A horn amplifier comprises a horn and at least one speaker member with at least one spherical sound source; wherein the horn has one throat portion and one voice port opened from the throat portion toward outside, the bottom surface of the inner side of the throat portion of the horn has an open, the spherical sound source of the speaker member connects with the open, the inner side of the throat portion has at least one S-type sound-guide board, the sound-guide board is made as a plurality of paths in order to let spherical sound waves from the spherical sound source of the speaker member enter into the paths, then the spherical sound waves are transformed into plane sound waves, the plane sound waves are delivered to outside through the inner structure of the horn.