A flat piezo-film speaker is mounted in a motorcycle helmet. The flat-piezo
film speaker is formed from a flat piezo-film curved in one direction to
form at least one curved portion. A radius R of curvature at the curved
portion is larger than at least 200 mm, preferably, in a range of 210
mm.ltoreq.R.ltoreq.360 mm. The piezo-film speaker built into a helmet for
a motorcycle rider is capable of reproducing sound at a sound pressure
sufficiently audible even when running the motorcycle and at a high tone
quality.