Originally Posted by
aa777888
For power (not voltage) the conversion from decibels (dB) to linear is y = 10^(x/10) where x is the value in dB. Thus for x = 15dB then y = 31.6. So, no, not even close to "100x quieter".
To go from linear to decibels when measuring power the equation is x (in dB) = 10log(y).
Still worse is that because of the way humans (not machines) perceive sound, each factor of 10 equates to twice as loud or half as loud, depending on which direction the calculation is going. Hence something that is a factor of 10 (10dB) less is half as loud (2 times quieter), and a factor of 100 (20dB) less is a quarter loud (4 times quieter). Thus if this wonderful aircraft is 15dB quieter than a helicopter it is somewhere around 3 times quieter as the human ear perceives things. So very much not even close to "100x quieter"!
Then there is the subtlety of the fact that they use the sound pressure level "A weighted" scale. That's where the "a" on "dBa" comes in. But at this point it's not worth quibbling about how much crazier their numbers are
Thanks for that (and thanks to CGameProgrammerr as well). So as I thought, their claim to be “near silent when in flight” might be a bit economical with the truth, and very unlikely to be “100x quieter”. I’m sure there will still be a lot of prop noise! It’s a bit like people thinking that electric cars are “silent” - they might be at very slow speeds, but at cruising speed they are barely any quieter than combustion engined cars as most of what you hear is road noise.