Montblack writes:

Not sure if Honda's "GE-Honda" HF118 Turbofan Engine qualifies as
'high-bipass'
...it is extremely quiet.

You can usually recognize high-bypass fans because they are quite fat
in front (because of the large fan), and often the nacelle has two
salient parts, a fat part in the front and a thinner part in the back.

They are quieter because the flow of air from the fan acts as a buffer
between the noisy flow from the exhaust and the surrounding air. They
are also more efficient than turbojets at high subsonic speeds. I
think there is at least one supersonic turbofan design, but I don't
know to what extent they are used for this in production aircraft.

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