MEASURING HIGH NOISE LEVELS

The Campbell Associates team recently went to a clay pigeon shooting range as part of an experiment to capture accurate high sound pressure levels. They took measurements from various shot guns at a distance of 0.5m from the trigger, using a sound level meter (see picture x).  This type of measurement is sometimes required to assess the hearing protection used by individuals participating in gun related leisure activities.

The sound level meter used was a Norsonic 140 sound Analyser and was tested in three configurations.

1. The standard meter which has a 140dB full scale range. 
2. The standard meter in high level mode which boosts the full scale range to 150dB.
3. The standard meter with a quarter inch high level microphone capsule.  This increases the full scale measurement range to 160dB.

The Results:

1. In the standard mode the system frequently overloaded when the microphone was positioned closer than 1 meter from the gun being fired.

Figure 1.

1. How does a high range option work – How do you get an extra 10dB from a standard ½” microphone?

When the extended measurement range is activated the standard 200v microphone has its polarization voltage lowered.  This is reduced from 200 V to about 70 V. The microphone sensitivity will then be reduced by 10 dB and the instrument will be able to measure peak signals up to 150 dB. The change in the polarisation voltage will lead to a small change in the frequency response for the microphone. This change is automatically compensated when the extended measurement range is selected. Corrections are specific to each microphone type and should not be mixed.

With this option activated in the sound level meter most measurements were achievable.

Figure 2

However at a distance of half a meter from the gun with heavier shot the sound level meter did see overloads with measured levels over 150dBc peak.

1. Using a quarter inch microphone

With an adaptor, a ¼” microphone will fit onto a standard half inch preamplifier and you can then measure levels with a standard sound level meter.With this microphone it was possible to measure peak levels without overloads with the highest peak of 157.9dBc

Figure 3.

Why quarter inch microphones?

Quarter inch microphones are inherently lower in sensitivity than ½” microphones.  The smaller surface area means the microphone diaphragms are less flexible and the same sound pressure impinging on them leads to less voltage coming from the capsule.  This reduced voltage is desirable for very high sound pressure measurements as it is high signal voltages that lead to overloads!

How to measure beyond 160dB?

1/8th inch microphone – This allows measurements to 175dB.  With a 120V preamplifier supply it can measure to 178dB.

Preamplifier voltage – For extremely high sound pressure measurements it is important to not only have a microphone with low sensitivity; you must also have a preamplifier which can handle high signal voltages to avoid clipping of the signal. For your sound level meter (or PC analyser) to display accurately these measurements a preamplifier with a 120V supply is preferable.

Artificial intelligence is all around us, in the car, at home and possibly in the workplace, with services such as Siri and Alexa making life easier.

Using AI, Sonitus Systems have developed their audio capture option to accurately identify noise sources. No longer must site staff listen to noise recordings to establish the cause, ANI does it for them! The updated Sonitus Cloud system, powered by Amazon webservers will intelligently analyse each recording, to identify what type of noise it is. Audio recordings are labelled with their noise type and each category is quantified in clear and simple reports, ready to quickly and easily explain a noise breach. And to keep site staff fully informed, email alerts are sent every time a recording is made, or a trigger breached. All recordings can be played back on a smartphone, PC or tablet.

ANI – Automated Noise Identification is a game changer for demolition and construction site staff.

Noise identification is a problem for remote monitoring of construction and demolition sites because, without a human ear at the measurement point 24 hours a day, it can be difficult to establish the actual source of a noise breach – ANI solves it.

Construction sites situated in cities are normally surrounded by lots of non-related noise such as vehicle traffic, sirens, horns, bird calls, motorbikes and people, which could negatively affect the readings and the noise limits imposed on the site – ANI solves it.

If you are interested in hiring or purchasing a Sonitus Systems EM2030 noise monitor or SiteSens combined noise and dust monitor, contact us today.

Is your environmental monitoring equipment regularly calibrated?

Noise, Vibration and Dust monitoring data is valuable proof that your environmental protection procedures are effective and gives you the evidence necessary to defend your position should a complaint be raised against site activities.

BUT

For environmental monitoring data to have any credibility, the recording equipment used must be calibrated in line with the manufacturer’s recommendations. And to ensure the data is submissible in court, the calibration laboratory must be UKAS accredited.

Lengthy and expensive site closures are a real possibility if the monitoring data you provide to defend your position to a local authority, comes from uncalibrated equipment.

Without a current calibration certificate, the investment in your equipment, operating processes, staff training, data analysis and efficient time management could be wasted.

Campbell’s calibration service is designed to make your life easy; we offer a hassle-free process to get the job done, and with 4 dedicated laboratories it’s quick.

How it works – 3 simple steps

1. We send you a calibration reminder

2. You contact us for a quotation

3. You email us your purchase order

And we take care of the rest

• We collect monitors from site and reinstall them once calibrated

We can supply hire kit to avoid down time, at greatly reduced rates

• Multi-unit calibration discounts offered as standard
• 4 UKAS accredited laboratories provide a fast turn around
• Digital certificates are stored in your own cloud portal

Calibration Management Portal

To make our calibration service even more efficient and to eliminate the age old

problem of lost paper certificates and forgotten equipment details, we have developed our

Calibration Management Portal. On this digital platform each customer has a password

protected account, for instant access to certificates and up to date equipment records.

For your convenience

• Digital certificates are automatically loaded to the cloud for secure storage
• Calibration quotations can be requested with just one click, using pre-stored information
• Environmental monitoring calibration service is made easy here at Campbell Associates.

I’m Emily, your calibration advisor.

For all enquiries, quotations and bookings please contact me on

emily@campbell-associates.co.uk 01371 871 030

John Campbell and Martin Williams have investigated and written up their finding in this fantastic article about low-cost sound level meters and their claim to meet IEC61672.

It can be tempting to buy the cheapest tool for the job, especially if it claims to meet all the relevant requirements. But can these claims be trusted, should the buyer take these statements at face value or with a heavy pinch of salt?

Six low-cost sound level meters were randomly selected and tested at two independent, accredited ISO 17025 UKAS laboratories. All six meters failed at least one test, with a number failing multiple tests and basic requirements for providing the relevant information to perform a periodic test.

READ THE FULL ARTICLE BELOW

How much is our hearing actually worth may June2021 – Download PDF

In conclusion: All meters failed at least one test; some failed several tests, including linearity, frequency weighting and especially tone burst, which five of the six failed. One meter was close to passing all tests.

Each meter was advertised as being compliant with IEC 61672, which would indicate that they should meet the stringent requirements of this standard, and should pass all the tests detailed in part 3. Meters were purchased new, and immediately submitted to periodic testing per IEC61672-3, at two test laboratories. Four units failed to provide the required information in the user manual needed for a calibration check to be properly performed. In each case the manufacturer, upon request, was unable to provide the necessary information. One manufacturer did acknowledge the requirement and removed from their marketing, all claims to IEC61672.

According to the standard, testing should not normally be performed. However, for this exercise tests were made and failure of the manufacturer to provide compliance information meant that some of the tests were not accurate, as additional uncertainties were introduced. This is shown by some variance between individual calibration facilities. However, it is unlikely that the lack of this data would have resulted in failed tests becoming passes.

The results show that a low-cost meter is (as might be expected) capable of providing a noise level indication, but also that a number of instruments that claim IEC61672 compliance are not compliant. If an instrument is required for accurate noise measurements it is recommended that any claims of compliance are confirmed. This can be established by asking for evidence of type approval, typically in the form of a certificate from a national metrology institute, and not by just relying on the marketing of the sound level meter.