| 摘要 |
PURPOSE:To vary frequency characteristic by forming a hollow duct slidably at one side of a speaker box and moving it so as to vary the volume of the speaker box. CONSTITUTION:A cylinder 5 is provided opposite to a dynamic speaker unit 4 in the speaker box 5 and a duct 2 is fitted thereto. The cylinder 5 is able to be moved in forward/backward direction and the volume of the cavity 6 is varied and the resonance frequency is varied. A sounder 7 of an electronic musical instrument is operated, the signal is converted into an electric signal by a sounding circuit 8 and a vibrator drive circuit 9 applies reciprocating motion to the diaphragm 41 of the unit 4. The atmospheric action from the air in the cavity 6 is exerted to the rear side of the diaphragm 41 because a Helmholtz resonator comprising the cavity 6 and the duct 2 is formed to the rear side of the diaphragm 41 and the circuit 9 drives the unit 4 to cancel the atmospheric action. Thus, the volume of the cavity 6 is varied over a wide range without giving any effect on the frequency characteristic of the direct radiation sound. |
