Are you not irritated by the sound of screeching of nails on the blackboard? It could be a mattress or a wall too. It’s one of the most annoying things that I can think of. How much ever I hate it, the engineer in me wants to research on it. I wish to conduct an experiment and I look forward to your suggestions.
It seems like it has definitely got something to do with some frequencies that human ear is more sensitive to. We need to experiment a lot. One place where you can subject your ears to all kinds of frequencies, is a rock band concert. If you have been to one, I am sure you can think of this one moment during the show when the instruments are being tuned and that noise pierces through your body. This makes me more certain of the existence of these irritating frequencies that cause all the pain to our ears.
If I take a more cynical approach towards studying sound, I should be focusing on sharpness and roughness. While sharpness is directly proportional to high frequency components in the signal, roughness is more about fluctuation in the intensity of the frequency components. Another important clue is that screeching hurts more when done on rough surfaces, like chalkboard and rough cushion covers. If you take a microscopic view on our nails scratching on rough surfaces, then the contact between nails and board will constantly make and break because of the irregular surface and this can account for fluctuations in the intensity of frequency components. Thus, I suspect that the roughness element in sound is the main cause of this pain in the ears!
However, I wish to conduct an experiment using Audio Data Acquisition Card and LabVIEW Signal Processing libraries. I look forward to your suggestions in setting up the testing environment.