A hearing aid includes a microphone unit arranged in a hearing aid housing. The microphone unit is oriented in the housing relative to a microphone inlet element to cause a pressure equalization that allows acoustic cancellation of vibrations in the microphone unit.

The present invention provides an electret sheet that exhibits excellent piezoelectricity even by light stress. The electret sheet of the invention is characterized by including a charged porous sheet, in which the electret sheet has a compressive elastic modulus of 80 to 300 MPa when compressively deformed at 25 C. and a 50% compression stress of 120 to 300 kPa at 25 C., and thus has the excellent piezoelectricity for light stress and exhibits the excellent piezoelectricity even by light stress (0.5 N or less) caused by a pulse wave or a breathing.

The present invention provides an electret sheet that exhibits excellent piezoelectricity even by light stress. The electret sheet of the invention is characterized by including a charged porous sheet, in which the electret sheet has a compressive elastic modulus of 80 to 300 MPa when compressively deformed at 25 C. and a 50% compression stress of 120 to 300 kPa at 25 C., and thus has the excellent piezoelectricity for light stress and exhibits the excellent piezoelectricity even by light stress (0.5 N or less) caused by a pulse wave or a breathing.

A microphone having a housing including a bottom part and an upper part, and a transducer element which is arranged in the housing and is electrically and mechanically connected to the bottom part. For stress-free mounting of the transducer element, a flexible connecting element is proposed, which is pliable and/or compressible, is arranged between the transducer element and the upper part, and connects the transducer element to the upper part. The connecting element comprises a plastic, in which gas bubbles are distributed, the gas bubbles having a volume fraction of between 50 and 98% in the connecting element.

Magnetic field cancelling audio speakers and associated devices are disclosed. In one embodiment, a utility locator includes an audio speaker device with two loudspeaker drivers positioned and electrically connected to reduce emitted magnetic fields over a range of frequencies corresponding with locator sensing frequencies.

An electret element includes: an electret film that contains silicon oxide; and a protective film formed over the electret film and constituted of aluminum oxide deposited through an atomic layer deposition method.

A microphone circuit including a JFET or MOSFET transistor, one input of an impedance network connected to the transistor's gate, a terminal of a source resistor connected to the transistor's source, another terminal of the source resistor connected to ground, a bypass capacitor connected in parallel to the source resistor, one terminal of a load resistor connected to the transistor's drain, VCC_LOW connected to another terminal of the load resistor, an input of an op-amplifier connected to the transistor's source through a bi-directional low-pass-filter, another input of the op-amplifier connected to reference voltage, an output of the op-amplifier connected to another terminal of the input impedance network through an LPF, an energy detector connected to the transistor's drain via a coupling capacitor, an LPF connected to the energy detector output, and an LPF connected to the output of the energy detector, the input impedance network connected to a microphone.

A microphone circuit including a JFET or MOSFET transistor, one input of an impedance network connected to the transistor's gate, a terminal of a source resistor connected to the transistor's source, another terminal of the source resistor connected to ground, a bypass capacitor connected in parallel to the source resistor, one terminal of a load resistor connected to the transistor's drain, VCC_LOW connected to another terminal of the load resistor, an input of an op-amplifier connected to the transistor's source through a bi-directional low-pass-filter, another input of the op-amplifier connected to reference voltage, an output of the op-amplifier connected to another terminal of the input impedance network through an LPF, an energy detector connected to the transistor's drain via a coupling capacitor, an LPF connected to the energy detector output, and an LPF connected to the output of the energy detector, the input impedance network connected to a microphone.

A drive circuit is provided, which is used for driving an electrostatic film actuator. The drive circuit includes an input end, an isolation capacitor and a diode. The input end is used for receiving an input signal. The isolation capacitor includes a first end and a second end. The first end is electrically connected to the input end, and the second end is electrically connected to the electrostatic film actuator. The diode is connected between a working voltage end and the second end in a forward-bias direction, and an output signal is generated at the second end to drive the electrostatic film actuator.

A microphone includes a first micro electro mechanical system (MEMS) motor, the first MEMS motor including a first diaphragm and a first back plate; and a second MEMS motor including a second diaphragm and a second back plate. The first diaphragm is electrically biased relative to the first back plate according to a first voltage, the second diaphragm is biased relative to the second back plate according to a second voltage, and a magnitude of the first voltage is different from a magnitude of the second voltage.