PURPOSE: To attain reproduction with good sound quality by forming two faces of a horn opposite to each other so as to be changed for folded angle with four hinges thereby changing an output sound pressure characteristic and a directional characteristic and matching the speaker for a condition of a room to which the speaker applied.

CONSTITUTION: Both wall faces c, d above under the horn A opened in the front face of a rectangular ribbon diaphragm are horizontal parallel faces. Both left and right wall faces a, b of the horn A are formed by a plastic, and four longitudinal thin parts a1, a2, a3, a4, b1, b2, b3, b4 are formed from a part called a nozzle or a throat being an open base of the horn A to the open end part symmetrically, and they are formed as a hinge so that the folded angle at this part is changed freely. Thus, the horn shape of both the left and right wall faces a, b is made variable.