Confidential
‘Confidential’ represents a PI rating of 95 to 100 percent. Conversations within a space may be partially heard, but definitely not understood beyond the confines of the space. Any nearby occupants may hear muffled sounds but spoken words are not intelligible.
Non-intrusive
Representing a PI rating between 80 and 95 percent, in ‘non-intrusive’ (or ‘normal’), conversations can be partially overheard, and some words or phrases may be intelligible. Nearby occupants may hear some of the conversation, but the loudness of speech is not distracting, and they can generally continue what they are doing.
Non-intrusive speech privacy is a common goal for open-plan environments, especially where ‘knowledge worker’ productivity is a key issue. However, it is generally not adequate in functional environments with closed plans such as medical facilities, law firms, financial service organizations, or human resource departments, where confidential privacy levels are generally required.
Marginal
‘Marginal’ (or ‘poor’) means a PI rating of 60 to 80 percent. Most conversations can be overheard and are likely intelligible. Nearby occupants can understand most words and sentences, and the loudness of speech can be distracting to them.
No privacy
At a PI rating of 60 percent or less, virtually all conversations can be clearly overheard and are fully intelligible. Nearby occupants can typically understand all words and sentences, and the loudness of speech can be a constant distraction.
Open- or closed-plan spaces
Improving the acoustic environment in commercial office spaces to meet LEED criteria regarding reverberation time and, in turn, both speech intelligibility and speech privacy, is not difficult as long as attention is paid to matching the performance features of the ceiling to the needs of the space. One of the best solutions for keeping noise levels down and conversations private in open- or closed-plan spaces is the use of a high-performance acoustical ceiling that combines the right mix of sound absorption as denoted by its noise reduction coefficient (NRC) and sound blocking as denoted by its ceiling attenuation class (CAC).
The NRC indicates the ability of a ceiling to absorb sound from all angles. It is expressed as a number between 0.00 and 1.00, and indicates the average percentage of sound that it absorbs. An NRC of 0.60 means a ceiling absorbs 60 percent of the sound striking it. The higher the number, the better the ceiling acts as a sound-absorber. A ceiling with an NRC less than 0.50 is considered low performance, one with an NRC greater than 0.70 as high performance. It is measured according to ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.
The CAC indicates the ability of a ceiling to block sound in one space from passing up into the plenum and transmitting back down into an adjacent space that shares the same plenum. The higher the number, the better the ceiling will act as a barrier to sound intrusion between the spaces. A ceiling with a CAC of 25 or less is considered low-performance, one with a CAC of 35 or greater as high-performance. It is measured according to ASTM E1414, Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum.
CAC is the acoustical ceiling rating most often associated with speech privacy. As a result, it is an important consideration between adjacent closed spaces as well as between adjacent closed and open spaces, and in open spaces where collaboration or teaming areas are located.
Ceiling selection
The right combination of NRC and CAC represents the best approach to ceiling selection tailored to the needs of a space. In closed-plan spaces, speech privacy between adjacent spaces and speech intelligibility within the space itself is essential. As a result, one should select ceilings combining
a high CAC of 35 to 40 to block sound from traveling into adjoining spaces, and a moderate to high NRC to decrease unwanted sound within the space. An NRC of 0.60 to 0.70 is generally adequate for smaller spaces, while an NRC of 0.75 to 0.85 is preferred for larger ones.
In open-plan spaces where both focus areas and collaboration areas are located, one should specify ceilings that combine a moderate to high NRC (0.65 to 0.90) to decrease reverberant sound, and a moderate to high CAC (30 to 40) to block sound from traveling into adjoining spaces. Selection will depend on the degree of ceiling coverage above the space.
When comparing NRC and CAC ratings, it is best to make ceiling selection based 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.
