Environmental Sound Noise Sensor Module Advice

Thread Starter

DJ_AA

Joined Aug 6, 2021
305
Hi All

I am in need of a sensor module which can detect audio noise outdoors to check if the sound level goes beyond a certain dB level.

I am aware you can purchase a wide range of standalone sensors, but I am looking for any option where I can remotely monitor the values and also store them into some form of cloud storage. This is the reason why I am looking for a reliable module option.

I have seen some ardrino based project, but once would like an option which is more reliable interms of its calibration and stability.

Are there any module solutions, with either a UART or I2C interface?
 

LowQCab

Joined Nov 6, 2012
4,072
Calibration ?, Stability ?,
How high is up ?
Why do You need UART or I2C interfaces ?
What do You intend to use for bullet-proof Internet-Access ?
Do You need "Real-Time" Audio-Streaming ?, Frequency-Response ?, maximum SPL ?, average SPL ?
What must the Data be stored as ?, what File-Format ?
How many hours of Data-Storage before over-writing previous Data ?
What is the purpose of this project ?

A Cell-Phone may do the job with an appropriate App.
.
.
.
 

Audioguru again

Joined Oct 21, 2019
6,691
Much outdoors noise is from "phools" showing off their stupidity by paying mechanics to have their cars, motorcycles and trucks modified to produce more noise than with no muffler. The backfiring sounds like guns. Police catch only a few of them.
What will the noise makers do when everything is electric?

Years ago I used a sound level meter and had a reading of 118dB in a disco.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
305
Calibration ?, Stability ?,
How high is up ?
Why do You need UART or I2C interfaces ?
What do You intend to use for bullet-proof Internet-Access ?
Do You need "Real-Time" Audio-Streaming ?, Frequency-Response ?, maximum SPL ?, average SPL ?
What must the Data be stored as ?, what File-Format ?
How many hours of Data-Storage before over-writing previous Data ?
What is the purpose of this project ?

A Cell-Phone may do the job with an appropriate App.
.
.
.
Thank you for your reply.

The project's purpose is to monitor local traffic noise and building construction work overtime to see the impact it has on the local area.

Well, my preference would be UART or I2C interface, as my PCB, which includes my GSM module, has both UART and I2C available to to my microcontroller. If needed, we could use an ADC. It depends on what is available in the market, as I would like to use something existing instead of creating a new PCB.

The data will be transmitted over the internet to cloud storage once a minute.

I do not need an audio stream but something that reports the dBA. May I can calculate the mean dBA per mean, based on sampling every second and also report the max and min values?

In regard to stability, do the sensors get affected by temperature and humidity or anything else?

Is the calibration factor normally linear?
 

Audioguru again

Joined Oct 21, 2019
6,691
The "A" filter is actually a bandpass filter because in addition to its highpass cutting all irritating low frequency noises, its lowpass cuts high frequencies produced by saws, breaking glass etc.

The "A" filter is usually used with low level sounds and matches the response of our hearing at low levels. Lookup "Fletcher-Munson curves". The traffic noise you are measuring is much louder than low levels.
 

Ian0

Joined Aug 7, 2020
9,814
Thank you for your reply.

The project's purpose is to monitor local traffic noise and building construction work overtime to see the impact it has on the local area.

Well, my preference would be UART or I2C interface, as my PCB, which includes my GSM module, has both UART and I2C available to to my microcontroller. If needed, we could use an ADC. It depends on what is available in the market, as I would like to use something existing instead of creating a new PCB.

The data will be transmitted over the internet to cloud storage once a minute.

I do not need an audio stream but something that reports the dBA. May I can calculate the mean dBA per mean, based on sampling every second and also report the max and min values?

In regard to stability, do the sensors get affected by temperature and humidity or anything else?

Is the calibration factor normally linear?
Do you know the noise regulations for your locality? You will probably need to average the noise level in W/m^2 over an hour and THEN convert to dB, and there will probably be an official definition of what constitutes a "nuisance".
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
305

Ian0

Joined Aug 7, 2020
9,814
Dont know the actual figures.

Doesnt the module output the dBA value?

I found the following module RS485TTL Industrial-grade noise detection module sound detection decibel meter # | eBay

Are these reliable or any good?
It probably does output the dBA value, but it will be the value averaged over a few seconds at maximum. The problem is that the average level over an hour is not the sum of n dBA values divided by n. One has to return to W/m^2 values, average that, and turn it back into dBA. The average of the logarithm is not the logarithm of the average.
You may also find that if you raise any complaint, the authorities will want to see your instrument's calibration certificate before they will take any notice of you.
The value at which it becomes a nuisance is a certain value above the background level, so you also have to measure the background level.
I'm basing this on British legislation, and regulations in your area may be completely different.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
305
It probably does output the dBA value, but it will be the value averaged over a few seconds at maximum. The problem is that the average level over an hour is not the sum of n dBA values divided by n. One has to return to W/m^2 values, average that, and turn it back into dBA. The average of the logarithm is not the logarithm of the average.
You may also find that if you raise any complaint, the authorities will want to see your instrument's calibration certificate before they will take any notice of you.
The value at which it becomes a nuisance is a certain value above the background level, so you also have to measure the background level.
I'm basing this on British legislation, and regulations in your area may be completely different.
How do we calculate the W/m^2 average?

Is this how the standalone sound meters work when they report dBA values?

I guess the calibration would need to be one at authorised lab?

But for basic usage, can you simply preform calibration be simply playing some audio and adjusting it till it reports the same as meter or a good mobile App?

Yes, I am also in the UK, so I guess legislation will take a part when be used with any authorities.

Are there any authroised approved modules or units, where I can simple interface to? I am not looking for something that is serval thousands of pounds.
 

Ian0

Joined Aug 7, 2020
9,814
decibels when used to measure sound are defined as follows:
dB = 10 log (Ws/Wref)
or
dB = 20 log (Ps/Pref)
where Ws is the sound power in W/m^2 and Ps is the sound pressure in Pascal, Wref is the threshold of hearing (1pW/m^2) and Pref is the threshold of hearing in Pascal (20uPa)

The legislation is the Noise Act 1996 for noise made by individuals, or a statutory nuisance under the Environmental Protection Act 1990 for industrial noise with BS4142:2014+A1:2019 defining what the nuisance is. That means that loud music played by an individual is covered by the former, but loud music from a night club goes in the same category as noise from a building site.
Traffic noise is considered background noise and is difficult to complain about, unless it's individual vehicles with exhausts that are too noisy which is an offence under the Road Vehicles (construction and Use) Regulations 1986, and that's a police matter; or you can argue that a new road was installed without the necessary sound barriers, but that wouldn't be easy.

For industrial noise, you are dealing with the noise officer of the district council, and they range from good to incompetent to corrupt (those taking backhanders from the people making the noise).
You'll need some evidence and some measurements. They like calibration certificates although they are completely irrelevant because it is a relative measurement. Microphones almost never go out of calibration, but microphone calibrators drift all over the place. I have one of these: https://uk.rs-online.com/web/p/sound-level-calibrators/1232229 but it's out of calibration. I bet if I checked my microphone the microphone would still be accurate.
The limit at which it becomes a nuisance is 10dBA above background, averaged over an hour in the daytime, and averaged over five minutes at night. (Night is 11pm to 7am in BS4142, but 11pm to 8am in the Noise Act) There are weighting factors for percussive noise. I would advise a visit to your local library to copy a few sections of BS4142:2014 - there are some very good examples of how to apply it.
I would suggest getting a good microphone - this one is adequate and cheap
https://www.behringer.com/product.html?modelCode=P0118
- though probably not quite as good as Behringer claims it might be - and a copy of Audacity. Then make some recordings.
Audacity will work of the averages for you.
You will also need to show where the noise came from. If you have recordings it is much easier to identify what made the noise. The council likes to evade its responsibility by saying that you can't prove what made the noise. If you have a recording of pile-driving, then it's difficult to say it didn't come from the local building site.

Because it's a relative measurement, and errors in absolute calibration are therefore eliminated, a sensible noise office (they are a rarity) would take a recording from an iPad as evidence, provided you have a background noise measurement from a immmediately before or after the noise took place.
With audacity, you can probably edit short lengths of backround noise out from between the nuisance noise.

[Edit] one final point - it's the noise level where it is annoying you that counts. For instance, if you are being kept awake by a night club, then the noise is measured at your bedroom window, not at the door of the night club. It can be as loud as it wants to be if no-one is being annoyed by it.

It must be bothering you if you spent Christmas thinking about it - or was that the only spare time you had to thing about it.
Have a peaceful Boxing Day.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
6,691
The "kids" with their noisy cars, motorcycles and trucks do not bother me in winter because my windows are closed.
But they wake me at 3 o'clock in the mornings in summer.
 

Audioguru again

Joined Oct 21, 2019
6,691
Sound levels have many frequencies and the levels are measured in Decibels. The MIKROE VU meter circuit has an LM3914 IC driving 10 LEDs that measure Volts, not Decibels because the LM3915 IC for Decibels is not made anymore. The specs do not say its variation of output level vs frequency.
Maybe you can connect it to one of their computer systems and program it to do what you need.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
305
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