Civil Engineering Reference
In-Depth Information
Figure 8-2
Acoustic reflectance based on saddle shapes as blender and reflector of sound.
Sound transmission loss through the fabric is another important consideration in
public structures where building occupants must be shielded from outside noise. Like
sound reflectivity, transmission loss is highly dependant on frequency of vibration,
with tests on structural fabrics indicating a moderate transmission loss of
approximately 5 decibels at 100 Hertz, ranging up to 30 decibels at 500 Hertz.
(Normal human hearing is in the range from 20-15,000 Hz, with middle C having a
frequency of 262 Hz.).
Sound reflectivity can be decreased and transmission loss increased by installing
lightweight porous liner fabrics inside the space. Fiberglass insulation between two
layers of fabric can further increase transmission loss. With sufficient absorption,
neutral acoustic spaces can be achieved. A neutral acoustic balance is a space where
sounds generated inside are neither reflective nor absorbed. However the effects of
this inner fabric layer on day-lighting, fire safety and insulation must be considered,
as secondary layers also curtail the translucency of the fabric. Porous vertical banners
can also be suspended at intervals under the fabric roof in order to increase sound
absorption and break up the geometric reinforcement of the curved fabric roof.
8.5 Aesthetics
Tensioned fabric structures have a unique visual character founded on the following
features:
1. Fabric roof forms are curved between supporting elements in a manner
reflective of the flow of tension forces within the membrane. With the
exception of air-supported or air-inflated structures, these curvatures are
anticlastic in nature. The overwhelming majority of contemporary
construction is based on rectilinear forms, and the curving forms of fabric
structures give them an inherently different and dramatic character.
Search WWH ::
Custom Search