Why do loud noises seem to hurt? They don鈥檛 seem to cause physical pain but do induce mental anguish. I heard a truck taking on board a bin of empty bottles and the noise was excruciating. I had to get out of earshot.
鈥� Two factors contribute to the unpleasantness of the noise from bottles going into a truck: the volume, and the discordant frequencies. The human ear detects sound using tiny hair cells in the cochlea. A sound wave causes mechanical deformation of these cells, sending an electrical signal to the brain via the auditory nerve. Different groups of hair cells react to different frequencies, with hairs detecting low notes at one end of the cochlear spiral and high notes at the other.
High volumes can damage the delicate hearing apparatus, from chemical exhaustion of the cell-signalling process and mechanical damage. We are adapted to find damaging stimuli unpleasant and painful so that we avoid them.
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Humans also find notes that are too close together very unpleasant 鈥� think of the discord between two adjacent notes on a piano, compared with reasonably pleasant sounds obtained by playing notes spaced apart. This is probably because the closeness of the frequencies means there is an overlap in the groups of hairs activated by each note, overstimulating those that can sense both.
Glass colliding as it is dumped into the truck creates many discords at once.
For high notes, like the crash of breaking glass, the problem is worse because as the notes get higher, the difference between adjacent notes gets smaller, and more hairs will be stimulated by a given note. We are therefore more likely to experience discordance at higher frequencies.
Miriam Ashwell, London, UK
鈥� Rather than the ear damage, the issue here could be hyperacusis 鈥� an oversensitivity to certain types of sound. Some of us might have experienced this during a hangover, when even tiny noises seem dreadful.
Hyperacusis can occur on its own, or as part of a number of medical conditions. As a doctor, I see this most often in migraines.
Having said this, the questioner probably doesn鈥檛 have true hyperacusis. His account sounds more like he has an aversion to that one particular sound. Now my kids are growing up, it鈥檚 wailing babies that set my nerves on edge, giving me the greatest urge to run for the hills.
Robert Ewing, Edinburgh, UK
This article appeared in print under the headline 鈥淐rash, bang, wallop鈥︹��