Thus, {TAIL ~ the same amount} of air flow may be provided by {HEAD ~ lower speed operation}, so that noise performance can be improved 
Thus , { TAIL ~ the same amount } of air flow may be provided by { HEAD ~ lower speed operation } , so that noise performance can be improved
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH