Oltre il metallo -1- 20101112 p.1 - 42.cdr - DieMMe

Il problema del rumore - The noise problem
Attenuazione del rumore - Noise attenuation
Noise attenuation in the workplace
The reduction of noise in the
workplace has become an
essential requirement of modern
life, and has given rise to an
important series of theoretical
studies and experimental
research in the field of applied
acoustics. We should add that
technical progress certainly does
not help when it comes to noise
levels: on the contrary, in some
industrial processes, the increase
in noise is due to the very use of
new machinery. In an industrial
w o r k p l a c e , w e n e e d t o
distinguish between noise
deriving from machinery and the
room’s inherent noise.
a) the noise produced by
machinery depends mainly on
the vibrations of said machinery,
which can be carried in the loadbearing
structures of the
building and transformed into
acoustic vibrations. To reduce the
intensity of these vibrations, it is
essential we study the system
used to install the machine on
the building’s floor slab: the base
of the machinery must be well
insulated from the building’s
load-bearing structure, and
c o n n e c t i o n b e t w e e n t h e
machine and floor must be made
using efficient antivibration
mounts. In this way, the machine
tool, excited by the vibrations of
the individual mechanisms,
reacts in relation to its mass and
inertia, with low-frequency (nonacoustic)
vibrations, which
depend on its fixing systems. All
these problems must be
examined at the design stage
both of the machinery and the
building since any measures
taken once the building is
finished are inevitably more
expensive and less satisfactory. In
t h e c a s e o f i n d u s t r i a l
environments housing a number
of machines, each with a
different sound level, it is clearly
just the higher sound levels that
must be dealt with.
b) the room’s noise depends on
reverberation and on the various
s o u n d w a v e s r e f l e c t i o n
p h e n o m e n a . T o a v o i d
reverberation problems, the
room’s walls, floor and ceiling
must be covered with materials
featuring a high absorption
coefficient. Moreover, the
volume of the room must be
large enough to decrease sound
energy density. Interior surfaces
must be large to accommodate
extensive surfaces of absorbent
materials. Where possible, large
windows and openings should
be incorporated into the design,
preferably left open to allow
sound energy to escape outside.
The above-mentioned rules and
instructions for acoustic
conditioning should be borne in
mind when embarking on the
design of a new site for industrial
machining or processing.
However, the building is often
already completed, at which
point the only option is acoustic
correction to limit sound
intensity and the concentration
of reflected waves in some areas
of the space.
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