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The noise reduction coefficient (commonly abbreviated NRC) is a single number value ranging from 0.0 to 1.0 that describes the average sound absorption performance of a material. An NRC of 0.0 indicates the object does not attenuate mid-frequency sounds, but rather reflects sound energy.
The Sound Reduction Index is expressed in decibels (dB). It is the weighted sound reduction index for a partition or single component only. This is a laboratory-only measurement, which uses knowledge of the relative sizes of the rooms in the test suite, and the reverberation time in the receiving room, and the known level of noise which can pass between the rooms in the suite by other routes ...
The method or process of determining the resulting immission level is called noise calculation, its graphical representation is called noise map. Noise calculation is done for the following reasons: to calculate a current situation based on existing physics, mostly when a physical measurement at a location is impractical
It is based on the ASTM E-1332 Standard Classification for Rating Outdoor-Indoor Sound Attenuation. [37] Unlike the STC, which is based on a noise spectrum targeting speech sounds, OITC uses a source noise spectrum that considers frequencies down to 80 Hz (aircraft/rail/truck traffic) and is weighted more to lower frequencies. The OITC value is ...
In the above formula, P is measured in units of power, such as watts (W) or milliwatts (mW), and the signal-to-noise ratio is a pure number. However, when the signal and noise are measured in volts (V) or amperes (A), which are measures of amplitude, [note 1] they must first be squared to obtain a quantity proportional to power, as shown below:
Noise can be an annoyance that creates fatigue and negatively affects productivity, safety and the ability to communicate. Therefore, standard methodologies for quantifying noise have been developed. Noise curves reflect different standardized means of creating a single number rating for the background noise spectrum in a space.
Friis's formula is used to calculate the total noise factor of a cascade of stages, each with its own noise factor and power gain (assuming that the impedances are matched at each stage). The total noise factor can then be used to calculate the total noise figure. The total noise factor is given as
Noise measurement can also be part of a test procedure using white noise, or some other specialized form of test signal.In audio systems and broadcasting, specific methods are used to obtain subjectively valid results in order that different devices and signal paths may be compared regardless of the inconsistent spectral distribution and temporal properties of the noise that they generate.
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