Do you need to measure sound?

Choosing a model to suit your intended application is much more difficult that it appears.
NOTE: Price should be the last thing you look at, especially when it comes to someone's hearing!
Whilst an iPhone App may be appealing, convienent and cheap, it can often read out by a country mile!

Many factors need to be taken into consideration when investigating the purchase of a sound level meter.

The following covers many key topics and features involving the purchase of sound measuring device.
It is designed to give you an insight into sound level meters and uses.


1. NZ Standards for Sound/Noise

For Sound Level Meters, this is usually one of the major reasons why a unit is being purchased.
The first thing to know is almost all the measurements required by the standards are time-averaged, percentile or time exposed values.
The instantaneous dBA measurement which so many low cost products read out on their display's will generally NOT help you establish your correct sound parameters.

Either a company is required to measure the sound level at/within their location or consumers themselves are wanting to measure the level of the sound from a noise source or disturbance.
New Zealand as country is very much a "re-active" as opposed to a "pro-active" market when it comes to measuring sound.
Many industries are pro active in providing suitable hearing protection to workers and, to their best abilities, follow district planning for construction and commercial operation to provide a quiet-as-possible work environment.
They do however often fail to either measure/establish high sound levels or perform noise risk surveys.

There are several standards, bylaws, regulations and zonings that councils, district plannners, OSH and other regulatory bodies ashere to.
Most relate back to the AS/NZS standards.
The following are key examples currently in use in New Zealand:

• NZS 1269.1:2005 Occupational noise management
Measurement and assessment of noise immission and exposure

• NZS NZS 6801:2008 Acoustics
Measurement of environmental sound

• NZS NZS 6802:2008 Acoustics
Environmental noise

• NZS NZS 6803:1999 Acoustics
Construction noise

Each of these standards establish the sound level requirements of an industry/business as per the outline of the standard.
They will also advise the parameters of measurements that so often confuse a new comer to sound level measurement. (e.g. L10, L90, LAEQT, LAFMAX etc)

Before you invest in a sound measurement device, it is wise to either view the standard/s applicable to your intended use (available from http://shop.standards.co.nz/) or consult an acoustic technician or company.

This will aid you in purchasing the correct sound level meter with the correct features, specifications and measurement parameters required.


2. How do Sound Level Meters work

Put simply, a Sound Level Meter is (generally) a hand held device designed to measure a frequency and time-weighted value of the sound pressure level. It consists of a microphone, amplifier and usually an LCD display which indicates the measurement.
Typical measurements range from 30dBA (very quiet) to 140dBA (jet airplane taking off at close proximity)

3. Sound Level measurement parameters

Often the hardest one for new comers to understand.
Sources of noise are more often than not variable and impulsive. For example. A truck generally does not drive past the same location, at the same time each day, travelling at the exact same speed, using the same gear ratio, carrying the same load, with the same wind direction...... their are always variables.
Because sources of noise are variable, many of the standards used to measure their effect are based on "average" noise levels, over time.

Example. The common values throughout New Zealand for sound levels, in a residental zone, during the evening/overnight (e.g. 2200 -0700) weekdays are 45LAeq(t) and 75LAmax.

So what do these parameters mean and why doesn't my iPhone app measure them?

Firstly, most environmental sound levels are measured using the A weighted scale, as it relates to the nosie repsonse of the human ear.

LEQ, LEQ,T, LAeq(t) is referred to as the eqivalent continuous time averaged sound level. It is usually measured in dBA.
Why use Leq? It is the preferred method to describe sound levels that vary over time, which will result in a value which takes into account the total sound energy over the period of time measured.

Lmax, LAmax, LAFmax is referred to as the maximum noise level. It indicates the highest measured value during the measured time period.

Other measurement parameters such as L10, L90, dose, TWA are very common so knowing what parameters a sound level meter can measure, record and display will be paramount to your application.

Below are an example of some of the measurement parameters that the Pulsar Meters are capable of measuring, all available from Accurate Instruments.

Pulsar Model 14 - LA, LAmax, LC, LCmax
Pulsar Assessor - LA, LAeq(t), LCpeak, LEX
Pulsar Quantifier - LA, LAeq(t), LAmax, LCpeak, LAE, L10, L90 etc
Pulsar Nova- LA, LAeq(t), LAmax, LCpeak, LAE, L10, L90 etc, TWA, Dose
Pulsar doseBadge - LAVG, TWA, Dose, Pa2h


4. Class1 or Class2

Previously referred to as Type1 or Type2. International standards define the criteria that a sound level meter is require to meet. e.g. IEC 61672-1:2002.
Basically put Class1 meters are more accurate. At a reference frequency of 1kHz, the tolerance for Class 1 is +/- 1.9dB and for Class 2 the tolerance is +/- 2.2dB.
Basically, at the limits of the frequency range, a Class1 meter must have a better response and meet tighter tolerances.

So which Class do you need?
Usually, the application will lay out the Class/Type required. If it doesn't, Class2 is suitable.
NOTE: Very low cost meters and smart phone apps very rarely meet any Class.

5. Calibration

Why is calibration so important?
Sound Level Meters measure very small changes in pressure. The most sensitive part of the meter is the microphone.
Every day use, knocks and use in varying environmental conditions can lead to possible variations. Regular calibration gives the assurance that the meter is still accurate and measuring correctly.
Calibration testing often also results in pro-longing the live of the instrument.

More importantly, traceable calibration of the meter, especially a unit supplied with certification, is critical in legal purposes, occupational noise and hearing protection, environmental, planning, boundary monitoring etc.

Measurement kits including acoustic calibrators, which also are supplied with calibration certificates are also used prior and after a noise survey has been performed.
So meters will even keep an internal record of not only the factory testing status but also the frequent site use of a calibrator.


6. Warranty, backup and support

Trying to buy a meter online from a company that advertises but doesn't stock sound level meters?
Trying to save a little bit of money buying from overseas? Found a cheap parallel import on Trade Me?
You may come well and truly "unstuck" quite quickly.

Often sound level meter kits and packages vary in different countries around the world. Power cables, batteries, reference manuals, software etc can all vary in different locations.
In some cases, certain model and specification meters can only be sold in some markets.

Who will back you up? Who will answer your questions? Who will train you?
Warranty?

Accurate Instruments has an established sound level network for sales, support/backup, warranty and loan/hire equipment. We have various models of meters in stock for sale and can arrange product training seminars on the equipment.


7. Brand & Price

Price is usually the determining factor that will influence people's buying habit/s.
Usually people will have in mind a price before really knowing what sound product they need.
Buying on price or brand alone will often get you either an under specified or possibly an over specified meter.

Once you have established what you actually are required to measure, the required Class and measurement parameters of the meter as well as the general features and specifications, then it is all about matching a price and brand to this.
A quality Sound Level Meter is an investment.



Other features/specifications that can also be assessed in the purchase phase of a meter include data logging, reporting options, octave band measurement, real time analysers etc.

A glossary of common terms can be viewed by clicking here