In order to get my question , first read this please, So it means that when the sound is produced from nails on the chalkboard, the frequency range of this sound is between 2,000HZ to 4,000HZ with the amplitude of the sound is mostly a noise ? and human ears are designed to amplify this range of frequency, which is why the sound is unpleasant to our ears ? If that is true, and every human has its ear designed to amplify sound ranges from 2,000Hz to 4000Hz frequency then why such sounds isn't unpleasant to everyone ? Does it mean that not every ear is capable of amplify these frequency or every ear is trained to amplify the range of the frequency according to the environment they have grown from their birth ? There are certain other sound which specifically unpleasant to some people and other sounds to other people like when we try to cut the silk yarn or silk cloth from our teeth and it slips out from our teeth the sound which is produce is highly unpleasant to some of the people. Another example is the sound of any pointed tip tool on the zigzag surface. These sounds are not unpleasant to everyone rather it is unpleasant to some of the people. If every ear amplify the same frequency range of 2,000Hz to 4,000Hz and if these sounds are mostly the noise then why these sounds with noises doesn't affect everyone's ear ?