Acoustical Transparency: A perforated panel must be acoustically transparent for noise to pass through it. Transparency is determined primarily by the percentage of open area in a panel. However, a panel with a single large hole will pass less sound than would a panel of equivalent open area but with many small perforations distributed across its face.

Ceilings are often considered to be boundaries that form a barrier across the top of a room. With perforated panels, however, another paradigm is available: Ceilings are also membranes that connect spaces and filter or modulate sound, light, and air. This makes perforated panels an important component in the acoustical designer's palette.

The following examples suggest how perforated ceilings can be used as pervious membranes:

1. Perforated metal allows varying degrees of physical separation without creating barriers to sound, light, and air. For example, a perforated ceiling in an atrium can provide visual screening and partial shade for the lower levels while permitting the free flow of sound, light, and air throughout the full height of the atrium.

Photo: Ceilings Plus Aluminum and wood can also be formed into lightweight beams, planks, and other rectangular sections that provide good acoustics and above ceiling access.

2. Reverberation time is directly linked to the volume of a space. Where a longer reverberation time is required, a perforated metal ceiling allows the space above the ceiling to be included in the room's volume. In the Schuster Performing Arts Center, for example, perforated panels allowed the space above the ceiling to contribute to the longer reverberation time required for orchestral performances.

Photo: Ceilings Plus Perforated panels at the Shuster Performing Arts Center, Dayton, OH, allowed space above the ceiling to increase the effective volume of the concert hall.

Alternatively, perforated panels can be used to decrease reverberation time by adding insulation to make a space more sound absorbing.

3. Perforated metal panels can be used as a visual screen for speakers and other audio equipment. This approach allows public address speakers and noise masking devices to be inconspicuously located above perforated metal ceilings to maintain a clean and uncluttered overhead appearance.