Cooper W A, Parker D J
Ear Hear. 1981 Nov-Dec;2(6):283-93. doi: 10.1097/00003446-198111000-00008.
Standard audiometric transducers, such as the TDH-49, produce an electrical artefact which interferes with the recording of the early auditory evoked potentials. The sources of these artefacts have been identified as the capacitive and inductive coupling of the transducer and its leads to the recording electrodes. Artefacts were recorded using an artificial head with an M2-Cz electrode array for 500- and 3-kHz tone pips and positive, negative, and alternating polarity clicks at Peak Equivalent Sound Pressure Levels from 60 dB (positive click and 3-kHz tone pip) to 90 dB (alternating polarity click). The artefacts grew linearly with increases in intensity. Shifts in the Visual Detection Threshold of the artefacts produced by various conditions of shielding the transducer and its leads were explored. Acceptable reductions in artefact magnitude were obtained by enclosing the transducer in either an aluminium or mu-metal case connected through a braided-wire shield of the transducer leads to earth ground. Lesser reductions were achieved by the use of antiphase cancellation. The combination of the latter and the aluminum and mu-metal cases did not produce greater shifts in the visual detection threshold than the use of the aluminum and mu-metal cases alone. The fabrication of a pair of shielded enclosures is described and data are presented which show that they do not adversely affect the acoustic output of the headphones.
标准听力换能器，如TDH - 49，会产生电伪迹，干扰早期听觉诱发电位的记录。这些伪迹的来源已被确定为换能器及其导线与记录电极之间的电容性和电感性耦合。使用带有M2 - Cz电极阵列的人工头记录伪迹，针对500赫兹和3千赫兹的纯音短声以及峰值等效声压级从60分贝（正性短声和3千赫兹纯音短声）到90分贝（交替极性短声）的正性、负性和交替极性短声。伪迹随强度增加呈线性增长。研究了在各种屏蔽换能器及其导线的条件下产生的伪迹的视觉检测阈值的变化。通过将换能器封装在铝制或磁导率高的软铁金属盒中，并通过换能器导线的编织线屏蔽接地，可获得可接受的伪迹幅度降低。通过使用反相抵消实现的降低幅度较小。与单独使用铝制和磁导率高的软铁金属盒相比，后者与铝制和磁导率高的软铁金属盒的组合在视觉检测阈值上并未产生更大的变化。描述了一对屏蔽外壳的制作过程，并给出了数据，表明它们不会对耳机的声学输出产生不利影响。
