Canning D M
Royal National Institute for the Deaf, Audiometer Calibration Laboratory, Glasgow, UK.
Br J Audiol. 1991 Dec;25(6):429-31. doi: 10.3109/03005369109076621.
Since the adoption of the Telephonics TDH39 pattern of earphone as the main audiometric earphone in use in Britain and elsewhere, there have been a number of superficial changes in its design. The most significant change was around 1980 when the metal-cased design was replaced by a plastic-cased version: the TDH39P. At that time it was assumed that the new earphone was equivalent to the metal-cased version since both types of earphone exhibited similar frequency responses as measured on the IEC 303 acoustic coupler. However, it has been found, through measurements taken during the course of routine audiometer calibration, that the two types of earphone appear to exhibit a significant difference in the measured SPL at 6 kHz when they are compared using an IEC 318 wide-band artificial ear.
自从采用Telephonics TDH39型耳机作为英国及其他地区使用的主要听力计耳机以来，其设计有了一些表面上的变化。最显著的变化发生在1980年左右，当时金属外壳设计被塑料外壳版本TDH39P所取代。当时人们认为新耳机与金属外壳版本相当，因为在IEC 303声耦合器上测量时，两种耳机的频率响应相似。然而，通过在常规听力计校准过程中进行的测量发现，当使用IEC 318宽带人工耳进行比较时，这两种耳机在6 kHz处测得的声压级似乎存在显著差异。
