The innovative nature of the Harmonica index

The development and approval of a noise index intended for the general public was at the heart of the European Life Environment programme's Harmonica project, which took place between the end of 2011 and the end of 2014. This new index is particularly innovative for three reasons:

It is innovative in terms of its technical design, as it takes both the background noise and noise peaks into account

The usual indicators essentially take into account the average intensity of noise (with noise energy indicators), but do not indicate whether the nature of noise is mainly continuous or sporadic (that is to say with noise peaks that are added to the area's background noise, caused for example by aircraft, trains, particularly noisy motor vehicles).

The aim of the Harmonica project was, therefore, to develop an adimensional index that would take into account the two main components that influence the noise environment, namely the background nose, and the characteristics of noise peaks that stand out from this background noise.

It is innovative in terms of how it was developed: public participation

Until now, in the field of environmental noise, indicators tended to be designed between specialists. The Harmonica project involved the population in the design of this index. Face to face "in situ" interviews and laboratory tests allowed us to evaluate the comprehensibility, the acceptability, and the relevance of various suggested parameters, with respect to their capacity to accurately reflect the quality of the acoustic environment perceived and to take into account the public's perception when developing the new index.

It is innovative in terms of its form: an easy-to-understand graphical representation

Noise is often represented in terms of its pressure, by using the physical unit of acoustic pressure: the decibel (dB). With this unit, variations in noise are calculated using a logarithmic scale. This means that a doubling in the noise energy level results in an increase of 3 dB. If two vehicles passing by both produce 60 dB each, the result would not be an arithmetic addition of the levels (i.e. 60+60=120), but rather 63 dB. The complexity of the decibel makes it difficult for the general public and authorities to take ownership of the issue of environmental noise.

This is why the Harmonica index was developed with a scale of 0 to 10 - without using the decibel - in order to make it easy for anyone to understand.

In order to reflect variations in noise throughout the day, it was decided to develop an hourly index, allowing a clear representation of the variation of noise levels throughout the day, taking both background noise and noise peaks into account. Average indices for daytime periods (6 am - 10 pm) and night periods (10 pm to 6 am) and for the entire day (24h) are also calculated.