Abstract: An acoustic filter (100) comprises a filter housing (10) with an acoustic channel (11) and acoustic valve (20) in the channel. The acoustic valve (20) can be moved to along a trajectory (S) between positions (P1, P2). An actuator (30) is configured to actuate the acoustic valve (20) along the trajectory (S). The actuator (30) comprises one or more mechanical elements (31,32). The mechanical elements can move the acoustic valve (20) along at least an initial part of the trajectory. The actuator (30) comprises one or more magnetic elements (41, 42) with a magnetic field (M1,M2) configured to exert a magnetic force (Fm) on the acoustic valve (20). This may help to move the acoustic valve (20) to the second position (P2) along a final part of the trajectory and keep the acoustic valve (20) at the second position (P2). Accordingly the stroke of the valve can be enhanced.

Abstract: An acoustic filter including a valve system with acoustic valves arranged in a sound passage for controlling the acoustic resistance of respective apertures based on a control signal for selecting an attenuation of a sound pressure level of transmitted sound compared to that of received sound. The acoustic filter is adapted to provide the selection of the attenuation from a sequence of predetermined attenuations based on a selection of the control signal. Each attenuation in the sequence corresponds to acoustic valves providing the apertures with a respective predetermined acoustic resistance, wherein the acoustic resistances of subsequent attenuations in the sequence are adapted to correspond with a linear increase or decrease in the attenuation of the sound in decibels.

Abstract: An acoustic filter (100) comprises a filter housing (10) with an acoustic channel (11) and acoustic valve (20) in the channel The acoustic valve (20) can be moved to along a trajectory (S) between positions (P1, P2). An actuator (30) is configured to actuate the acoustic valve (20) along the trajectory (S). The actuator (30) comprises one or more mechanical elements (31,32). The mechanical elements can move the acoustic valve (20) along at least an initial part of the trajectory. The actuator (30) comprises one or more magnetic elements (41, 42) with a magnetic field (M1,M2) configured to exert a magnetic force (Fm) on the acoustic valve (20). This may help to move the acoustic valve (20) to the second position (P2) along a final part of the trajectory and keep the acoustic valve (20) at the second position (P2). Accordingly the stroke of the valve can be enhanced.

Abstract: An acoustic filter including a valve system with acoustic valves arranged in a sound passage for controlling the acoustic resistance of respective apertures based on a control signal for selecting an attenuation of a sound pressure level of transmitted sound compared to that of received sound. The acoustic filter is adapted to provide the selection of the attenuation from a sequence of predetermined attenuations based on a selection of the control signal. Each attenuation in the sequence corresponds to acoustic valves providing the apertures with a respective predetermined acoustic resistance, wherein the acoustic resistances of subsequent attenuations in the sequence are adapted to correspond with a linear increase or decrease in the attenuation of the sound in decibels.