Abstract: In an arrangement to prevent the intrusion of foreign matter into a transducer which extends with a projection provided with an opening into a sound channel of a hearing aid, a reduced need for space as well as simpler construction, compared with the state of the art, are achieved by means of the following characterizing features: A membrane made of pore-free material is provided, which has at least one bore for the passage of sound of from a few hundredths to a few tenths of a millimeter diameter, and in which the wall thickness of the membrane is small with respect to the diameter of the bore.

Abstract: A hearing aid has a housing which includes electronic components such as a microphone, amplifier, power source and receiver, as well as suitable structure for mounting and retaining those components. The housing is inserted in a cavity in a shell. The exterior of the shell is matched to the shape of the auditory canal of the user. The cavity of the shell in which the housing is received tapers to a smallest diameter at a sound discharge end of the shell. The housing also has a smallest diameter at this location. A releasable latch is disposed in the region of the smallest diameter for holding said housing in place within the shell during use, but permitting removal of the housing for repair or replacement without damaging the shell.

Abstract: The thread retainer has a tube which is slotted from the side to form an access opening for a thread and a gate member in the form of a ball which is movably mounted in the tube. The ball cooperates with a second ball to define a thread passage with curvilinear walls. The movable ball may move under gravity or may be spring biased to permit entry of the thread into the thread passage.

Abstract: A controlled layer of base mass is uniformly applied to a dental crown or bridge 10 of noble metal alloy by electrophoretic separation in a glass container 14 after an intermediate layer of galvanized zinc or tin is first applied in a container 13. The intermediate layer may be omitted if the crown or bridge is made of a non-noble metal alloy. The containers are provided with semi-cylindrical cathodes 15, 16 coupled to an electrical supply by jack plugs 19, 20. The crown or bridge serves as the anode and is held by tongs 21, 22 connected by cables 23, 24 to the power supply, and both the magnitudes and durations of the bath currents are adjustable. The liquid suspension of the base mass in the electrophoretic bath is maintained by a magnetic stirrer 27.