SMO — Preliminary results of a test measuring the sound reduction capacity of a muffler on a small airplane are in, and it looks like residents near Santa Monica Airport may have gotten an early Christmas present.
The muffler, manufactured by the German company Gomolzig, took the maximum volume of the Cessna 172 airplane down from 74.7 decibels to 71.4 decibels, according to early results from SMO staff.
That was actually a smaller reduction than measured by community members stationed in the Sunset Park neighborhood, who were using professional sound equipment to measure the noise as a resident would actually experience it from their homes.
“Subjectively, I noticed a significant reduction in the noise impact with the muffler installed,” said John Fairweather, founder of Community Against Santa Monica Airport Traffic, or CASMAT. “It was noticeably quieter.”
More important in Fairweather’s eyes was a different, more complicated, noise measurement that factors in not only the intensity of a sound, but how long a person is exposed to it.
The length of exposure is an important measure in the impact of a noise on the person experiencing it, something that becomes a major consideration with planes flying constantly in a box-like pattern around SMO, Fairweather said.
“With the muffler installed, I could see the plane doing the return leg, but was barely able to hear it above the ambient noise,” Fairweather said.
In the past, Fairweather could hear the plane as it approached on a return leg of its trip — with the muffler that sound was drastically reduced.
The muffler cut the exposure time of a noise by approximately 40 percent, said Susan Cline, assistant director of Public Works, the city department responsible for monitoring the test.
In that case, the reduction in intensity was even greater than the measures of maximum volume, dropping from 82.4 decibels to 77.6 decibels.
Santa Monica is only one of two airports that takes that second, more accurate measurement, Fairweather said.
If a drop ranging from three to five decibels doesn’t sound dramatic enough to earn such community praise, consider what a decibel actually measures.
A decibel is a logarithmic unit that, in this case, provides a relative measure of sound intensity.
The “logarithmic” piece is key — a 30-decibel noise isn’t half as quiet as a 70-decibel noise, it’s actually one-sixteenth as loud, and 70-decibel sound is twice as loud as a 60-decibel noise.
To give some context, a normal conversation can hit 60 decibels, while a vacuum cleaner can climb to 70, according to Purdue University.
The plane used in the test belongs to Joe Justice, owner of Justice Aviation, the largest of six flight schools based at SMO.
Residents upset about airplane noise and pollution have taken aim at the flight schools because counts released by CASMAT revealed that roughly 61 percent of flights that come out of SMO are flight-school related.
If more planes used the mufflers, that could significantly reduce the impact of flights on the community, a Band-Aid solution to address some of the residents’ needs as City Hall approaches 2015, the year that it expects to gain more control over the fate of the aviation-related land at the airport.
There are drawbacks, of course.
The mufflers cost between $4,000 and $5,000 each for purchase and installation, a hefty price to pay for pilots and flight school owners who are not breaking established noise rules as it is.
Justice wonders if city officials can legally ask or even strongly suggest that pilots and airplane owners use the mufflers.
“Hopefully they’re happy with the results,” Justice said. “I don’t know what they’ll do with that other than recommend to people that they do that.”
Neither do city officials, who haven’t yet met to discuss the outcomes of the test, said Bob Trimborn, the manager at SMO.
For his part, Justice doesn’t plan on removing the muffler on his plane, so that’s at least one aircraft out there with the potential to not bother the neighbors.

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