Absorption:

In acoustics, the energy of sound waves being taken in (entering) the surface of any material rather than being bounced off or reflected. Materials are rated in terms of their ability to absorb sounds.

Acoustical Materials: 

Materials which have high absorption coefficients.

Amplitude:

The maximum variation of any wave from its mean value. Increasing a sound wave's amplitude increases its loudness.

Articulation Class (AC):

Rates the listener's ability to understand the spoken word within a space, expressed as a decimal with 1.0 being perfectly understandable. The Privacy-Index is derived from the AI calculation. Lower AI ratings (less than 2.0) indicate that adjacent spoken works are less intelligible, therefore less distracting. The sum of the weighted sound attenuations in a series of 15 test bands. Note: AC has replaced Noise Isolation Class (NIC) as the accepted industry standard performance value. NIC is based on hearing sensitivity rather than discernment of actual speech, which is the primary concern in open office layouts prevalent in acoustical design work. Verify the rating methodology with manufacturer's published data.

Articulation index (AI):

Measure of speech intelligibility in a room. A numerical value ranging from 0 to 1. In an open-plan office, an AI of 0.1 is low, indicating that little, is any, of a conversation will be intelligible on the other side of the screen. An AI of 0.6 would make for poor speech privacy.

Attenuation:

In acoustics, the diluting or holding back of the energy of sound waves as they pass through a material. Materials are rated for their ability to prevent sounds from traveling through them.

Ceiling Attenuation Class (CAC):

Rates a ceiling's efficiency as a barrier to airborne sound transmission between adjacent closed offices. Shown as a minimum value, previously expressed as CSTC (Ceiling Sound Transmission Class). A single-figure rating derived from the normalized ceiling attenuation values in accordance with classification ASTM E 413, except that the resultant rating shall be designated ceiling attenuation class. (Defined in ASTM E 1414.) An acoustical unit with a high CAC may have a low NRC.

Ceiling Sound Transmission:

In a suspended ceiling construction, the transmission of sound between adjoining rooms by way of the path consisting of the ceiling of each room and the continuous plenum over, and common to, both rooms.

dBA (A-weighted decibel):

A single-number measurement based on the decibel but weighted to approximate the response of the human ear with respect to frequencies.

Decibel (dB):

A unit to express differences in power. In acoustics, equal to ten times the logarithm of the ratio of one sound and a lower-intensity reference sound. One decibel indicates a difference of about 26% and is about the smallest change the ear can detect. The dB level is a logarithm quantity; the maximum normal level is approximately 120dB.

Flanking Sound Path:

A sound transmission path, such as a structural path, that bypasses a transmission barrier.

Flanking Sound Path:

Cycles per unit of time. Usually expressed in Hertz (Hz). The frequencies of audible speech lie in the range of 400-2000 Hz.

Hertz (Hz):

One cycle per second.

Noise Isolation Class Prime (NIC¹):

A single-number rating of the acoustical performance of any screen-ceiling combination. It is a measure of speech privacy, with higher numbers indicating greater privacy. Determined by plotting the functional interzone attenuation of the screen-ceiling combination against frequency.

Noise Isolation Class (NIC):

A single-number rating of the sound-isolating performance of a building element. Used in place of when flanking sound paths cannot be isolated to establish the Field Sound Transmission Class (FSTC).

Open Plan Office: 

An office in which acoustical screens, most commonly 60-inches high, are used in place of ceiling-high partitions. Ceilings used in open plan offices must have different acoustical properties than those used in closed offices.

pin Perforation:

A method of improving the acoustical performance of a ceiling tile or panel by punching holes in its surface during manufacture.

plenum Barrier:

Vertical surface framed from the structure above to the finished ceiling and sealed to prevent the passage of air or sound.

reverberation: 

Persistence of reflected sound in a room after its source has stopped emitting sound.

reverberation TIME:

Time required for a sound to decay to a value one millionth of its original intensity or to drop 60 decibels.

Sound ATTENUATION: 

The reduction in the intensity or in the sound pressure level of sound which is transmitted from one point to another.

Sound LEAKS: 

Cracks under doors, openings in a wall, pipe or wiring holes, etc., which allow sound to escape through a structure from one room to another.

Sound Transmission class (STC): 

A single-number rating of a structure's efficiency as a barrier to airborne sound at 16 speech frequencies from 125 to 4000 Hz. (See ASTM procedure E 1414 for rating method.) Rates the ability of a wall or others construction to block sound; STC is a decibel measure of the difference between the sound energy striking the panel or construction on one side and the sound energy transmitted from the other side. This includes sound from all angles of direction, and from low and high sounds frequencies.

Sound TRANSMISSION LOSS:

The amount of sound lost as the sound travels through a material. Acoustical ceiling assemblies are rated in terms of Sound Transmission Classifications. An STC value of 20-25 would indicate that even low speech would be audible in an adjoining room. An STC value of 50-60, on the other hand, would indicate that loud sound would be heard only faintly or not at all.