single fan motors
That's the trend for most vacuums now, one stage, screaming jet sounding motors. I can only think of two canister vacuums that are currently made that have a two stage motor, the metropoliton canisters, and the Perfect metal canister. Apparently you can get the same performance now with some one stage motors, but I really think the two stage motors sound better and are not as annoying, a personal preference of course but a two stage motor does not have to spin as fast to get the same performance. I'm not sure if the motor used in the Sirina is two stage, but it sounds like it is. Most motors used in central vacuums are also two stage as well.