Multiplying Air, Reducing Noise
In spite of its luxurious looks and cutting-edge concept, the Dyson fan did have one notable flaw. It wasn't really very quiet. Dyson took note, and decided to revamp the second generation of its Multiplier.
Doing so required a steep investment by the company. Dyson dumped more than $60 million into research and assigned 65 engineers to the project. Together, they created 640 prototypes and filed hundreds of patents, tweaking each design a little more, to investigate the movement of air inside their funky fan.
As you can imagine, part of the noise problem originated from turbulence. The Multiplier sucked air into its base, where it bounced around willy-nilly, creating chaos ... and noise. To pinpoint this noise, researchers placed the fan in a semi-anechoic (soundproof) chamber with 10 microphones listening for every whir and buzz.
Then they built translucent prototypes and passed ultraviolet paint and smoke through the device. High-speed cameras provided frame-by-frame playback, offering visual clues as to areas where air was bunching up and basically causing a ruckus.
Dyson's engineers addressed the turbulence problems by integrating Helmholtz cavities into the fan's base. If you've ever held a seashell to your ear or blown across the top of a glass bottle, you've experienced the effect of these cavities, in which sound bounces and skids across a hard surface.
It's fun to play games with these kinds of cavities. In the right hands, these spaces are also exceedingly useful. On the next page you'll find out why.