Noise Measuring

As our society increases its demands to minimize disruptive noise, so the requirement to measure and monitor noise increases as well. Over the years Nitro Consult has become greatly experienced in the problematics of noise associated with surface and underground construction sites, quarry operations and similar activities. Many of our commissions have also involved the measuring of traffic noise on roads and railways.

Different types of measurements depending on requirements
Noise can be measured in different ways; there is no absolute standard. The equivalent and maximal sound pressure levels can be measured over long periods of time with the aid of long-term recording instruments. Trigger levels, recording times etc can be remote-controlled easily and thereby adapted according to requirements. Moreover, when the trigger level is exceeded, short sound clips can be recorded for subsequent replay and frequency analysis. In especially tough conditions, such as when measuring the airblasts from tunnel and quarry blasting, Nitro Consult uses special microphones that are capable of withstanding such pressure shocks.

For smaller and more flexible measuring, we use handheld sound level meters. These small portable devices measure the sound pressure and can, if necessary, be adapted according to the characteristics of the room or area being measured. Everything from peak values to the equivalent sound level can be obtained from the measurements taken.

Noise and other undesirable sound
The Swedish Environmental Protection Agency (EPA) has drawn up environmental quality standards for authorities, which can also be used by private individuals and organizations. The EPA has also issued guidelines for the way in which measuring should be carried out, and also for how people can be protected. Most noise measurements are reported in decibels (dB), a logarithmic scale that is calculated relative to a chosen reference level such as 0.00002 Pa, the lowest sound pressure level the human ear can perceive. To enable the comfort level of noise to be determined, the results are often adapted according to the way in which we humans experience sound. This is called A-weighting, whose results are expressed in dB(A).

The human ear has a large working range: a frequency range of 20-20,000 Hz and a sound-pressure perception range of 0-130 dB. The pain threshold is 130 dB. By comparison, the sound pressure range of a normal conversation is 40-60 dB. An increase of 10 dB corresponds to a doubling of the sound pressure experienced by the human ear.

Reference projects
Nitro Consult is (and has been) carrying out extensive noise measuring in several infrastructure projects involving large-scale earthworks and rock excavation, with considerable noise being generated by activities such as drilling, blasting and piling. These projects include:

• The Stockholm City Line (Citybanan), a 6-km railway under the Swedish capital currently being constructed at a cost of SEK 16.8 billion (USD 2.4 billion)
• The Northern Link (Norra Länken), a 4-km mostly underground expressway currently under construction at a cost of a SEK 14 billion (USD 2 billion)
• The Southern Link (Södra Länken), a 6-km mostly underground expressway which opened to traffic in 2004 at a cost of SEK 7.9 billion (USD 1.13 billion). Both the Southern Link and Northern Link (above) are segments of the steadily materializing Stockholm Inner Orbital Expressway.