Sound level meter notes

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"Can't I just use my smartphone?"
What and how they measure

Sound level meters, a.k.a. sound pressure level meters, decibel meters measures the absolute level of sound, usually referenced to the human hearing threshold.


Note (also from their specs) that they are often aimed at measuring noise pollution in the louder range people care most about. Whether the streets in you neighborhood are crossing local rules, whether your club needs sound isolation, whether your emergency systems is audibile everywhere, whether your industrial workplace is hurting ears (sometimes those may need to go a little higher in loudness than average devices).


Most of these are not to see exactly how quiet your recording room is, because their specs stop around quiet-room levels. Meters that go to such low values exist as well, but are a specific type of product, because they have to care much more explicitly for low-noise design.


Typically:

  • loudness range: ~30dB SPL to ~130dB SPL, usually
measuring levels lower than 30dB SPL is sort of a separate thing, and most purposes for sound meters are probably measuring louder things
  • dynamic range is typically lower (~50dB, possibly less) (so they do some adaptive / configurable gain stuff?)
  • aim for precision is usually < 2dB, and if certified, <1.5 and 1.0
  • frequency range: ~35Hz to 4kHz or 8kHz or such
...the range most relevant to most workplace/industrial hearing damage(verify)
broadly,
for e.g. voice dBA can be more suitable
for noise pollution dBC can be more suitable(verify)
Note that C weighing is relatively flat within 30..8000Hz (it's ~-3db at those extremes)


  • speed
we could measure and display very quickly, but it would be difficult to read off.
sometimes explained as an average over ~125ms or ~1s -- actually it's it's speed of adaptation, a a filter parameter much like τ in RC filters - it'll adjust to much of the difference within this time, and settle only after few multiples.
(sometimes there's also a ~35ms 'impulse', but it doesn't have a lot of uses (other than specifically noticing or specifically ignoring transients?)
Note that a display may update more often than this time parameter - it will still be following the intende curve (which doesn't help you while it's still adjusting - other than to see whether the trend is up or down)


Standards

If your goal is providing a safe work environment, particularly if that safety is due to some regulation, that implicitly requires good precision and certain features.


The meters that meet those standards are more expensive, though probably most of the price lies in the certification, and the fact that you need to regularly send it in for recalibration (which are both part handwork), (and presumably also the fact that manufacturers know you just will pay for it if you need it).


There is IEC 61672-1 (cf. EN 61672, DIN 15905-5) that defines class 1 and class 2 meters. Roughly speaking,

  • class 1 to 1dB, considers a wider frequency range and considers the effect of environment temperature on the measurement electronics(verify).
  • class 2 is precise to approximately 1.5dB


Class 1 is expensive, and typically comes with calibration certification, and you probably won't care about this unless you are required to.

Class 2, when compared to devices that do not mention certification at all, class 2 meters can be significantly better.

Without certification, things can get a lot cheaper. The performance of some is demonstrably close to class 2 -- but without the guarantee.


Where the certified ones start around 1000 or 3000 bucks, you can get a no-gurantees one for 20, and something with the same specs as class 2 without the class 2 certification for less than 100.


Features you may see named

  • Integrating – averaging over time.
Most do, cheap ones may only give you instantaneous values
  • LAeq – A-weighted
  • LCeq – C-weighed (more higher and lower frequencies)
  • LCPeak – C-weighted peak - good to have if you specifically about impact noise (more than a shortish-term average/min/max)


  • octave bands - a coarse way of figuring out dominant frequencies(verify) which can be useful when choosing the most fitting hearing protection
  • LEP,d - daily personal exposure level, roughly sound level times time - and calculated from some samplers rather than measured fully
LEX,8h is the EU name, LEP,d is the UK name
  • separated mic
  • data logging
  • bluetooth/usb logging/readout



Fast/slow, hi/low
Measuring under 30dB SPL