A new method to estimate sound energy entering the middle ear

Standing waves in the ear canal can cause inaccurate quantification of the sound pressure level (SPL) entering the ear and therefore lead to unreliable results in clinical tests. Since it is impractical to directly measure the SPL at the eardrum position, in this study we proposed a new method to estimate the eardrum SPL by solely making measurement at the entry of the ear canal. To achieve this, the acoustic characteristics of the earphone were calculated using a calculation tube with variable lengths. Then the ear canal impedance was calculated according to the obtained source characteristics. Finally, the eardrum SPL was estimated by the ear-canal impedance and the SPL measured at the entry of the ear canal. The results showed that the eardrum SPL could be reliably estimated for all the five subjects participated in this study. The maximal estimation error was less than 3 dB for all frequencies from 0.5 to 10 kHz. These findings suggested that the proposed method could avoid the standing wave problem and therefore might be a great candidate for accurate calibration of sound pressure in various acoustic measurements.