PURPOSE: To flatten sound pressure characteristics through reducing attenuation in a high frequency range and to decrease directivity, by coupling with a horn driver part a horn whose internal sectional area varies according to a specific function or whose horn-side wall shape is varied according to a specific function.

CONSTITUTION: A horn whose internal sectional area varies as shown by equation I or whose horn-flank shape is expressed by equation II is used. The horn is coupled with a horn driver part to reduce attenuation in a high frequency range, thereby flattening sound pressure characteristics and decreasing directivity.