Vacuums are loud

[Llamatron]

If you turn a sound wave upside and play it back it cancels out the original sound almost silencing it.

Why the hell don't they include this technology in vacuum cleaners?

I emailed Dyson once asking about it but I don't remember what they said. It wasn't very positive whatever it was.

[Ethel]

Vaccuum cleaners, lawn mowers - the list is endless.

I don't know why the blessed things have to be so noisy either.

[rojash]

Unless it's a pure sine wave (which a vacuum cleaner surely ain't), turning it upside down won't work. What you need is for every element of the sound wave to be re-generated exactly out of phase. I believe this technology has been used on aircraft flight decks. It consists of an analog to digital converter, a computer with software to analyse the noise and produce a cancelling digital signal, which is then converted to analog, amplified and fed to a loudspeaker. I don't know about you, but I really don't fancy paying for that lot, let alone dragging it around the house when doing the vacuuming :-)

[naz_nomad]

like rojash says .. it'll only work properly with a sine wave ...not the sort of wave you get from a hoover, or lawnmower...

[woodchopper]

Awww Geeees - who bought a dyson ??

[Space]

I don't think the shape of the sound wave has anything to do with it, I think it's about the location of the sound source.

If you want to cancel a sound completely, you have to play the opposite sound at the same location as the noise source, and I suppose that is not physically possible for a vacuum cleaner...

Alternatively, you can wear sound cancelling headphones. It won't cancel the sound completely because others will still hear it, but it will locally cancel it for your ears.

[Llamatron]

It doesn't have to be a pure sine wave, it just has to be a constant noise like a vacuum cleaner or car engine.
I know it's true because I saw it on Tomorrows World many moons ago. ;)

How do noise cancelling head phones work?