At normal speed, they are both pretty quiet, as they are only using around 160W, but at full power, the 3.1 is significantly quieter due to the new motor controller using sinusoidal switching, instead of the previous trapezoidal switching. Additionally, the switching frequency of the new controller is now more than double the switch freq of the older controller and well beyond the range of human hearing. There is still some noise from resonance frequencies, but I'd estimate a 70-80% noise reduction in air and even more underwater, since water attenuates higher frequencies more.
The 3.0 is also more efficient and has more thrust while using the same maximum power as the 1.0/2.0, and it will also run at a slower RPM than the 1.0/2.0 for when you barely want to creep along slower than swimming. A USB interface allows the user to make basic changes to min and max RPM, power reduction RPM and activation voltages at low battery, and a few other things, plus we added a LED to the handle, to indicate battery level.
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