I came across several articles (here’s one from FastCompany) in my news reader touting the new improved quieter Dyson Air Multiplier Fans, which all said the same thing – that the new fans are now 75% quieter. That doesn’t make sense. It’s ambiguous. That’s not how we define sound or ‘how loud something is’. And it comes straight out of the press release literature. If it was 100 decibels (dB) before, the new one isn’t going to be 25 dB. No.
Sound and noise levels are rated using a log scale, decibels, or dB. That means that dB’s don’t scale like other scales – it’s not linear.
Sound pressure levels are calculated using the following equation:
- (from Wikipedia)
where pref is 2^-6 Pascals (Pa). Are they talking about 75% quieter in terms of pressure? If so, that’s 12 dB difference. Are they talking about 75% quieter in terms of pressure squared? If so, that’s only 6 dB difference.
And there’s a huge difference between those two levels, subjectively. In acoustics, we have rules of thumb:
– 1 dB change is a just noticeable difference for most people
– 3 dB change is noticeable
– 10 dB change is usually described as “half as loud” or “twice as loud” depending if it’s a decrease or increase in sound level.
So if in fact it is 6 dB quieter, then that’s not really that much – it’s between ‘noticeable’ and ‘half as loud’. If it’s actually 12 dB quieter, then it’s about ‘half as loud’ as before, which would be a pretty decent reduction in the sound level from the fan. Anyways. It’s definitely NOT 75 dB quieter or anywhere near that. Why can’t they just say how much (in dB) it’s quieter?