Patent ID: 8917879

Claim:
An active muffler comprising: at least one microphone positioned in a space between a floor of an upper room and a ceiling of a lower room to detect noise from the upper room and output a noise signal; a flat speaker having a flat diaphragm spaced from the microphone; drive sections each supporting the flat diaphragm of the flat speaker to drive the flat diaphragm with n pieces of voice coils, n being a natural number equal to or more than 2, each of the drive sections including a respective support member supporting the drive section from the floor of the upper room, with the flat diaphragm located in the space; an opposite-phase signal generating section adapted to input the noise signal outputted from the microphone and generate a signal having a phase opposite that of the noise signal; n pieces of distance sensors respectively arranged near the n pieces of voice coils and each adapted to detect the distance from itself to the diaphragm and output a signal; n sets of feedback control sections adapted to input the opposite-phase signal generated by the opposite-phase signal generating section and the signals respectively outputted from the n pieces of distance sensors, perform feedback control so that the value of the signal outputted from each of the n pieces of distance sensors becomes closer to the value of the opposite-phase signal, and drive the n pieces of voice coils, wherein each of the drive sections is configured to sandwich the flat diaphragm of the speaker by a set of two voice coils of the n pieces of voice coils, and a same signal is inputted to each of the two voice coils of the set of two voice coils reversely to drive the flat diaphragm by a push-pull operation, and each of the drive sections includes a frame supporting a corresponding set of two voice coils of the n pieces of voice coils, and the support member for supporting the drive section is provided to the frame.