Abstract: Improvements are described for apparatus used in the measurement of acoustic admittance in ear canals including circuit means for permitting the measurement of relatively small acoustic volumes with an accuracy of better than one percent.

Abstract: An improved circuit for a transducer or loud-speaker as used in the measurement of acoustic quantities such as in impedance audiometers for providing accurate linear read outs.

Abstract: An improved loudspeaker system is disclosed which includes a passive electrical network between the speaker input and the output of a speaker driver for reproducing bass frequencies. The loudspeaker uses a closed box system and obtains an extended low frequency response through the use of critical relationships in the passive electrical network including high order transfer functions.

Abstract: A dynamic equalizer circuit is disclosed for the driver system of an electro-mechanical transducer such as a loudspeaker. The circuit provides an improved or leveled audio output and includes a protective arrangement which protects the transducer against damage from being overdriven. The protective arrangement includes a sensor which produces a continuous protective control signal based upon operating characteristics of the transducer such as transducer motion or temperature or fatigue.

Abstract: An improved multicontact switch is disclosed which has a molded plastic body supporting a molded plastic rotor. Metallic contacts are resiliently mounted on the rotor in position to engage and bridge a second set of contacts provided in the form of a printed circuit formed on an inner surface of the switch cover. A versatile multicontact switch pattern is obtained by an appropriate layout of the printed circuit contacts in combination with a particular mounting arrangement of the contacts on the switch rotor.

Abstract: An improved tympanometric testing means is described for automatically testing the status of the middle ear. The testing unit provides a recording on a chart showing a change in the compliance of the middle ear during change of the air pressure in the external ear. The tympanometric test unit operates automatically as the clinician inserts the test probe into the patient's ear. The unit automatically determines that the probe is in an unblocked condition and that the test probe tone is at a proper intensity relative to the ear canal volume. When these conditions are met and the ear canal pressure at the probe reaches the predetermined test start pressure, the unit proceeds with the testing as the pressure in the ear canal moves between desired limits such as between the +200 and -200 mm H.sub.2 O and while the recorder makes a plot of the ear drum compliance.

Abstract: An improved planar audio transducer or loudspeaker is described. It has a plastic diaphragm with a current carrying coil on one surface formed of aluminum conductors. A magnetic field is provided at the conductors from rows of magnets spaced from each other and mounted on opposite sides of the membrane on a pair of outer iron support members. A predetermined positioning of the magnets and a predetermined magnet and diaphragm spacing is provided by magnet mounting grooves in the iron support members and by surrounding the magnets with non-metallic frame members sandwiched between the iron magnet support members and the membrane.