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Narrow-band analyzer |
| An analyzer whose bandwidth for analysis of sound is less than one-third octave in width. The bandwidth may be a percentage of the center frequency or a fixed number of frequencies in hertz. |
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NCA curves |
| NC curves which have higher octave-band sound pressure levels in the lower frequencies. These curves have been superceded by the PNC curves. |
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NC curves |
| A set of curves used to rate sounds. The curves give octave-band sound pressure levels for each of the ratings which are in 5 dB steps. The curves were developed using octave bands with frequency limits which are no longer used. They have been superceded by the PNC curves. |
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Noise isolation class (NIC) |
| A rating curve for sound isolation analagous to the sound transmission class curve. The NIC curve is intended for use when the sound isolation is measured in the field rather than in the laboratory. |
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Noise |
| Unwanted sound. This term is loosely used for sound. A sound can be noise at times and not at others. |
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Noise level (dBA) |
| A term used interchangeably with sound level. The term implies the A-weighted sound level |
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Normal incidence sound absorption (alpha n) |
| The sound absorption of a material when the sound wave is normally incident upon the material. (Normal means that the direction of sound propagation is perpendicular to the material.) |
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Noise reduction (NR, dB) |
| The arithmetic difference in decibels between the levels measured on either side of a noise control device. This could be a muffler in a duct system, a barrier, or a wall separating two spaces. |
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Noise reduction coefficient (NRC) |
| The arithmatic average of the sound absorption coefficients measured at 250, 500, 1000, and 2000 Hz in according with ASTM Designation: E 423. |
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NRC |
| (see Noise reduction coefficient) |
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