Abstract: The active HVAC duct element can be inserted into a HVAC duct for attenuation of noise. The element works with an acoustical series arrangement of a passive acoustical component and an active acoustical component.

Abstract: The sound absorber is a combination of an acoustical transformer with an actively simulated acoustical impedance. The acoustical transformer transforms the high active impedance into a low impedance at the mouth of the transformer. The absorber is tuned by changing the active impedance.

Abstract: The actuator consists typically of two thin strips of material. One strip is made of e.g. steel. One surface of this strip is structured with tooth-like projections. To the tips of these teeth a second strip is attached. The second strip consists of e.g. piezoelectric material and is equipped with electrodes. Upon application of voltage the second strip changes its length and bends via the attached teeth the whole structure. The teeth-like structures provide stronger bending torque. The structure can also be used as a micromachined motor.

Abstract: The active HVAC duct element can be inserted into a HVAC duct for attenuation of noise. The element works with an acoustical series arrangement of a passive acoustical component and an active acoustical component.

Abstract: The loudspeaker system uses an inner transducer for pressure control in the closed loudspeaker housing to simulate the desired baffle properties. The speed of the membrane of the inner transducer is either proportional to the derivative of the pressure, or proportional to the intergral of pressure changes, or comprises summands proportional to the pressure, to the pressure's derivative and to the pressure's intergral.

Abstract: A thin, flexible foil acts as the membrane of the transducer. It is circumferentially connected to a rigid support structure which connects the foil mechanically with the transducer's driving coil. The foil is equipped with strain sensors which indicate the pressure upon the foil.

Abstract: The device simulates actively an acoustical impedance. The simulation is achieved by sensing the air pressure on the surface of the membrane of an electrodynamic transducer and by moving the membrane with a speed and an acceleration which depend upon the pressure according to the desired impedance function. It can be used in loudspeaker systems with closed housings to eliminate standing waves inside housings.