NRC and CAC of acoustical ceilings in healthcare facilities
Ceilings are typically the only surfaces available for sound absorptive finishes for noise control in healthcare facilities. Regular acoustical ceiling panels, without film facing, are allowed in many healthcare spaces. The two important properties to keep in mind for acoustical ceiling panels are Noise Reduction Coefficient (NRC) and Ceiling Attenuation Class (CAC). NRC is a measure of the sound absorption of the panel, the percentage of sound energy not reflected by the panel, which ranges from 0 to 1.0. CAC is a measure of how well the panel blocks sound transmission; the CAC test actually measures how sound is blocked when traveling from one room, into the ceiling plenum with no wall above the ceiling and into another room with the same type of ceiling. CAC ranges from 0 up to 40-45 for ceiling panels. Even though CAC was developed for this double-pass arrangement, it has become a useful ranking metric for how well ceiling panels block noise transmission from the ceiling plenum.
Glass fiber ceiling panels have high NRC ratings (0.90 or greater) for sound absorption, but low CAC ratings for blocking ceiling plenum noise. These panels are very useful in two types of areas:
- where little or no mechanical system noise sources are in the ceiling plenum, or
- where higher background sound levels are acceptable and speech privacy and/or noise control is important (reception/admitting/waiting areas, cafeterias).
Mineral fiber ceiling panels have high CAC ratings (30 or greater) and are good for blocking noise from ceiling equipment noise, but they have a wide range of possible NRC performance that falls below the NRC performance of glass fiber panels. High-performance mineral fiber ceiling panels can achieve a NRC of 0.70 and a CAC of 30 or greater, and provide good sound absorption at speech frequencies, so they are useful in many areas of hospitals.