How does the human ear distinguish between front and back and up and down?

Nowadays, there is a relatively mature sound positioning algorithm in the industry, called head related transfer functions (abbreviation: HRTF), which mainly uses algorithms to convert a single sound source into two channels to deceive the human ear for positioning.

The exact principle is explained in great detail on the wiki or elsewhere. To put it simply, when a sound is emitted from a certain location in the space, it will be transmitted to the two ears separately, passing through the pinna.

and isoreflexes, eventually reaching the tympanic membrane.

There will be a time lag between the arrival of these two sounds.

This is a major factor in human positioning. As for the specific directions such as up and down, front and back, it is mainly the sound passing through the pinna and the external auditory canal.

and many other places of reflection and filtering. This ability to distinguish is highly individualized, each person has a different ear canal, pinna, and even a skull size and shape, and everyone's ability to localize sounds is trained over a period of time. For example, when an ear injury is cut off, the person's ability to localize sounds will be impaired, but after a period of adaptation, they can still return to normal.

Whether it is from experimental results or human experience, one simple conclusion can be drawn that the nervous system can determine the position of a sound source in the horizontal direction by comparing the time difference (ITD) and the Interaural intensity difference (IID) between the same sound source reaching the ear. More detailed studies on the spatial positioning of the human ear (including horizontal positioning and vertical positioning) show that in the case of low frequencies (below), it is mainly ITD that plays a major role in sound localization; In the case of intermediate frequencies (range), it is mainly the ITD and IID that work together; In the case of medium and high frequencies (in the range of 4kHz-6kHz), it is mainly IID that plays a role; In the case of high frequencies (above 6 kHz), it is the interference effect caused by the scattering of sound waves by the pinna.

However, whether it is a sound source in the vertical direction, or directly in front of or behind it, it all has the same characteristic – that is, it does not provide a signal of binaural difference. How is such a sound source localized by the human ear? On the one hand, due to the structural principle of the human body, the sound that can be received by the human ear will be affected by the structure of the pinna, shoulder and head - in the process of propagation, some sounds will be diffracted and scattered when they are blocked by the human body, and interfere with the sound directly reaching the ear canal at the position of the ear canal opening, thus affecting the sound spectrum entering the human ear; The human ear unconsciously twists its head to determine the location of a sound source—and this process creates a certain amount of binaural disagreement cues (e.g., when the sound source is directly in front of you, slightly twisting the head to the left will bring the right ear closer to the sound source, and a certain ITD and IID will form between the left and right ears), thus helping the human ear locate the sound source.

Yes. From the binaural effect, it is impossible to distinguish the sound difference between the two ears without distance difference, and it is impossible to accurately determine the location of the sound source. At this time, you can turn your head so that there is a difference in distance between the two ears to determine the position of the sound source.

The landlord's greeting is very good, I wonder if people have three ears (on the top of the head facing backwards), whether they can distinguish the front and back.

The main thing is the poor utilization intensity.

It is the strongest that is directly facing the ear piercing.

So from time to time, people will turn their heads left and right to determine the source of sound more accurately.

In fact, if you can't turn your head, you have a much lower ability to determine the sound source in the middle profile of the person.

If the headphones are worn upright, the stereo sound can be reproduced by the different volume levels of the two ears, but it is difficult to distinguish between the front and the top. In fact, this kind of stereo sound assumes that the sound source is at the level of the ear, not up or down. If you want to listen to true stereo sound (being able to distinguish between top and bottom), you must have multiple sound sources in each ear of the headphones.

In anatomy, the ear is made up of three parts: the outer ear, the middle ear, and the inner ear.

The external ear includes: the pinna, the external auditory canal, the nerves of the external auditory canal, and the blood vessels.

The middle ear includes: tympanic cavity, eustachian tube, tympanic sinus, mastoid process.

The inner ear includes: vestibule, semicircular canal, cochlea, internal auditory canal, middle cranial fossa, and petrous temporal bone.