Weak current College】 【acoustic concepts --- Power By】 【China power house network.

<br> People were able to hear the sound, is due to the Sonic vibration caused by transmission medium (eg air, water, concrete and elastic substance) propagates into the ear. From the sound source or vibration source directly into the ear is called ."direct sound, sound through objects reflection of incoming ear is called" reflection ". Human ears distance approximately 15 ~ 17 cm, this distance makes the ear with a very accurate to determine the characteristics of the sound source position. For example: sounds from .the left to begin entering the left ear, right ear sound than the left ear late its time difference = ears distance / speed of sound, 0.44 ~ 0.5mS. This time difference to listen and feel the sound comes from the left. So direct sound .to distinguish the sound source position plays a decisive role. So when people listen to music with three-dimensional sense and sense of space. In reflections arrive earlier in the ear of Sonic strong, this strong reflection called early reflections, after which the sum of .the reflections are called mixed sound. Ear listening range 20Hz ~ 20KHz. Below the 20Hz called infrasound, higher than the called ultrasonic 20KHz. Sonic vibrations transmitted by the week, the distance is called "wavelength" λ represents the transmission of the acoustic one second .is called the "distance" with a wave speed c represents the Sonic vibration frequency of one second is called "frequency" f represents the relationship between them: λ = c / f sound waves during the transfer process has the role of mutual interference. Two .frequency in the same direction as the same, vibration and coherent sound source produces a sound wave overlapping when there is interference. If they are the same phase, after two waves superposition increases sound pressure strengthened; on the contrary, their phase contrast, after two .waves superposition pressure amplitude decrease, if two wave amplitude, will be fully offset. Because of the interference effects, sound waves often makes space of sound field appears fixed distribution, forming the crest and the trough (from the frequency response curve looks like a comb .filter effect), namely: audio terminology often say - standing wave phenomena. In the Auditorium when due to wall of sound reinforcement of reflection will also appear in Sonic interference phenomenon. If it is a pure tone audiometry (sine wave) signal, such .interference would necessarily be caused spatial sound field of the great differences that have local Sonic will strengthen, some parts of the sound wave will diminish or even completely offset, as the "dead point" (no sound). Fortunately, language and music is not .a sine-wave but complex waveform, this complex waveform using Fourier series expansion is more of a different frequency, different amplitude sine wave. So there is "the" "makeup" effect, so that interference effects are less obvious. But! because different .frequency signal generated by the interference effect, certain frequency signal enhancement, other frequency signal attenuation, often resulting in room transmission characteristics of non-uniform, that is why you want to use the room equalization ". Described by the sounds on the strings of sparse .and dense alternately changing wave, and sparse and dense is air pressure changes, and then through human eardrum to reflect incoming air pressure, thus hear the voice of the brain. Sonic is to describe the sound of physical phenomenon, common waveform representation. All acoustic .have attention! "wave" in nature. The resulting sound conditions for two: 1, must have vibration or oscillation source. 2, Sonic's delivery must rely on the media..