Low-frequency noise is a significant source of nuisance and has been the subject of extensive scientific research. Low-frequency noise generally refers to noise with frequencies below 100 Hz. People are generally less sensitive to these low frequencies because they have difficulty hearing them. The A-weighting is partly based on this and therefore often underestimates the presence of low-frequency noise.
However, when low-frequency noise is audible, it can relatively quickly lead to serious nuisance. Furthermore, there is considerable variation between individuals in sensitivity to low-frequency noise: both the frequencies that are audible and the sound levels at which nuisance is experienced vary considerably from person to person. This effect has been demonstrated in various (psychoacoustic) studies.
Low frequency curves
Various guidelines and assessment curves are used to assess low-frequency noise.
The differences between low-frequency assessment curves result from varying objectives, the percentiles used, and the extent to which nuisance perception and precautions are taken into account. A lower curve implies a higher level of protection for sensitive individuals.
The most important ones in the Netherlands are:
- Vercammen curve (3-10% experience discomfort when these noise levels are exceeded)
- The NSG guideline for low-frequency noise (hearing threshold at which 10% of older people perceive sound)
The LF curves apply to indoor measurements and should be measured in, for example, the bedroom. In many cases, we measure outdoors. For outdoor measurements, the LF curve can be estimated by including the attenuation of the average facade in the calculation.
The table below shows the indoor curves for the various standards and the indicative outdoor levels (if the source is external) that can be observed with a standard facade attenuation.
Comparison of limit values (dB, unweighted, whole numbers)
| ⅓ octave band (Hz) | Δvercammen | Δvercammen + Dfacade | Δlf-nsg | Δlf-nsg + Dfacade |
| 10 | 86 | 87 | - | - |
| 12.5 | 82 | 84 | - | - |
| 16 | 77 | 80 | - | - |
| 20 | 71 | 75 | 74 | 78 |
| 25 | 65 | 70 | 62 | 67 |
| 31.5 | 60 | 66 | 55 | 61 |
| 40 | 55 | 63 | 46 | 54 |
| 50 | 50 | 61 | 39 | 50 |
| 63 | 46 | 60 | 33 | 47 |
| 80 | 42 | 59 | 27 | 44 |
| 100 | 39 | - | 22 | 42 |
| 125 | 36 | - | - | - |
In the portal, the curves can be found under the "Low Frequency" category on the graphics page
Low frequencies:
- are less attenuated by walls
- are difficult to hear, but can be physically felt
- are more likely to cause annoyance, restlessness, and sleep problems
Standard dB(A) measurements underestimate this problem. Therefore, the Vercammen curve considers octave bands in the low frequency range.
Example of an indoor measurement over which the Vercammen curve has been plotted next to the LAeq,1mim levels
How does the curve work?
- Determine which curve should be used (for indoor or outdoor measurements)
- Use a sample rate of (at least) 1 minute for accurate results
- Determine the sound level for each of the curve's ⅓ octave bands (see table above).
- Compare each measured level with the curve chosen in step 1.
- Assess the exceedments
| Result | Meaning |
| Below the curve (< 0dB) | Generally acceptable |
| Around the curve (0 to +2 dB) | Nuisance possible |
| Above the curve (+3 to +5 dB) | Nuisance likely |
| Far above the curve (> +5dB) | Nuisance very likely |
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