Naked Science Forum

Non Life Sciences => Technology => Topic started by: jazzyman on 24/07/2017 10:55:17

Title: How accurate are sound monitoring apps for mobile devices?
Post by: jazzyman on 24/07/2017 10:55:17

I have just installed a sound monitoring app onto my phone and I am not sure how accurate these apps are. In a quiet room the meter is displaying 32db, does this figure seem correct? I would have thought that it would have been a lot lower?

When I use an electric fan which is rated  by the manufacturer to be 60db the sound reading goes up to 45db, which is a 13db increase higher than the initial 32db figure.

If the normal sound figure is correct i.e. 32db should the figure rise to 92db when the electric fan is operating?

Title: Re: How accurate are sound monitoring apps for mobile devices?
Post by: Colin2B on 24/07/2017 11:31:49

Are you taking the measurement at 1m from the fan? Also unless you are using a special calibrated reference microphone you can't rely on accuracy, just a guide. However, 25-30dB isn't unusual for what appears to be a quiet room, remember your ears adapt and filter out much of the background noise.
Sound levels are logarithmic so don't add arithmetically
Use this rather than formula https://www.noisemeters.com/apps/db-calculator.asp

Title: Re: How accurate are sound monitoring apps for mobile devices?
Post by: Bored chemist on 24/07/2017 11:37:02

And you need to make the measurements either in an anechoic chamber or a an empty field to stop reflections influencing the results.

Title: Re: How accurate are sound monitoring apps for mobile devices?
Post by: evan_au on 24/07/2017 11:47:58

Quote from:  jazzyman

In a quiet room the meter is displaying 32db, does this figure seem correct?

Wikipedia lists a "very calm room" as being 20-30dB, so that is quite reasonable.

See: https://en.wikipedia.org/wiki/Sound_pressure#Examples_of_sound_pressure

Quote

When I use an electric fan which is rated  by the manufacturer to be 60db... should the figure rise (from 32dB) to 92db when the electric fan is operating?

Decibels (dB) are a logarithmic scale, so they don't "add up" the way "normal" numbers do.
Decibels represent relative sound levels, not absolute sound levels, as this is the way that human hearing works.

If you double the sound power, the sound level goes up by 3dB (10log₁₀2 = 3.01).
- If you double the sound power in a very quiet room, the sound level will increase from 32dB to 35dB
- If you double the sound power in a moderately quiet room, the sound level will increase from 45dB to 48dB
- a 13dB increase represents a 20x increase in sound power  = 10^1.3. At this level, you can ignore the noise contribution of the original room.
See: https://en.wikipedia.org/wiki/Decibel

Quote

an electric fan which is rated  by the manufacturer to be 60db the sound reading goes up to 45db

There are conventions about how sound levels are measured - for example, it is normally measured at a distance of 1 meter, and with a frequency weighting representative of human hearing (eg A-weighting).
They will normally quote a maximum sound level, when the fan is set to its highest speed setting.
See: https://en.wikipedia.org/wiki/Sound_pressure#Examples