formers or sound source locators, if temperature, humidity, or pressure changes, they can be easily monitored and acoustic parameters can be adjusted accordingly. Thus showing that an approximation is viable substitute for the directly measured speed of sound and attenuation function.