Abstract: A tone control circuit includes a capacitor-resistor circuit; a resistor-capacitor circuit which is connected to the capacitor-resistor circuit; and a variable resistor which is connected between the resistor-capacitor circuit and capacitor-resistor circuit or a connecting point of both circuits. The variable resistor controls tone easily at high and low frequencies without change of the loudness when voice is output.

Abstract: The tone control circuit includes a capacitor-resistor circuit; a resistor-capacitor circuit which is connected to the capacitor-resistor circuit; and a variable resistor which is connected between the resistor-capacitor circuit and capacitor-resistor circuit or a connecting point of both circuits. Therefore, it can control the tone easily at high and low frequencies without change of the loudness (sensuous volume) when the voice is output.

Abstract: An ear plug to be inserted into the external auditory canal, having a compressible sleeve member and a core member attached therein, the improvement in which plural projections or a single projection are formed intermittently or continuously on an exterior of the core member, and vent is formed through or along the projection to make the external auditory canal communicate with the external atmosphere when inserted into the external auditory canal. A communicating passage or vent to an effective degree for remarkably decreasing the pressure difference between the inside of the external auditory canal and the external atmosphere as well as preventing leakage of sound causing so-called howling.

Abstract: A barometric meter such as barometer or a barometric altimeter comprises a vacuum chamber having a movable portion which displaces in proportion to air pressure. An aperture plate for allowing a light beam to pass therethrough is mounted to the movable portion of the vacuum chamber, and a light source stationary relative to the vacuum chamber is provided for illuminating the aperture plate. A photoelectric position detector disposed on the other side of the light source relative to the aperture plate and stationary to the vacuum chamber is provided for receiving the light beam which passes through the aperture in the aperture plate and for supplying an output indicative of the positional change of the light beam impinging on the photo-electric position detector. The output of the detector may be digitally displayed on a display as either air pressure or altitude.