Dyson gets shit on frequently for being overpriced, but the audible analysis they do one some of their products is crazy complex. Some years ago I watched 30 minute video on the design they did for the hair dryer where they were designing minute angles in the fins of the air impeller, and using a PWM algorithm to measure backpressure in a feed back loop to spin up the fan where it wouldn’t create loud noise while also increasing the volume of air moved. They tuned the mechanisms specifically to shave off tiny peaks in oscilloscope readings.

One thing I remember is that they said they couldn’t entirely eliminate the specific annoying sound frequencies because it had to ramp, but what they did is ramp to right below the annoying sound frequency level, then hold, then burst above the annoying frequency band very quickly. So the operator of the unit doesn’t hear the annoying sound because the device shoots past it so fast.

I’ve never heard of any company be that picky and put so much effort into avoiding one negative experience of a product.

what they did :

“Our product takes in a full blow of air and separates it,” said team member Leen Alfaoury. “Some of that air comes out as it is, and part of it comes out shifted. The combination of these two sections of the air makes the blower less noisy.”

Adds Chacon: “It ultimately dampens the sound as it leaves, but it keeps all that force, which is the beauty of it.”

Their design cuts the most shrill and annoying frequencies by about 12 decibels, which all but removes them, making them 94% quieter.