Individual Frequency Components Research Articles

Transformer Noise Measurement Methods [includes discussion

The present sound level index of transformer noise is discussed and compared with two of several other indexes considered by the Committee. These are loudness level and audibility. It is believed that the index of loudness level is more indicative of disturbance from transformer noise than is sound level. However, measurement of loudness level is more complex since it requires some form of frequency analysis and more or less extensive calculation. Furthermore, loudness level does not decrease following the law of spherical divergence even though the attenuation of the individual frequencies may follow this law. Therefore the loudness level has to be calculated for each distance of interest. The audibility index depends on the intensity of the individual frequency components above ambient noise. Data are presented which indicate when the intensity of the individual components will be great enough to make them audible. Determination of audibility is most precise when based on measurements involving frequency analysis. However, the limited data now available point to the possibility of using only the sound level meter with its A weighting network for this method. Measurements made with the sound level meter can be used to determine the distance betwen transformer and residence necessary for just achieving inaudibility. However, it is not to be inferred that inaudibility is necessary for satisfactory installation. Experience curves are presented which indicate that the level may be raised above inaudibility without giving rise to significant reaction.

THE RESPONSE OF SINGLE AUDITORY-NERVE FIBERS TO ACOUSTIC STIMULATION

THE AIM OF the experiments described here was to study the response of single auditory-nerve fibers to acoustic stimulation delivered to the intact ear. Similar studies on other single afferent fibers have remarkably extended knowledge of the mode of action of diverse sensory mechanisms, while at the same time emphasizing their fundamental similarities. The present report describes the behavior of single auditory fibers and stresses similarities to other sensory nerves; in a subsequent paper we hope to relate these findings to a specific theory of action of the mammalian cochlea. METHOD Young cats anesthetized with dial (0.75 cc. per kilo) were used in these experiments. The postero-dorsal aspect of the auditory nerve was exposed by removing the lateral portion of the occipital bone where it meets the petrous bone. Bleeding from the sinus petrosus inferior was stopped by judicious cauterization or by Clotting Globulin. * A Ringer-filled glass micropipette with Ag-AgCl wire inserted as close as possible to the tip served as the active lead from the nerve. It was early established that pipettes with openings greater than 5~ do not allow isolation of the action potentials of single auditory fibers. The 3 to 5~ electrodes used have an impedance of about 1 megohm when tested on a resistance-capacity bridge between 0.6 and 2.5 kc. The microelectrode and the indifferent electrode (a silver plate in the neck muscles) led to a capacity-coupled amplifier (Grass) with an input done photographically