Determining the orientation of an object helps us to turn our attention to or avoid a sound source, which helps to find a target object or avoid danger, an essential ability for survival. Let’s explore how the auditory system locates sound sources in the horizontal and vertical directions. Localization of sound sources in the horizontal direction depends mainly on the binaural analysis function, i.e., the auditory center decides the location of the sound source by comparing the time and intensity of the sound received by both ears. Let us imagine that if the sound comes from the left side, the sound is bound to reach the left ear first, and after a certain time difference, the sound reaches the right ear, and this time difference is the interaural time difference. Sound waves with a wavelength smaller than the diameter of the head can be diffracted from one side of the head around to the other side, and the longest head diffraction distance is 575 px. With an atmospheric sound speed of 340 m/s, for example, the maximum interaural time difference caused by this distance is about 0.67 ms, which is equivalent to a period of 1.5 Hz of pure sound. The interaural time difference is reflected in the auditory system as an interaural phase difference, and sounds above 1.5 Hz have an interaural phase difference greater than 360. Therefore, the interaural time difference does not provide exact information about the sound source. In fact, sounds above 1.5 Hz do not really form sound diffraction in the head, and sounds above 2 Hz form a head shadow when propagating from one side of the head to the other. The head shadow is the principle behind the formation of interaural sound level difference, which is the acoustic basis for locating high-frequency sound, the size of which varies with frequency. Generally speaking, the higher the frequency, the greater the interaural sound level difference. Sounds above 5 kHz or 6 kHz can form an interaural sound level difference of up to 20 dB, and such a large interaural sound level difference undoubtedly contributes to the localization of these high-frequency sounds. Binaural sound source localization in the horizontal plane depends mainly on interaural time difference at low frequencies, and on interaural sound level difference at high frequencies. The interaural time difference in the middle frequency band does not provide exact source information and the interaural sound level difference is too small, which makes the localization of pure tones in the middle frequency like 2k~3kHz less accurate. The sound source localization on the vertical ground does not depend on the acoustic information of interaural difference, but on the spectral information. In the median vertical plane, the interaural time difference or interaural sound level difference is 0 for all positions, and in the non-median vertical plane, all positions are on a vertebral plane extending outward from the ear, and the interaural time difference or interaural sound level difference at any point on this vertebral plane is a constant, so the interaural difference provides ambiguous acoustic information for localization in the vertical plane or in the anterior-posterior direction, and this vertebral body is called “ambiguous vertebrae”. The uneven surface of the auricle and the mixing of sound waves with their reflected waves formed in the auricular cavity make the spectrum of the original sound waves appear with some characteristic spectral peaks or valleys. Since the formation of reflected waves is determined by the angle of the vertical plane of the sound source, the sound sources in different vertical planes form spectrally different characteristics. Since the localization of the vertical plane source depends on the spectral shape, the source must have a wide frequency band in order to be accurately localized, and pure tones or narrow band noise cause considerable errors in vertical plane localization. In the case of monaural hearing, such as blocking one ear or testing a patient with unilateral hearing loss, the positioning of the sound source in the vertical plane is less affected, while the positioning in the horizontal plane direction is all in favor of the good ear.