Freak accidents happen all the time, but few are quite as bizarre as the tale of Philip Metzger, a former NASA planetary physicist who almost lost his hearing after dropping a toilet lid.
As detailed in a Twitter thread posted by Metzger last Friday, he was trying to fix the fill and flush valves in his toilet’s rear tank when he dropped its ceramic lid. The tank lid slipped from his hands and struck the rim of the toilet bowl on its way down. The lid didn’t crack, but as it turns out, that made Metzger’s problems even worse.
“The sound stunned me,” Metzger tweeted. “I stumbled out of the bathroom and fell to my knees in the living room, wondering what had just happened. It was surreal. Then I got the idea to test my hearing because I noticed something seemed weird.”
When Metzger spoke, he said his voice sounded as though he “was talking through a kazoo.” To make matters even more strange, when Metzger hummed up a scale, he noticed that the kazoo sound only seemed to occur at specific frequencies that were regularly spaced.
“The stupid toilet lid only fell about eight inches,” Metzger tweeted. “How could it damage my hearing so badly?”
Being a physicist, Metzger was determined to find out. The first step was to look up the speed of sound in ceramic. (Sound travels at different speeds in different mediums.) Metzger told me that the speed of sound in ceramic is similar to brick, so about 4000 meters per second. To determine the frequency of the sound, he then had to calculate the wavelength of the vibration caused when he dropped the lid.
The frequency of a traveling wave is equal to its speed divided by its wavelength, but since the sound wave was occurring in a bounded medium (read: the toilet lid), it generated a standing wave so there are some other factors to consider. A standing wave basically means the sound wave travels from one end of the toilet lid to the other, and when it hits the other end it bounces back.
For Metzger’s purposes, it meant having to divide the speed of the sound wave by the length of the toilet lid, and then dividing this number by two to get the frequency. According to Metzger, this frequency was 3.5 kHz or 3,500 cycles of the wave per second.
Since the toilet lid didn’t break when he dropped it, this meant that all of the energy from that impact was channeled into sound and a little bit of it was dissipated as heat in the lid. The problem is that the lid itself is concave and thus acts like an antenna. This meant that all of that sound energy was directly focused at Metzger’s face and was limited to a few specific frequencies (3.5 kHz and its harmonics).
“The energy travels into your inner ear and the cochlea,” Metzger tweeted. “Since the toilet bowl lid put all the energy into specific frequencies, it was concentrated onto specific spots in the cochlea. Apparently, this concentration of energy was enough to damage the hairs, to bend them over like trampled grass.”
The pressure wave from sound is strongest depending on its frequency, and as Metzger’s luck would have it, his face was close enough to the toilet bowl to receive almost the full power of the sound wave straight to his ear. According to Metzger’s calculations, based on the height from which he dropped the toilet lid (about 8 inches) and a bounce time of 1/20 of a second, then from 20 inches away, that sound has a power of about 138 decibels.
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To put this in perspective, that’s about the sound power of a loud concert or a gunshot heard from 100 feet away. Yet this level of sound power can be dangerous when it is nearby and condensed into a short amount of time and specific frequencies (as opposed to the broad range of frequencies at a concert). In fact, permanent hearing loss from brief sounds happens at around 140 decibels, so Metzger was well within the danger zone.
“What makes it dangerous (in my opinion), is the stiffness of the surface it bounced off,” Metzger tweeted. “The energy was converted into sound in a very brief time making it very intense, and the fact that it didn't break or chip so more energy went into sound instead of breaking molecular bonds.”
When his hearing didn't immediately improve, Metzger spoke to an audiologist friend who said he should go to an ENT physician if his hearing hadn't improved in two days because at that point the damage could become permanent. Metzger said as he approached the 48 hour mark after dropping the lid his hearing finally began to improve.
The whole experience was a shock, to be sure, but Metzger said he’s not quite ready to soundproof his bathroom just yet.
“A safer toilet bowl lid should bust apart on impact, using up the energy by breaking molecular bonds,” Metzger said. “Or it should be a material that isn’t so stiff, so it doesn’t resonate at narrow bands of high-pitched frequencies. But there are bigger problems to solve in life!”