# “It’s now 75% quieter” What the heck does that mean?

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:

$L_p=10 \log_{10}\left(\frac{{p_{\mathrm{{rms}}}}^2}{{p_{\mathrm{ref}}}^2}\right) =20 \log_{10}\left(\frac{p_{\mathrm{rms}}}{p_{\mathrm{ref}}}\right)\mbox{ dB} ,$(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?

## 7 thoughts on ““It’s now 75% quieter” What the heck does that mean?”

1. Tze says:

Because the average person won’t understand what 75 dB means but marketing it as 75% quieter appeals/applies more to the general public? 🙂

1. Yeah but can anyone actually tell you what it really means subjectively either? Say we give someone a radio and control of the volume knob – would they be able to show you what 75% quieter is? Also, what about 100% quieter? Or for that matter, what is 75% or 100% louder?

2. Art says:

They also used 10 microphones to “measure” sound power. I agree with Tze, they have to use a generic marketing term like 75% to make any kind of sense to the general public – even if it isn’t clear on what it actually means acoustically. Logically, I think 75% reduction would have to relate to subjective loudness. i.e. 50% reduction would equate to a drop of 10 dB.

Most easily achieved would be a 75% reduction in Pascals correlating to a 6 dB drop so that is probably what they meant.

1. I think smart companies educate their clients (buyers of their products or services) And part of that is being clear about what they mean. Find some way to explain it in clear laypersons’ terms and not vagueness and hand-waving. Dyson must have a huge marketing team/budget that can figure it out.

1. Art says:

It’s like you said before, for such a subjective issue, is it even possible to explain it clearly? I think subjective loudness is probably your best bet but beyond “double” or “half” I don’t think any other terms would have much meaning. Maybe they should just say it is “noticeably quieter”.

2. If it’s 6dB quieter: “Our new fan is so quiet, it would take 4 new fans combined to make as much noise as our older fan.” Or something along those lines. Compare it to other things. “Quieter than our Dyson hand dryer,” or “As quiet as a city bus.”

3. Art says:

4 fans vs 1 is a pretty good way to get the information across. Not necessarily better from a marketing perspective though. Although we all know that great marketing isn’t directly tied to telling the whole truth. Also I don’t know what kind of new-fangled hippy buses you have in Ottawa, but here in Calgary you would say “as NOISY as a city bus”.