Improvements in listening instruments for acoustic testing purposes

摘要

362,582. Detecting sounds. SCHAAFHAUSEN, W., 9, Gr. Allee, Hamburg, Germany. Oct. 6, 1930, No. 29933. [Class 13.] A listening instrument such as a tube or rod for acoustically testing machines and apparatus is combined with an adjustable Helmholtz resonator so that the general noise of the machine can be eliminated and particular sounds detected. In the simple form, Fig. 1, sound is conveyed by the tube or rod to a chamber a and diaphragm b, and passes through a hole d to the telescopic resonator c, e, the exit hole f being put to the ear. In Fig. 2, several concentric tubes or boxes 1, 5, 8 are assembled telescopically, and a sound box 14, with apertures which may be adjusted, is fitted at the base. An inner tube 10 can be pushed in to join the leading-in tube 15. A microphone, valve amplifier, and telephone receiver may be used to amplify weak vibrations before introducing them into the instrument.