Sound and hearing
Sound : The sound is a mechanical vibration ( an oscillation ) transmit by the air to our ears ( or a microphone ) . The frequency of this oscillation is
expressed by the unit Hertz ( Hz ) that means an oscillation by second . The human ear can understand frequencies between 20 Hz and 20.000 Hz .
Speed : The sound move at a speed of 340 meters by second in the air , what explains the phenomenon of echo and that we see a lightning of storm before to hear it .
The LA : The
frequency of note LA , that serves as reference to tune musical instruments
, is 440 Hz . This is also the telephone’s tonality ( in
The ear: Sounds have a scale of sounding pressure very great . Thereby the ear has a conversely proportional reply per sound volume .
The ear does not understand bass and trebles on the same manner according to the volume of the sound . More the sound is strong more the basses and trebles are heared .
Basses : Bass sounds are channeled by walls ( ground, ceiling ) that increases their relative level ( x2 to x4 ) . The worse places are the corners of rooms .
It is necessary to think at preceding remarks , if we want to make an opinion concerning a sound reproduction , and to listen at a volume equal to the reality .
Trebles : Mediums sounds and trebles are rather directives . They have the feature to be reflected by walls ( reverberation, echo ) .
The ear: The age of a person , or the fact that it has been submitted to high sound pressures , decreases the perception of the sound ( mainly of treble sounds ) .
Tinnitus : A person that has been submitted a long time to heavy sounds has also ears that whistle all the day .
Silence : The perfect silence does not exist . There is always a little noise . In all manner in a total silence we can hear the noise of the blood circulating in ears .