PURPOSE: To adjust the stiffness change of the cone paper caused by the temperature change or the aging change by securing the control for the cone tension, and thus to ensure always the optimum acoustic characteristics.

CONSTITUTION: Concave groove 8 opening forward is formed at the entire circumference of outer edge part 6 of frame 5, and thinned circular substance 9 of the elastic material such as the rubber or the like is stuck at the front and outer circumference side of groove 8. The inner edge of substance 9 is adhered to the outer edge of cone 7. Holder plate 12 containing convex streak 11 provided opposing to groove 8 is installed via control screw 13 on the front surface of substance 9 and also at frame outer edge 6. Plate 12 presses substance 9 via screw 13 and between the frame and groove 8. As a result, the tension with which cone 7 is pulled by substance 9 toward direction b can be adjusted.