Ceiling attenuation class
Ceiling attenuation class (CAC) is the acoustical ceiling performance parameter most associated with speech privacy. It indicates the ability of a ceiling to block sound in one area from passing up into the plenum and transmitting back down into an adjacent area sharing the same plenum. CAC is an important consideration between adjacent closed spaces as well as between nearby closed and open areas.
It is measured according to ASTM E1414, Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum. The higher the CAC, the better the ceiling acts as a barrier to sound intrusion between the spaces and the better the sound isolation and speech privacy performance.
A ceiling with a CAC less than 25 is considered low performance, one with a CAC that is greater than 35, high performance. A CAC that is greater than 35 should be the minimum for closed plan spaces.
The right combination of NRC and CAC values represents the best approach to ceiling selection tailored to the needs of the space. To make selection easier, there are acoustical ceiling systems today offering both sound absorption and blocking in the same panel. By providing an ideal combination of a high CAC and a high NRC, these panels deliver the best solution for both keeping noise levels down and conversations private in either closed or open plan spaces.
When examining NRC and CAC values, base ceiling selection on Underwriters Laboratories (UL)-classified acoustical performance parameters. A UL label on a carton certifies the ceiling panels have been tested by an independent third party on a continuing basis to ensure the panels’ performance meets or exceeds published values.
Sound transmission class
Sound transmission class (STC) indicates the ability of a wall to block the transmission of sound through it into an adjacent space. The higher the number, the better the construction acts as a barrier to sound transmission. A wall system with an STC less than 35 is considered low performance, one with an STC greater than 45, high performance. It is measured according to ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions
and Elements.
Balanced acoustical design
Attaining speech privacy is dependent on good acoustical design and the proper selection of interior systems and materials. The proper choice of ceiling is vital because a ceiling’s ability to block sound can both affect the quality of sound within a space and limit the sound intrusion between spaces. It is a key element not only in creating an acoustical environment that can maintain speech privacy, but also in providing greater overall acoustic comfort and a reduction in noise-related annoyance.
One of the most effective and often least costly methods for achieving speech privacy is the balanced acoustical design approach. It consists of three components:
- absorb sound within a space with high performance acoustical ceilings that prevent sound from building up and intruding into an adjacent space;
- block sound transmission between spaces with a combination of high performance ceilings, effective wall and partition design, and proper lighting, HVAC, and door choices; and
- cover the space with an evenly distributed electronic sound masking system that can be tuned to meet the desired privacy level.
Speech privacy in closed spaces can be achieved, even at raised voice levels, using balanced acoustical design with attention to the right combination of acoustical values.
