Noise measurement

Noise measurement or calculation of external noise from companies will most often appear as a definite requirement in connection with, for example, an environmental approval. We work with laboratories approved by the Danish Environmental Protection Agency to carry out noise measurements and calculations such as "Environmental noise - External noise".

In planning, you often need to know something about the future noise in connection with building and construction works. This may be the case, for example, if a new road is to be built, a noise screen is erected or housing is built near a road. In many cases, noise is investigated using calculations, and there can be many good reasons for this. One of the reasons why people often calculate rather than measure is i.a. that there is always some uncertainty associated with measurements, where more precise decision bases may sometimes be needed.

The uncertainty can i.a. due to:

• Background noise from other sources both from the external environment and internally
• The different operating scenarios
• The sound propagation conditions, which can both be due to terrain and meteorological conditions

Measurement methods

In order for a measurement to be approved as certified or accredited, it must be carried out as "Environmental measurement - External noise". This measurement can either be taken as a measurement in the gap (gap measurement) or as a source strength measurement (near field measurement). With both measurement methods, the company's noise load is determined at a point, which is often near the nearest neighbours.

External noise from companies, such as construction sites, is very relevant in big cities, where many of the constructions take place very close to apartment buildings. Here, constructions such as Metro, light rail, etc. can be mentioned in particular.

Gap measurement:

When a "difference measurement" is carried out, the measuring equipment is set up at a pre-defined point where you want to measure the noise. This will most often be at the border with neighboring residences. In some cases it will not be possible to measure due to excessive levels of background noise, long distances and low noise limits. For the same reason, the measurements are most often taken in the evening and nighttime, as it would be possible to measure here without large amounts of background noise from traffic etc. In certain cases, it is not possible to measure due to e.g. background noise, long distances and low noise limits.

With a milestone measurement, the noise contribution is measured under the exact operating situation that the company had during the measurement. A boundary measurement does not provide precise information about which noise sources are the reason why the limit has not been met. Here you get an overall overview of whether the level is within or exceeded. In some cases, a company will be able to stop plants, and through this, with the help of the exclusion method, you can find out which plants are particularly noisy and which will possibly require noise reduction measures to be taken.

Separation measurement provides, due to, among other things, distances to the noise source, high requirements for weather conditions during the measurement, including wind direction, wind strength, cloud cover, etc., and situations may therefore arise where more than one visit to the company is required.

Near-field measurement - Source strength measurement:

When measuring source strength, the measurement is made very close to the individual noise sources. Eg. can a noise contribution be measured at a distance of 1 meter from the noise source itself. The noise is recorded and then analysed, this is also where it is assessed whether contributions must be added for tones and/or impulses.

Once the noise contribution has been measured and analysed, it is converted into a source strength, which can be used to create an overview of the company's and the source's noise contribution at various points in the company's surroundings. When all the noise sources have been measured and calculated in the selected point, the noise contributions can be added together and the total noise contribution in the selected point is found. If a noise source is to be attenuated, the overall result of attenuation can already be calculated for the actual attenuation of the noise.

In contrast to the separation measurement, there are no great demands on the time and the meteorological conditions in order to be able to measure according to the source strength method.