space that is the first filler 11 formed of the soft porous material having the low porosity is filled in the space between the back surface of the convex vibrating plate 19 a projecting backward and the inner surface of the back cover 20 and also the second filler 12 formed of the soft porous material having the higher porosity than the first filler is filled substantially along the center axis of the first filler in contact with the first filler as in the case of the embodiment shown in fig1 it is desired that the second filler 12 is filled in a cylindrical shape the front end side thereof is accommodated in the first filler 11 and the rear end side thereof is opened to the outside air at the back surface side of the speaker as described above by combining the fillers different in porosity as described above and filling these fillers so that the fillers are brought into contact with the rear side surface of the vibrating plate 19 a reproduced sound can be prevented from being distolrted due to degradation of air flowability at the center portion of the first filler 11 whereby the frequency characteristic and the transient characteristic can be improved as in the case of the embodiment shown in fig1 the present invention is not limited to the above embodiments and it contains all embodiments which would be easily recognized by persons skilled in the art from the foregoing description within the scope of the object as.