With regard to the noise level, HVI recommends sound ratings of
0.9 sones at low speed and 3.5 sones at high speed. There is no specified
sound rating for Hood A. According to the specification of Hood
B, the sound level is not greater than 1.2 sones for 290 m3/h and
4.5 sones for 830 m3/h. The unit of sone represents a measure of perceived
loudness that is evaluated using sound pressure measurements
in a standard laboratory setting