Applications - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 284

Motilla de Palancar in Spain when the A-3 motorway Madrid-Valencia was finished
in 1999 and all the traffic load was removed from the center of the city. The
displacement of traffic resulted a reduction of noise from 3 to 7.5 dB(A) with an
average noise in the city of 60 dB(A) as recommended by the World Health
Organization. This change has also produced a more satisfactory quality of
human life, as seen from investigation of 100 people who had their homes in
front of the principal road.
The noise of traffic is increasing in cities, with reduction of the extension of quiet
areas, and this phenomenon is a continuous font of public concern for the annoy-
ance produced and for the reduction of communication capacity of a densely
aggregated people. The policy of removing traffic noise from the cities has exposed
the outskirts to an increasing level of noise. In Europe 20 % of population is
exposed to excessive road traffic noise, and this represents a severe health risk. In
this issue the physical measurement of urban noise is not enough to allow architects,
town planners, and landscape designers to initiate an action to revaluate and
improving the sonic environment, in other words to create the changed sound in
the right space,

including in this process the subjective sonic experience of

dwellers.
A way to escape or in part to solve this problem is to create green areas, urban
parks far from the traffic congestion, but often in urban areas and specifically in
urban parks reduction of traffic noise is not easily made.
A further possibility consists in masking the traffic noise, when it is at a lowest
level, with wanted sounds such as water fountains or playback of bird songs.
Waterfalls can represent a distracting sound that could help to alleviate the sonic
annoyance. An experiment is described by De Coensel et al. ( 2011 ) asking
100 volunteers (45 women, 55 men) to evaluate in the laboratory the effect of
waterfalls and bird song to mask road traffic by binaural acoustic files. The addition
of fountain sound reduced the loudness of the traffic noise only when the traffic
noise had a low temporal variability, less pulsing, but the addition of the sound of
singing birds significantly enhanced soundscape pleasantness and eventfulness,
more than the addition of water sounds.
This experiment clearly demonstrates that the loudness of unwanted sounds
should not be the only direction in acoustic design but that the soundscape quality
is strongly influenced by the meaning associated with the different sounds.
Jeon et al. ( 2010 ) have demonstrated that the water sounds such as “stream” and
“waves of lakes” sounds can efficiently mask urban noise, when the level of the
water sounds are similar or not less 3 dB below the level of the urban noise. This
strategy seems an efficient method to reshape and improve outdoor urban spaces.
The manipulation of sound sources allows modifying the sonic environment. In
this way the displacement of two annoying sounds does not change total annoyance,
but is possible to overlap an annoying sound with a sound source of preferred sound
quality and to create a masking effect.
Noise attenuation can be obtained by engineering barriers or by natural ones. In
this second case the utilization of plants is very common because plants can
produce many contemporary benefits such as soil cover, habitat for animals,
atmospheric pollutant absorption, scenic view, and finally a sound barrier. In a