Abstract: A particle spacing and metering device having a supply hopper above a pair of contra-rotating rollers. An aperture in the floor of the hopper is provided with a regulator which controls the flow of particles to the rollers. The regulator has a body fixed to a shaft rotatably mounted in the aperture. A cam-type metering face has a groove of increasing depth and width to enable selected variation of a throat through which the particles flow.

Abstract: The disclosure relates particularly to audiometers, such as used in ascertaining the hearing ability of test subjects. Functionally, the new audiometer is similar to the so-called von Bekesy audiometer. However, the new system incorporates unique and advantageous circuit arrangements which enable controlled variable attenuation of a power signal to be achieved through simple and reliable electronic means. The new system eliminates the costly and fast-wearing electro-mechanical mechanism customarily used and heretofore considered necessary in a von Bekesy audiometer. The new electronic attenuation system includes means, effective in the extremely low power range of audiometer signal generation, to apply a high level, controllably variable signal, and to attenuate that signal across a high ratio voltage divider.