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Preliminary results from a city-commissioned noise study of Juneau in August show aircraft noise here to be less a problem of magnitude than of duration.
The noise stems from a lot of air traffic, according to Paul Dunholter, the BridgeNet sound engineer who revealed the preliminary figures Thursday night at Centennial Hall. His California company monitored noise continuously at 16 outdoor sites throughout the city, 15 other outdoor sites on a short-term basis, and four indoor sites.
"There's not a lot of comparison with other areas. Juneau is very unique," Dunholder said. "When you look at the numbers, levels are lower than at major airports (outside), but duration is longer."
Measuring all aircraft noise during daytime hours 8 a.m. to 9 p.m. showed levels in the city to be above 55 decibels 15 percent to 25 percent of the time. That level represents when an aircraft is clearly audible, Dunholter said.
A decibel is a unit used to express differences in acoustical power. It is a logarithmic function, which means that an increase of 10 decibels for example, from 55 to 65 is double the sound intensity. A decrease of 10 decibels means half the intensity.
The study shows that noise above the 55-decibel level occurred more than 90 percent of the time during peak air traffic hours. Events at the 55-decibel level occurred 100 to 200 times a day.
During daytime hours, levels above 65 decibels twice the 55-decibel level and during which disturbance of conversation starts to occur went on for 2 percent to 5 percent of the time, and up to 30 percent of the time during peak hours. Those events occurred 50 to 120 times per day.
Daytime noise above 75 decibels, representing noise "that is hard to speak above," Dunholter explained occurred 1 percent of the time, and during peak hours up to 3 percent of the time. Those events happened five to 20 times per day.
Kim Metcalfe-Helmar, a long-time critic of the tour industry, asked Dunholter how Seattle's noise level and reaction to it compared with Juneau's.
BridgeNet is conducting a noise study at the SEATAC airport, Dunholter said. SEATAC-area residents "are not happy campers. People who live around Bill Gates want to move (the traffic) to where Paul Allen (a former Gates partner) lives."
Familiar human frailties aside, Dunholter said conditions in Juneau humidity, water surface and topography make it unique and a noisier place than areas that are drier and flatter. Contributing to the uniqueness are the sound frequencies generated by the helicopters and floatplanes, he said. In addition, the duration of local events is considerably longer than at commercial airports.
Flightseeing operator Bob Jacobsen of Wings of Alaska said he thought the data gathered might be useful in comparing quieter aircraft technology with what exists now.
"A couple of years ago, we invested a million dollars in a quieter, nine-passenger Cessna Grand Caravan, now operating out of the airport," he said.
Jacobsen thought and Dunholter agreed the new plane's sound footprint, recorded during the study, could be digitally transferred to the dock area, "so we can compare it to the Otter."
Otters are the twin-engine flightseeing floatplanes that land in and take off from Juneau's harbor. Replacing the Otter's engines with the Cessna's could cut the noise in half, Jacobsen said.
"The study is a step forward it's objective information," said Peace and Quiet Coalition backer Ray Preston.
The coalition put the tourist-flight noise initiative on the Oct. 3 ballot.
"But, as with the Tourism Advisory (Committee) meetings of last fall and the Planning and Policy Committee meeting this February, no dialogue about policy has occurred," Preston said. "I'm afraid this is still the same game of 'let's pretend.' "