Influence Of Replaying Earphones On Measurement Values Of Simultaneous Masking Threshold

In the paper, three earphones are calibrated on KEMAR manikin. At the meantime, we get the calibration curves. Then, Headphone to Eardrum Transfer Function (HETF) is measured. The repeatability of three HETF is analyzed. From these works, a conclusion is reached as follows: at high frequency and low frequency domain, the HETF repeatability of ER-2(an insert earphone) is better than that of DT770pro and HD250 (both are circumaural headphones). Therefore, ER-2 is more ease to be calibrated. Finally, experiments of measuring the thresholds of simultaneous masking are conducted for 4 subjects. According to experiment's results, we know that at high frequency range, ER-2 has the best repeatability.The paper is consisted of two parts. In the first part, the HETF of three earphones on KEMAR manikin are measured and its repeatability is analyzed. According to the results, in the frequency range between 50Hz to 18000Hz, the ER-2 has a most smooth HETF among three earphones and has the lowest sensitivity to the earphones'location. So its repeatability is the best one. The reason is that compared with insert earphone, circumaural headphones are not only affected by the characteristics of ear canal, but also the characteristics of pinna. Particularly, in the frequency around 9kHz, there is a clear valley in the HETF of the circumaural headphones. Such valley is very similar to the valley of HRTF (Head Related Transfer Function) in the nearby frequency range. It indicates that the pinna has a great influence on the HETF of circumaural headphones around 9kHz. In contrast, ER-2 is not affected by the pinna. So its HETF is much smoother and has a good repeatability.In the second part, the simultaneous masking thresholds on real person are measured by using three earphones as sound source respectively. Firstly,The tests are made in the intermediate frequency range, a pink noise with frequency between 920Hz to 1080Hz is used as masker, a 1000Hz pure tone is used as maskee. According to the results, we find that all earphones can get similar thresholds and have similar repeatability. Such phenomenon is consistent with the results obtained in the testing on KEMAR manikin. Then, tests in the high frequency range are made: pink noise with frequency between 7700Hz to 9500Hz is used as masker, a 9100Hz pure tone is used as maskee. According to the results, we find that all earphones have quite different thresholds. However, ER-2 has the best repeatability. Such phenomenon is also consistent with the results obtained in the testing on KEMAR manikin.According to the performance of three earphones in above experiments, ER-2 can be generally considered as having the best overall performance, especially in high frequency range. So ER-2 is more suitable to be used as sound replaying earphone in the experiment of simultaneous masking threshold measurement.