Abstract: [Problems]To accurately tune the vibration frequency of a suspension during assembly. [Means for Solving Problems] Secured positions 3e where a magnetic circuit part 2 is secured to a suspension 3 are provided near to each other. From among the secured positions 3e, secured positions 3e suitable for the characteristics of a suspension 3 to be mounted and the weight of a magnetic circuit part 2 are selected and secured to each other. Thus, the distance between the securing position and the central position of vibration of a suspension 3 and a housing 1 can be changed to tune the frequency to the desired value.