by David Ingersoll
For many years, fabric-wrapped fiberglass panels have been a common solution for interior acoustic treatment. The composition of these panels includes a heavy density fiberglass board wrapped in a decorative, acoustically breathable fabric. The selected fabric can either compliment the design of a space, or can be matched to blend in and go unnoticed.
While woven polyester fabrics are most common, other facing material options include lightweight polyvinyl chloride (PVC) films, polyolefin, and polypropylene. Natural fibers, such as wool, silk, and cotton, are not typically used, as they are hydrographic and expand and contract due to water absorption. The fiberglass veil material used for paintable acoustic panels is designed to achieve a Class-A fire rating, as well as provide a porous, permeable facing suitable for coating.
Paintable panels offer designers the flexibility to blend in or stand out when adding acoustic treatment to a space. These panels can be used on walls or ceilings, and offer an alternative to the traditional fabric-wrapped types. Any RAL (Reichs-Ausschuß für Lieferbedingungen und Gütesicherung) hue can be selected and matched, thus allowing for a broad range of color choices for the boldest or the most modest design approach.
The uncoated facing provides a smooth, clean white surface when the color is desired. Painting of the facing material is typically done in the factory. Field painting is also acceptable, when the proper material is used and directions are correctly followed.
Noise reduction coefficient (NRC) is the measure of how much sound energy is absorbed, as opposed to reflected, by a particular object or piece of material. It is measured by testing per ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method. An analogy would be windows. A closed window would reflect 100 percent of the sound energy hitting it. This would represent an NRC of 0.00, or no energy being absorbed. An open window would absorb 100 percent of the energy, and this would represent an NRC of 1. While not technically accurate, this analogy gives an understanding of the measure of absorption.
Measuring reverberation time (RT) in a space is done by testing for RT60. This represents the time it takes a sound to decay by 60 dB. The more absorption in a space, the less time it takes for the sound to decay, or lower by 60 dB. A space with very little absorption will have a high RT60 time. A typical range for a reflective space can be anywhere from four to eight seconds. By measuring the RT60, building professionals can determine just how much sound absorption a space requires to be acoustically correct. Typical design times for RT60 range from half to two-and-a-half seconds. Facilities designed for music, such as smaller arenas, theaters, and houses of worship, are designed to be slightly reflective or lively, and are often between a RT60 time of one-and-a-half to two-and-a-half seconds. Larger spaces, such as gymnasiums, auditoriums, and sports halls, are usually designed to stay within RT60 times of one-and-a-half to two seconds. Smaller spaces where the acoustic goal is speech intelligibility (e.g. conference rooms and restaurants) will often have a RT60 goal of one to one-and-a-half seconds. Learning environments such as classrooms, libraries, and other educational spaces are usually designed to be well under a second for RT60 times.
Fabric-wrapped acoustical panels are offered in multiple thicknesses. Standard thicknesses are usually 13, 25, 38, and 50 mm (½, 1, 1 ½, and 2 in.) and custom sizes are up to 100 mm (4 in.). The thickness of the panel has a direct effect on the performance. Generally, a thicker panel will have a higher NRC value. It will also perform better at lower-end frequencies. In most cases, the highest overall NRC is desired, although in some specialty circumstances, tuned absorbers are preferred.
Flammability rating is an important aspect of materials hung on the walls and ceilings of public spaces. Wall and ceiling materials are tested for flammability rating per ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials. This is also known as the Steiner Tunnel Test. It tests for flame spread and smoke development. It is represented by two numbers. A Class-A material will have a flame spread number under 25, and a smoke developed number under 450.