In a top-secret, padded room at the Dyson research and development facility in Wiltshire, there are several microphone stands at different heights. They could be waiting for the Jackson Five to show up and sing Rockin’ Robin.

But, no: this is a semi-anechoic chamber where new products are tested. It was here that engineers refined the tiny motor that lives inside the handle of Dyson’s new Supersonic hair dryer, launched in Selfridges this week.

The motor impeller was making what its inventor calls “a dreadful racket” until they figured out that if you put 13 blades on it instead of the usual 11, one tone in the motor would be pushed above the audible range for humans. Basically, what I hold in my hand is the first blow-drying tool that doesn’t make your arm ache until it’s about to drop off and can only be heard by Labradors.