Scratching The Blackboard Sound

There are certain sounds in life that are pretty much universally hated. Chalk on slate, styrofoam squeaks, a plate being scraped by a fork, and the good old fingernails on blackboard all cause a small amount of personal agony, regardless of culture or location on the planet. Not surprisingly, this reaction can be measured with increased heart rate, blood pressure and electrical conductivity of the skin.

Believe it or not, a lot of time over the last century has actually been spent trying to determine why this happens. Now a new study conducted by musicologists at the Macromedia University for Media and Communication in Cologne, Germany, and the University of Vienna seems to have found the answer.

What they found is that the frequencies involved with unpleasant sounds also lie firmly within the range of human speech — between 2,000 and 4,000 Hz. Removing those frequencies from the sound made them much easier to listen to, but interestingly, removing the noisy, scraping part of the sound made little difference.

This meant that there is actually a powerful psychological component at work as well. If the listeners knew that the sound was fingernails on the chalkboard, they rated it more unpleasant than if they were told it was from a musical composition. Even when they thought it was from music, however, their skin conductivity still changed consistently, suggesting that the physical part of the response remained.

Still, the real question is, why do we have such a reaction to the noise? It turns out that the physical response is likely generated by the shape of the human ear canal, which amplifies frequencies in the range of 2,000 to 4,000 Hz. The researchers determined that when a screech on a chalkboard is generated, the structure of our ear takes that narrow band of frequencies that are already loud and amplifies them even further, making us want to jump out of our chair. Seems so simple now, doesn't it?

So while that mystery seems to have to unveiled, there are a still lot more unpleasant sounds to be explored. Why bother, you might ask? Because the eventual goal is to try to mask those frequencies within factory machinery, vacuum cleaners or construction equipment to minimize any hearing damage. For the time being, though, it’s probably best to steer clear of blackboards, and be careful when you boost at 2k to 4k!

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