A sister company of Google, Alphabet’s Wing Aviation, just got federal approval to start using drones for commercial delivery. Amazon’s own drone-delivery program is ready to launch as well. As drones take flight, the world is about to get a lot louder – as if neighborhoods were filled with leaf blowers, lawn mowers and chainsaws.
Small recreational drones are fairly loud. Serious commercial drones are much louder. They have eight or more propellers (Alphabet’s Wing has 14; Amazon’s Octocopter has eight spinning at thousands of revolutions per minute, physically beating the air to generate lift and movement. The heavier the load, the harder they have to work, the more air gets beaten – and the louder the sound.
Drones also make higher pitched buzzing sounds than helicopters, which have much lower frequencies because their larger rotors don’t need to spin as fast to generate the necessary power. Now imagine tens or even hundreds of drones buzzing around your neighborhood, delivering packages to homes and businesses. Next, imagine the round-the-clock hives of aerial activity that warehouses and distribution centers will become, in addition to their existing burden on local roads; Amazon recently ordered 20,000 new vans.
Will there be a weight limit on delivery-drone payloads? Who will monitor the sound levels, and how? Should there be a curfew on hours of operation? There must be a reason companies don’t include the sound of the drone in advertising materials – and it’s probably not because they sound so nice.
Health and well-being
Urban designers are often concerned about sound levels in neighborhoods. Wealthier suburbs, for instance, are always farther from big noise sources like airports and highways. Existing noise-control laws are basically useless at protecting people’s well-being, general health or mental health. Some wealthy neighborhoods even consider planting trees not just for the added greenery but because the soft foliage absorbs sound, making these communities even quieter and more peaceful.
Incessant mechanical buzzing doesn’t fit with anyone’s idea of a pleasant community. That’s what drones will bring, though. Even domestic drones can raise baseline sound pressure levels by at least 20 decibels; when each 6dB increase means loudness doubles, that means a single drone can make an area 8 to 12 times louder than it is now.
It’s not just loudness. Drones have relatively small propellers, which don’t move much air, but they move it very rapidly. The amount of energy put into moving the air equates to its volume or loudness. The speed of the spinning equates to its pitch, or frequency. Refinements to propeller shapes can change the pitch, but companies will only research noise reduction if their customers demand it.