When a sound signal is received, a sound wave generated on an upper surface of a vibration plate is transmitted to a sound collection portion through a first air passage, and a sound wave generated on a lower surface of the vibration plate is transmitted to the sound collection portion through a second air passage. The sound waves generated above and below the upper and lower surfaces of the vibration plate are about 180 degrees out of phase from each other and substantially cancel each other which minimize or prevent howling.