Why Sounds of Nails on Chalkboard is not unpleasant to Everyone?

[Sufiyan]

In order to get my question , first read this please,

Michael Oehler of the Macromedia University for Media and Communication and University of Vienna's Christoph Reuter, whose new research into the unpleasant sound may have found the root of our dislike.

In their research, the two musicologists looked at both physical and psychological reactions to unpleasant sounds.

The most impressive results came in the physiological measurements taken by the researchers. They found a dramatic change in skin conductivity when unpleasant sounds were played, showing a distinct physical reaction to the sound. The researchers also pinned down the frequency range of skin-crawling sound to between 2,000 and 4,000 Hz — which is the same range as human speech. Amazingly, when these frequencies were filtered out and the sound replayed, participants had no trouble listening to the sound.

The range of frequencies for unpleasant sounds is also important because of the structure of human ears. Our ears are shaped in such a way that they amplify frequencies between 2,000 to 4,000 Hz. The researchers believe that the chalkboard sound, and similar tones, are unbearable because the amplification is so great to the point that it becomes painful.

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 ? Am i right ?

If that is true, and every human has its ear designed to amplify sound ranges from 2,000Hz to 4000Hz frequency then why such sound 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 ?

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 why these sounds are not unpleasant to everyone.

Edited September 23, 2012 by Sufiyan