ADVANCED EQUIPMENT CORPORATION offers operable walls in a wide range of panel constructions. Each type of panel has been sound tested for STC value by a licensed acoustical engineer in an independent acoustical laboratory. AEC has established minimum NIC values which one can expect to achieve for each type of panel should the operable walls be field sound tested and providing that the surrounding building construction is compatible with the specified rating. The STC, NIC and NRC values (where appropriate) can be found on the PANEL FEATURES CHART below.
NIC - NOISE ISOLATION CLASS
A single number rating derived from a standardized ASTM field acoustical test procedure. The test is based on measurement of sound pressure lever differences on each side of the field installed product, adjusted to compensate for ambient noise levels. No adjustment of the value is made to compensate for sound absorption in the "receiving room". Thus, the result is comparable to that perceived by the human ear. A NIC rating of 40 is considered very good for an operable wall. As with STC, the higher the rating the better the operable wall is at stopping sound transmission.
Acoustical Engineers consider NIC measurement the most utilitarian and widely used method of determining the sound reducing effectiveness of operable walls. The NIC value, being determined by field testing the actual product purchased for use by the Owner/Operator, usually predicts Customer Satisfaction. A further advantage of field measurement of NIC is the ability to locate, define and correct sound leakage not related to the operable wall. Examples would be holes in sound barrier above ceiling, or common ductwork or conduit.
AEC considers field measurement of NIC, either optional or mandatory testing, to be the way to determine and control acoustical effectiveness of operable walls. It is recommended that one should not rely on STC to predict Customer Satisfaction.
STC – SOUND TRANSMISSION CLASS
A single number rating derived from a standardized ASTM acoustical laboratory test procedure. Testing is conducted on a small 14’x 9’ operable wall specimen in a controlled laboratory environment. The rating provides an estimate of the acoustical performance and may be used to rank or compare the sound reducing effectiveness of operable walls. Typical values for operable walls range from 38 to 54. The lower the number the less effective the wall will be in stopping sound transmission to the adjacent space.
Advanced Equipment Corporation does not consider laboratory tests, alone, a reliable predictor of acoustical effectiveness that may be necessary for Customer or Client satisfaction. The internal construction of the operable wall test specimen and clearance and dimensions of acoustical seals are not necessarily defined. Therefore, it may not be possible for an observer to know if the product installed in the field is representative of the specimen tested. Since the installed operable wall may not be comparable to the test specimen and sound leaks produced by installation of the actual product in the field may compromise acoustical effectiveness, STC is often not considered a suitable specification criterion. STC may prove to be unrelated to in-place results achieved by the production operable wall.
NRC – NOISE REDUCTION COEFFICIENT
A single figure rating derived from a standardized ASTM Acoustical Laboratory test procedure. Differences between the reverberation time within the laboratory, with and without a specimen of known area, and at various frequencies are used to calculate this measure of a percentage of reduction of sound energy due to frictional loss within the absorptive medium. Having an established value of noise reduction contributed by a known area and location of operable wall surface assists the Acoustical Consultant to evaluate, predict and adjust various acoustical properties of the space under study.
Operable Wall surfaces can be made to provide a significant NRC by several means. Perforated steel panel surfaces with highly absorptive medium within the panel; fibrous board substrate, similar to ceiling tile; dense, semi-rigid glass fiber bat substrate. It is best to consult with AEC’s home office to discuss suitable combinations of substrate and finish material, and to consider relative resistance to impact damage that may be encountered by some absorptive materials when placed in location s where impact can occur.
When designing operable walls which are to provide significant noise reduction, one needs to be aware that the finish material which may used to cover the absorptive surface must be "acoustically transparent". For example, covering an absorptive surface with solid material such as vinyl wall covering will change that surface to Non-Absorptive. On the other hand, using an unbacked woven fabric, or many constructions of wall carpet will provide the necessary protective/decorative surface without significantly negating the noise reduction properties.
Advanced Equipment suggests the Architect, Designer, or Owner employ the services of a qualified Acoustical Consultant to assist in design and help assure overall Customer Satisfaction. Proper design and control of acoustical properties frequently avoids unpleasant and costly surprises, and at the same time, enhances the functionality of the facility.
One way to learn the location of Acoustical Consultants in your area is to contact the National Council of Acoustical Consultants – NCAC – in Springfield, N.J. NCAC does not endorse AEC products.