PURPOSE: To obtain a sound field approximate to a sound when a speaker is installed forward by compensating the difference between the lengths of routes until sound reaches both ears of a human being from the speaker by giving the delay time of a sound wave.

CONSTITUTION: Figure illustrates the route difference arising due to a head among sound waves from right and left sound sources. Forward sound waves creat a variety of route differences by an external ear. Main routes fall into (a) on which sound reaches an external auditory canal through a tragus, (b) on which sound reaches the external auditory meatus through a concha hollow, and (c) on which sound reflected in an inside autihelex and reaches the external auditory meatus through the concha hollow. Inner ear type stereo headphones IL and IR are inserted into adapters AL and AR to reproduce a stereo recorded sound. Sound waves emitted from the IL and IR develop hourly delays due to the route difference until they reach ear pads EL and ER through as sound tube.