decibel metre

[bruncher]

Does anyone use a decibel measuring app on their Android phone? I'd be grateful for a recommenation

[scotia]

Yes but for it to be usable it needs to be calibrated against a known sound level

[Weath]

Yes but for it to be usable it needs to be calibrated against a known sound level

Being pedantic it would need to be calibrated against a calibrator.

[kiloran]

Yes but for it to be usable it needs to be calibrated against a known sound level

No, that's for a decibel meter.
A decibel metre needs to be calibrated against a ruler

--kiloran

[Imbiber]

A rule surely?

[AleisterCrowley]

Not if you wanted to calibrate against King Zog of Albania, for example

[Infrasonic]

Pardon?...

You need to decide what weightings are relevant to your intended use and establish if potential apps do them accurately.

[XFool]

Not if you wanted to calibrate against King Zog of Albania, for example

Ah! You mean the standard Albanian measure of length? The 'Zog', I believe.

Possibly there is an accompanying Albania measure of sound level? The 'Zog Bel', the sound level of his Royal Highness, King Zog, sneezing, as measured at a distance of 1 Zog from his royal personage.

[Weath]

Pardon?...

You need to decide what weightings are relevant to your intended use and establish if potential apps do them accurately.

I wasn't being facetious with my early comment of using a 'calibrator'. If a proper sound level meter calibrator is used it will calibrate at a reference frequency of 1 kHz @ either 94 or 114 dB and thus independently cover weightings A, C (which are most likely the ones of interest) Z, and also B and D .

I haven't looked into this for a while, but I never found an app close enough to the professional SLMs I use to give any of them time of day.

[Infrasonic]

Pardon?...

You need to decide what weightings are relevant to your intended use and establish if potential apps do them accurately.

I wasn't being facetious with my early comment of using a 'calibrator'. If a proper sound level meter calibrator is used it will calibrate at a reference frequency of 1 kHz @ either 94 or 114 dB and thus independently cover weightings A, C (which are most likely the ones of interest) Z, and also B and D .

I haven't looked into this for a while, but I never found an app close enough to the professional SLMs I use to give any of them time of day.

No I'd be dubious too.
A decent meter costs an arm and a leg (measurement microphone quality mostly), so I'd very much doubt a phone app could get close.
I've still got my cheap as chips Tandy from the late eighties though as a rough and ready 'gig' meter...

[bruncher]

OK it looks like there's a consensus against using smart phone measurement.

I want to measure 'noise pollution' from aircraft, rail, and road. It seems nothing is simple. There are devices on ebay for under £20. Would I need to do a course on the physics of sound to understand what they don't do that the £420 3M branded device from Screwfix does?

[servodude]

conceptually it's all quite simple, wrapped up in fancy terms

normally sound pressure level (SPL) is measured in what's called dBA (A-weighted decibels)

a decibel is a logarithmic measurement of a power ratio
- it's a tenth of a "bel" but beacuse a "bel" indicates ten times the power it's a bit heavy handed to use normally so we use a tenth of it
- so 10 dB means 10x the power
- 20 dB means 100x the power etc

because this is a ratio not an absolute measurement you need to have a baseline measurement from which to measure your "loudness"
- for sound this means choosing a value of pressure (as sound is just pressure waves) to fix your scale to
- by convention this is 20 micropascals == 0dBA (approximately the lower limit of hearing)

the only other real factor is the "weighting" which is frequency compensation because as humans we "perceive" different frequencies of sounds to be louder for the same power
- or conversely the same pressure of air "sounds" quieter depending on the pitch of the sound
- the A-weighting is an attempt to account for this (https://en.wikipedia.org/wiki/A-weighting)

how does this relate to cheap vs expensive SPL meters?
- precision: good meters can detect smaller changes, across a wider range of frequencies and amplitudes
- accuracy: better meters will have a baseline closer to the specification
- weighting options: dBA isn't the only option
- functions: peak holding, fancy outputs, band selection
- certification

have fun
- sd

[Infrasonic]

OK it looks like there's a consensus against using smart phone measurement.

I want to measure 'noise pollution' from aircraft, rail, and road. It seems nothing is simple. There are devices on ebay for under £20. Would I need to do a course on the physics of sound to understand what they don't do that the £420 3M branded device from Screwfix does?

It depends on what you want to do with the data.
If you need it for legal purposes then there are certain procedures that need to be followed including the use of an expensive calibrated meter to make it all valid.
If you just want it for personal interest then get a cheap meter.

[Weath]

If you need it for legal purposes then there are certain procedures that need to be followed including the use of an expensive calibrated meter to make it all valid.

In which case I would recommended the OP taking on the services of a noise consultant. They know what standards they are measuring against and will have appropriate kit readily at hand.

The mentioned 'expensive' £420 Screwix model is still about 15% the price of the B&K model I have on my desk ....

[bruncher]

If you need it for legal purposes then there are certain procedures that need to be followed including the use of an expensive calibrated meter to make it all valid.

In which case I would recommended the OP taking on the services of a noise consultant. They know what standards they are measuring against and will have appropriate kit readily at hand.

I think this is necessary. How can I find one?

[Infrasonic]

If you need it for legal purposes then there are certain procedures that need to be followed including the use of an expensive calibrated meter to make it all valid.

In which case I would recommended the OP taking on the services of a noise consultant. They know what standards they are measuring against and will have appropriate kit readily at hand.

I think this is necessary. How can I find one?

Have you tried Googling 'noise consultants'?
Warning. It isn't cheap if you go with the commercial consultants. I've used them myself and used to work alongside them when doing the music festivals. The invoices still pain me to this day...

Some of the universities have depts. that do that sort of thing (Salford up my way for instance) so you might be able to convince them to do it as a project to give the students some 'real world' experience. Just bear in mind if you want it to stand up in court it all has to be done to strict procedures, which is always going to be a risk with students unless they have competent supervision.