Our sound rated acoustical division has pioneered major technological advances in the field of sound attenuation. Whether designing a sound stage, performing arts center, broadcast facility, school band/rehearsal room or a home theater, let the SA team assist you from product design, selection, through completion.
Sound is defined as pressure variations (oscillations) in air, water, or other mediums that can be detected by the human ear and the number of vibrations per second is referred to as the frequency of sound and is measured in Hertz or Hz. Human hearing ranges from approximately 20 Hz to 20,000 Hz, with the frequencies of speech ranging from 20 Hz to 8,000 Hz. Sound level meters are designed with a series of filters over the audible frequency range to simulate the varying sensitivity of the human ear. This is referred to as A-Weighting and measured sound power levels are designated as dBA.
The term STC stands for Sound Transmission Classification and is a numerical rating system derived from measured values of sound transmission loss based on testing criteria outlined in ASTM E90 and ASTM E413. This provides the Industry accepted method of determining sound reduction effectiveness. Testing should be performed by a laboratory accredited by NIST (National Institute of Standards and Technology) under the NVLAP (National Voluntary Laboratory Accreditation Program) in order to assure the effectiveness of the manufacturer’s assembly. Test results issued by the laboratory are identified as Sound Transmission Lost Tests and are assigned a dated report number associated with the manufacturer. This report, signed by the technician, will generally contain a description of the tested assembly, the test method utilized and transmission loss (TL) results in the sixteen transmission loss readings between 125 and 4000 Hertz (Hz) 1/3 octave bands plotted against the standard curve established in ASTM E413. This calculation establishes the single numbered sound transmission rating.
It should be noted that laboratory testing is done under ideal conditions. Many uncontrollable conditions affect the field installed assembly versus the laboratory tested assembly which could reduce the effectiveness by as much as 5 decibels (dB) or more. The higher rated assemblies can compensate somewhat for this so the designer should specify an assembly rated at 5 decibels higher than the actual field rating requirement.
Vision lites can reduce the overall effectiveness of acoustic doors but are often necessary for many reasons. Glass is rigid and therefore does not exhibit very acceptable sound reduction properties. However, the use of double paned laminated glass of different thicknesses tends to increase the effectiveness and the combination of each pane vibrating at different frequencies coupled with gasketed isolation and airspace between works quite well.
It is imperative that acoustic door assemblies are installed with precision. Noise, like water, seeks the point of least resistance and therefore frames must be installed plumb, square and true, doors must be adjusted for proper clearance, thresholds must be level and all perimeter seals, door bottoms and astragals must be properly adjusted. Please refer to the acoustics installation instructions for detailed information about this.