How Is The Stereo Sense Of Listening Formed?

- Oct 16, 2018-

(1) The time difference between the sound reaching both ears

Because there is a certain distance between the left and right ears, the sound coming from the front and the back is in danger, and the time from the other directions to the ears is sequential, resulting in a time difference. If the sound source is to the right, the sound must first reach the right ear and then the left ear; otherwise, it must first reach the left ear and then the right ear. The more the sound source is biased to one side, the greater the time difference. Experiments have shown that if the time difference between the ears is artificially caused, the illusion of the sound source bias can be generated. When the difference reached 0.6ms or so, I felt that the sound came completely from one side.

(2) The sound level difference between the two ears

Although the distance between the two ears is not far, the sound level of the sound reaching the two ears may be different due to the blocking effect of the skull on the sound. The sound level near the side of the sound source is larger, while the other side is smaller. Experiments have shown that the larger sound level difference can reach about 25dB.

(3) The phase difference between the sound and the two ears

Everyone knows that sounds travel in waves, and the phases of sound waves at different locations in space are different (unless they are just one wavelength apart). Since the ears have a distance in space, the phase of the sound waves when they reach both ears may be different. The tympanic membrane in the ear vibrates with sound waves, and the phase difference of this vibration becomes a factor in determining the orientation of the sound source. Experiments have shown that even if the sound level and time are the same when the sound reaches both ears, only the change is the same, only the phase is changed, we also feel that the sound source orientation is very different.

(4) The timbre difference when the sound reaches both ears

If the sound wave comes from a certain direction on the right side, you must bypass some parts of the head to reach the left ear. It is known that the diffraction ability of a wave is related to the ratio between the wavelength and the obstacle scale. The diameter of the human head is about 20 cm, which is equivalent to the wavelength of the 1,700 Hz sound wave in the air, so the human head has a masking effect on the sound component of more than a thousand Hertz. . That is to say, the ability of each component in the same sound to bypass the head is different, and the higher the frequency, the greater the component attenuation. Then the tone heard by the left ear is different from the tone heard by the right ear. As long as the sound is not coming from the positive direction, the sounds heard by the two ears will be different, which will become a basis for people to determine the sound source orientation.

(5) Differences between direct sounds and frontal reflection sound groups

The sound emitted by the sound source, in addition to the direct sound that reaches our ears directly, is reflected by the surrounding obstacles one or more times to form a reflected sound group, which gradually reaches people's ears. Therefore, the difference between the direct sound and the reflected sound group will also provide information on the spatial distribution of the sound source.

(6) Differences caused by the auricle

The auricle is forward, which clearly makes it possible to distinguish between front and back. On the other hand, the shape of the auricle is very subtle, and the sounds from different orientations will have complex effects in it, and certainly provide some orientation information.

 

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