Trees and shrubs have been used for many years
to reduce traffic noise from busy roads. Research
now shows that plants can also help to reduce
background noise levels in buildings. Some plant
species are more effective than others and the
benefits are more pronounced in buildings with
hard, reflective surfaces.
Research
Tests carried out by Rentokil Initial Research
and Development suggested that interior plants
can absorb or reflect background noise in buildings,
thereby making the environment more comfortable
for the occupants. The effect appears to be dependent
on plant type, planting density, location and
sound frequency. To investigate the potential
acoustic benefits of interior plants in more detail,
further research was carried out by a post graduate
student, Peter Costa, at South Bank University,
London. Rentokil supported this work by providing
access to computer data banks, technical advice,
plant specimens and test sites.
To
quantify the acoustic effect, the sound absorption
coefficients of a number of plant species were measured
and compared with other building materials. The
higher the absorption coefficient, the better the
material is at absorbing sound - a coefficient of
0.25 means that a quarter of the sound is absorbed,
0.50 half the sound and so on.
Table
of absorbing coefficients (costa 1992)
The
study indicates that plants are generally more efficient
at absorbing high sound frequencies than low sound frequencies.
Good examples of this are Spathiphyllum Wallisii (Peace
Lily), Philodendron Scandens (Sweetheart Plant), Dracaena
Marginata (Madagascan Dragon Tree) and Ficus Benjamina
(weeping Fig). High frequencies cause the most irritation
to building occupants so the benefit of having plants
becomes clear.
Use
in Building
The
noise reducing benefits of plants will be most pronounced
in acoustically "live" buildings, i.e. those
with hard reflective surfaces such as marble floors,
plaster walls and large expanses of glass. Plants will
have very little effect in acoustically "dead"
areas, such as rooms with thick carpets, curtains and
panelled walls. In addition:
•
Big
planters have more effect than small planters
•
Bigger
planters have more mulch and more plants. It follows
that they make a larger impact on room acoustics.
•
Several
arrangements are better than a concentrated location.
•
Positioning
several arrangements around a room would work better
than concentrating the planting in one location.
This way the surface area of the plants exposed
to the noise may be maximized.
•
Arrangements
comprising different plants in groups of three or
five appear to work better than individual plants.
•
Near
the edges and corners would be better than in the
centre of a room. In these positions sound reflected
from walls may be intercepted more easily by the
plants.
