Right to Quiet Society Noiseletter
Fall 2008 - page 6

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Restaurant noise leaves a bad taste among diners

Re.: Happiness is a good meal.
Restauranteur Meeru Dhalwala links dining and intimate talking, noting that “restaurants are increasingly providing this anointment”. From my experience I would say that dining out is increasingly inimical to good conversation, given the noise levels (apparently encouraged by many restaurant managers who feel that loud noise equals good vibes).

This is true even of Vij’s, Dhalwala’s restaurant, where I last went with friends from out of town whom we hadn’t seen in years. A good opportunity to catch up? Not possible, given the fact that we couldn’t hear each other without shouting across the table. Unfortunately, this seems to be the norm, and “How noisy is it?” has become the replacement question for “Do you have a non-smoking section?” I appeal to restaurants to tone it down.

—Letter to the Editor, The Vancouver Sun, by M. LeGates

The Bamboo Grove Chinese restaurant in Richmond, 6920 #3 Road (across from City Hall) is well visited by mostly Chinese patrons, who chatter very loudly [it's been observed]. Readings taken on June 16 ranged from 68dBA to 76dBA. They asked if we had reserved a table. We hadn’t, but they let us stay for supper. They don’t play background music!

Sound-wave fluctuations help hearing

By Michael Kahn

LONDON – Cutting through the chatter to understand a conversation during a crowded cocktail party is a gift researchers said stems from how the brain distinguishes the pitch of different voices. Scientists call this ability to listen to someone speaking while many others are talking loudly at the same time "the cocktail-party phenomenon," and thought for a long time the direction where the sounds came from was key to doing this.

“What was believed was that the sounds come from different locations in space, and the brain distinguishes from those directions to determine the source of


the sound,” Said Holger Schulze, who led the study.

“We think what the brain is also doing is picking up fluctuations in sound waves. People with hearing aids often struggle to distinguish these sounds in crowds, so the finding published in the journal PloS One may lead to better devices for them," said Schulze, a neuro-biologist at the Leibniz Institute in Germany.

“You could maybe change the acoustic signal to filter out noise the way the brain does,” Schulze said. “If we could implement this in hearing aids to do the job you would not have to do it with your own brain.”

—The Vancouver Sun

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Experts unveil "cloak of silence"

Being woken in the dead of night by noisy neighbours blasting out music could soon be a thing of the past. Scientists have shown off the blueprint for an "acoustic cloak", which could make objects impervious to sound waves.

The technology, outlined in the New Journal of Physics, could be used to build sound‑proof homes, advanced concert halls or stealth warships. Scientists have previously demonstrated devices that cloak objects from microwaves, making them "invisible". "The mathematics behind cloaking has been known for several years," said Professor John Pendry of Imperial College London, UK, an expert in cloaking. "What hasn't been available for sound is the sort of materials you need to build a cloak out of."

"The idea of acoustic cloaking is to deviate the sounds waves around the object that has to be cloaked"

The Spanish team who conducted the new work believe the key to a practical device are so‑called "sonic crystals". These artificial composites—also known as "meta-materials"—can be engineered to produce specific acoustical effects. "Unlike ordinary materials, their acoustic properties are determined by their internal structure," explained Professor Pendry. These would be used to channel any sound around an object, like water flowing around a rock in a stream.

"The idea of acoustic cloaking is to deviate the sounds waves around the object that has to be cloaked," said Jose Sanchez‑Dehesa of the Polytechnic University of Valencia, one of the researchers behind the new work. He believes a material that consists of arrays of tiny cylinders would achieve this effect. Simulations showed that 200 layers of this meta-material could effectively shield an object from noise. Thinner stacks would shield an object from certain frequencies. "The thickness depends on the wavelength you want to screen," he told BBC News.

Dr Sanchez‑Dehesa now wants to make and test such a material in the lab to confirm the simulations. But researchers, such as


Professor Pendry, believe the initial work is already an important first step. "It's not an unrealistic blue-print—it doesn't demand that we do extraordinary things," he said. "This is something that can easily be manufactured." If a material could be commercialised, both researchers believe it could have many applications. Walls of the material could be built to soundproof houses or it could be used in concert halls to enhance acoustics or direct noise away from certain areas.

The military may also be interested, the researchers believe, to conceal submarines from detection by sonar or to create a new class of stealth ships. However, the material may need to be optimised first. "You don't want to wrap a submarine in something that is heavy and several inches thick," said Professor Pendry. "It would add quite a lot to the Navy's fuel bill, I think."

The research builds on work by scientists from Duke University in North Carolina, US, and the Hong Kong University of Science and Technology. Earlier this year, independent teams from the two institutions demonstrated the mathematics necessary to create an acoustic cloak.

Other scientists have shown that objects can be cloaked from electromagnetic radiation, such as microwaves. For example, in 2006, scientists at Duke University showed how a small copper cylinder could be rendered invisible from microwaves. The technique used a meta-material consisting of 10 fibreglass rings covered with copper elements, to deflect the microwaves around the object and restore them on the other side. To an observer it looked like the microwaves had passed straight through the cylinder.
Other researchers hope to build the holy grail of cloaking: an invisibility device that would channel light at wave lengths normally visible to the eye. However, this technology is in a more primitive state, according to Dr. Sanchez-Dehesa. "We believe the acoustic cloak is more feasible than a similar device for light," he said.

—BBC Online

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