Thursday, January 13, 2011

Can you hear me now?

kw: book reviews, nonfiction, sound, noise

Alone in an abandoned mine, some five hundred feet from the surface, I shut down the acetylene flame on my miner's helmet and just looked and listened. Of course, I'd been in absolute darkness a number of times, so I was prepared for the phantom lights, phosphenes, that the eye and brain generate when there is no input. But I'd never been alone, with nobody else's breathing or heartbeat or intestinal rumbling to interfere with the deep silence; but there were still my own bodily noises. For part of the time I put my hands over my ears.

I was young at the time, in my early twenties, so I had no tinnitus. The loudest sound was my breathing, which I could stop for half a minute or so at a time. I've consulted several charts of sound levels, and they tend to agree that quiet breathing has a sound level of 10dB (dB means decibels. The "bel" was named for Alexander G. Bell, so it gets a capital letter). If your heart is not racing, its sounds are quieter than that, but perceptible.

This compares with the sound level of ordinary conversation, 60dB. Because the decibel is a logarithm, a 60dB sound has 100,000 times the energy of a 10dB sound. On a slightly geeky note, sound pressure is proportional to the square root of energy, so the pressure on your eardrums from a 60dB sound is about 300 times that from a 10dB sound. The eardrum is quite a wide-range instrument. It takes another 1000x of sound pressure, or one million times the energy, to cause pain, at 120dB.

Your eardrum isn't the most delicate part of the system. The hair cells that transmute sound into nerve signals begin to sustain damage at 90dB, which is why OSHA requires hearing protection wherever the sound level in a work place exceeds 85dB. That's the sound level of an older lawn mower. The newer ones have better mufflers and top out at 75-80dB. Wearing ear plugs when mowing is still a good idea.

If that is the loudest routine sound in your environment, consider yourself lucky. Some years ago, George Michelsen Foy lived in New York City, where he frequently rode the subway. Though he was often irritated by the loudness of the subway trains as they came into the station, he told himself he was used to it. One day something new happened, as he writes in the opening chapter of Zero Decibels: The Quest for Absolute Silence. A local train was stopping in either direction, just as two expresses, also one in each direction, zoomed through the station. In that hard-walled tunnel, he clapped his hands to his ears and barely restrained a scream. Later he measured the sound of one train stopping or zooming by at 105dB. Multiply the sound energy by four (double the intensity), and you add 6dB to attain 111dB. That is the sound level of a punch press lopping pieces out of inch-thick steel.

That event started the author on a year-long search for a really quiet place, one where the threshold of hearing (0dB) would have some meaning. He eventually found, in an anechoic chamber in Minneapolis, a place recognized in The Guinness Book of World Records as "the quietest place on Earth", rated at -9.7dB, in which the ambient noise level is 1/11th of the hearing threshold. In such a chamber, besides heartbeat and breathing sounds, he also heard very thin sounds generated by the hearing system itself, kind of a feedback sound because of the amplification that our ears and brain perform.

For most of us, most of the time, the quietest environment we are likely to experience is in a less-populated area of the public library, where sound levels in the 30-35dB range can sometimes be found. Get too close to the copier machine, however, and the background hum will reach 40dB. It is a testament to the feebleness of a 40dB sound that most commercial sound meters are made to detect sounds in the 40-140dB range. A few more expensive ones can detect 30dB. George Foy bought such a meter, and began, perhaps obsessively, to measure sound levels everywhere. Nowhere in New York City did he find any place with a sound level lower than 37dB.

He tried finding silence in the countryside, such as the Berkshires in Massachusetts. It takes a pretty still day for the wind noises to be quieter than 35dB. One bird chirping, and you're back in conversational range, 50-60dB! Though he never tells us how quiet a snowy country day is, I've read elsewhere that, if you are the first one outside after a 1-foot snowfall, the sound level can drop below 10dB. You have to be pretty far from the nearest active roadway…

He moved his family to Cambridge, Massachusetts. The background noise level was not that much different from NYC, but the trains weren't quite as loud. More importantly, the kinds of sounds were different, and he began to realize that quality means as much as quantity in sound, also.

Foy visited people known for silence, such as the Native Americans of the Southwest. They value silence whenever there is no reason to speak. He found it can drive a more gregarious Anglo rather nuts. The pauses after their sentences were so long he was never quite sure when someone was finished speaking.

He visited the Neutrino Observatory near Sudbury, Ontario. Though the Argon tank there is remarkably free of electronic noise and radiation, the equipment that maintains it kept the acoustic sound level in the range of 65dB. Apparently, sound doesn't affect neutrinos.

He even visited the Trappist Monastery at Cîteaux, France, where the monks speak so seldom that some almost forget how. He interviewed a leading monk who is allowed to speak with "outsiders" at specified hours, and found it as disconcerting as speaking to a Sioux elder.

What is silence, really? He considers that silence marks boundaries; words and sentences are preceded and followed by short silences. The more gregarious a person, the shorter those little quiet spaces become. Silence also precedes ideas. But Westerners tend to denigrate the "idea people", and look down on those who are "too quiet." In modern culture, silence is treated as though it were as dangerous as the vacuum of outer space. While some office spaces (my own workplace included) are remarkably quiet, retail establishments are typically filled with sound, including Muzak, the buzz of cash registers, and the nearly continuous chatter of gregarious sales clerks. Young people (such as my son) keep an iPod going whenever they aren't playing a video game or watching a TV show (whether online or on a real TV). They frequently talk while all these things are happening. My generation tends to watch a show in near silence, and we don't have the TV's volume up very high, either.

At the very end of his quest, the author attends a two-day retreat of silent meditation. Now he knows that complete silence is unattainable. But relative silence has its uses. It allows you to pay more attention to the sounds you cannot control. It lets more of your thoughts reach a conclusion. Even in the quietest retreat center in the forest, there are many small sounds and each tells a story. With our evolutionary history, no matter what we are listening to, we are also listening with more than half an ear for any sound that might portend a predator on the prowl. As the retreat draws to a close, he is longing for a certain sound, the welcoming yell of his children when he returns home. The sound meter has done its work, and he is done with it.

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