Investigation of headphones suitable for psychophysical experiments

In order to find the appropriate headphone to use in psychophysical experiments, the frequency responses of 12 headphones were measured by three physical methods: on an IEC coupler (B&K 4134), on a C coupler attached to a head and torso simulator (Kohken SAMRAI) (Okabe et al., J. Acoust. Soc. Jpn. (E) 5, 95–104), and by using a probe microphone in real ears. The results showed that very few electrostatic circumaural headphones (e.g., STAX SR‐Lambda Pro.) have relatively flat frequency characteristics, with excellent invariance among the measuring methods. In contrast, many dynamic supraaural headphones (e.g., Rion AD02, Beyer DT48, Elega DR831, etc.) have poor frequency characteristics, especially at lower frequencies, with many differences occurring between the three measuring methods. For these headphones, the energy leakage at the lower frequency region is inevitable, since the headphone pad fitting to the pinna is usually incomplete, and acoustic impedance of the diaphragm is very high. These undesirable characteristics might affect the results obtained in psychophysical experiments. As an example, results were severely affected by headphone differences in the vowel identification test using several synthesized vowels where the F0 component amplitude was manipulated. The physically determined frequency responses were compared with those from a psychophysical loudness matching procedure [K. Ueda and T. Hirahara, J. Acoust. Soc. Am. Suppl. 1 87, S142 (1990)].