Noise Reduction Coefficient
Encyclopedia
The noise reduction coefficient (commonly abbreviated NRC) is a scalar
representation of the amount of sound
energy
absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection
; an NRC of 1 indicates perfect absorption
.
Building materials, especially interior finishes, through standard testing earn ratings of STC (Sound Transmission Class
) and NRC based on their sound characteristics. NRC generally applies to a single material such as on the surface of a wall which determines the reverb or liveliness of a room. STC generally applies to the assembly that composes the wall, including framing, insulation, sheet products (gypsum wallboard for example) and a surface material (such as vinyl wallcovering) which limits the amount of sound that travels through the wall assembly into an adjacent space.
NRC (Noise Reduction Coefficient) is an arithmetic value average of sound absorption coefficients at frequencies of 250, 500, 1000 and 2000 Hz indicating a material's ability to absorb sound.
In particular, it is the average
of four sound absorption coefficients of the particular surface at frequencies of 125, 250 Hz
, 500 Hz, 1000 Hz, 2000, and 4000 Hz. These frequencies encompass the fundamental frequencies and first few overtones of typical human speech, and, therefore, the NRC provides a decent and simple quantification of how well the particular surface will absorb the human voice
. A more broad frequency range should be considered for applications such as music or controlling mechanical noise.
Specifications for materials used in sound absorption commonly include an NRC for simplicity, in addition to more detailed frequency
vs amplitude
charts.
Scalar (mathematics)
In linear algebra, real numbers are called scalars and relate to vectors in a vector space through the operation of scalar multiplication, in which a vector can be multiplied by a number to produce another vector....
representation of the amount of sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
; an NRC of 1 indicates perfect absorption
Absorption (acoustics)
Acoustic absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts. Acoustic absorption is represented by the symbol A in calculations...
.
Building materials, especially interior finishes, through standard testing earn ratings of STC (Sound Transmission Class
Sound transmission class
Sound Transmission Class is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations . Outside the USA, the Sound Reduction Index ISO standard is used...
) and NRC based on their sound characteristics. NRC generally applies to a single material such as on the surface of a wall which determines the reverb or liveliness of a room. STC generally applies to the assembly that composes the wall, including framing, insulation, sheet products (gypsum wallboard for example) and a surface material (such as vinyl wallcovering) which limits the amount of sound that travels through the wall assembly into an adjacent space.
NRC (Noise Reduction Coefficient) is an arithmetic value average of sound absorption coefficients at frequencies of 250, 500, 1000 and 2000 Hz indicating a material's ability to absorb sound.
In particular, it is the average
Average
In mathematics, an average, or central tendency of a data set is a measure of the "middle" value of the data set. Average is one form of central tendency. Not all central tendencies should be considered definitions of average....
of four sound absorption coefficients of the particular surface at frequencies of 125, 250 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, 500 Hz, 1000 Hz, 2000, and 4000 Hz. These frequencies encompass the fundamental frequencies and first few overtones of typical human speech, and, therefore, the NRC provides a decent and simple quantification of how well the particular surface will absorb the human voice
Human voice
The human voice consists of sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc. Its frequency ranges from about 60 to 7000 Hz. The human voice is specifically that part of human sound production in which the vocal folds are the primary...
. A more broad frequency range should be considered for applications such as music or controlling mechanical noise.
Specifications for materials used in sound absorption commonly include an NRC for simplicity, in addition to more detailed frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
vs amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
charts.