combination of both, allows room to work and reduces the blade pass frequency noise by changing the seperation distances. it give you # of blade different frequencies at low amplitude where an evenly spaced blade pattern gives one frequency at a high amplitude. They also use prime number of blades to eliminate multiple orders of frequencies

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)