>>Their design cuts the most shrill and annoying frequencies by about 12 decibels, which all but removes them, making them 94% quieter. The team reduced the overall leaf blower noise by about two decibels, making the machine sound 37% quieter.
Less 37% energy is not 37% less volume to humans.
You won’t be able to tell the difference in volume except for the tone which could be more or less pleasing depending on the frequency they say they got 12db on.
But we humans don't perceive sound energy linearly, so half of the energy is not equivalent to half of the perceived loudness.
The usual rule of thumb is that it takes a reduction of 10dB (1/10th energy) for a thing to sound about half as loud, or an increase of 10dB (10x energy) for a thing to sound about twice as loud.
(This leads to all kinds of interesting problems with making things quieter or louder. It seems superficially implicit that moving from a 100-Watt amplifier to a 1,000-Watt amplifier would be strikingly-dramatic difference, but in an ideal world where everything else is the same then that change only makes things about twice as loud -- the same as moving from a 1-Watt amplifier to a 10-Watt amplifier.)