Why the sound of nails on a blackboard makes our blood curdle


BY Niamh Anderson


Scientists say the shape of the ear canal amplified certain sounds

MUSIC experts have unlocked the secret of the most horrible noise in the world.

The screeching made by fingernails on a blackboard has been immortalised in scenes from Hollywood movies such as Jaws.

Until now, the reason why the high-pitched scraping noise makes most people flinch has been a puzzle to scientists worldwide.

But a new study says the shape of our inner ear is to blame for the blood-curdling effect.

The research could eventually be used to eradicate or remove altogether the annoying sounds made by vaccum cleaners and other high-pitched machinery.

In a bid to find out why certain noises have such a powerful effect, musicologists asked listeners to rank sounds in order of dislike.

The recordings included fingernails scratching down a blackboard, chalk against slate, Styrofoam squeaks, and scraping a plate with a fork.

The researchers monitored levels of distress in the volunteers, including their heart rate, blood pressure, and the electrical conductivity of their skin.

Listeners ranked fingernails on a blackboard as the most awful of the sounds.


The study found that skin conductivity – a measure of distress – changed significantly when listeners heard the familiar gut wrenching sound.

The offending frequencies were measured to be in the range of 2,000 to 4,000 Hz, the upper range of human speech, which goes from 150 to 7,000Hz.

Crucially, the shape of the human ear canal acts to give extra amplification to sounds in the 2,000 to 4,000Hz range, making fingernails on a blackboard unnaturally loud to the point of being painful.

The researchers, based in Germany and Austria, found that psychology also plays a part in our hatred of the noise.

Some listeners were told the source of the sounds, while others were told that the sounds were part of contemporary musical compositions

Those who thought a sound came from a musical composition, they rated it as less unpleasant than if they knew it actually was fingernails on a chalkboard.

Film-makers have made great use of the noise to get the attention of viewers and put them on the edge of their seats.

In Jaws, shark-catcher Quint, played by Robert Shaw, captures the terrified townspeople’s attention by dragging his fingernails over a blackboard.

The Simpsons parodied the Jaws scene in an episode where Groundskeeper Willie dragged his fingernails across a stained glass window.

In a variation on the theme, The Grinch drags his long green fingernails against a car door in a bid to grab the Who’s attention in the Christmas family flick.

While the frequency of this particular sound can never changed, the musicologists believe that with more reseach, engineers will be able to create hoovers, construction equipment and factory machinery more pleasing to the ears.

Reinhard Kopiez, a musicologist at the Hanover University of Music, Drama and Media, said the research helped musicologists understand why witnessing a performance of music could be more pleasurable than merely listening.

He said: “The audience enjoys the performance because of the knowledge about the [artistic] origins of a sound.”


Movies with Fingernails on a blackboard/hard surface

Jaws – Quint makes his legendary entrance in Jaws by scraping his fingernails on a chalkboard, grabbing the attention of quarrelling townspeople.

The Grinch – The Grinch scrapes his fingernails on a car door when he gets angry about Martha May Who’s engagement to the Mayor.

Final Destination – The salon scene contains some slightly chillingshots of the pedicurist scraping a metal tool along the underside of a soon-to-be victim’s toenail. The sound of the scraping is plainly heard, and unpleasant.

South Park– Mr Garrison uses a rusty nail to write on the chalkboard, because lawsuits have made chalk too expensive for the school.