Patent ID: 7300244

Claim:
An apparatus, including: an axial member adapted to rotate about an axis extending along a length of the axial member; a plurality of fan blades positioned circumferentially about the axial member, each one of the plurality of fan blades coupled to the axial member, a first circumferential path length between centerlines associated with ones of a first adjacent pair of the plurality of fan blades is unequal to a second circumferential path length between centerlines associated with ones of a second adjacent pair of the plurality of fan blades, the first and second circumferential path lengths located on a first circumference centered at the axis in a first plane peruendicular to the axis; and a plurality of stationary structures spaced apart from each other irregularly in order to distribute acoustic spectral energy associated with a primary blade-passing frequency (BPF) tonal component of a fan comprising the axial member, wherein each one of the plurality of stationary structures is capable of being pressure-coupled to each one of the plurality of fan blades as each one of the plurality of fan blades passes by each one of the plurality of stationary structures.