You probably already know that perforated metal sheet is often used as a facing for acoustical treatments, but if more people also realized that for many applications perforated metal is the best available facing material, there would be many more such applications.
Figure 13. Although it is not conspicuous, the ceiling of this classroom is made of perforated metal with glass fiber blanket in the space behind.
A great disadvantage of other commonly used sound absorptive treatments is that they cannot be cleaned or repainted without seriously degrading their sound absorptive properties. Perforated metals are unique as components of acoustically absorptive treatments because they can be cleaned or refinished without harming the absorptive properties for which they were designed, subject only to the proper choice of perforation size and spacing, described later.
Other important advantages of perforated metals in such applications are:
• inherent structural strength, compared with woven or felted facing materials; they can stand alone, if necessary;
• ability to be formed into complex curved shapes for architectural (visual) purposes;
• resistance to abuse and damage
• Finally, the chief architectural advantage of perforated metal is that it is basically uninteresting. It can be made to look like something else: for example, plain plaster.
Unfortunately, its neutral appearance creates difficulties for us when we try to illustrate this advantage in this booklet; photographs don't show up what is really going on!
