NIC | Noise Isolation Class; a single number noise reduction rating of a partition, room or enclosure where sound pressure level differentials are measured in one-third octave bands and compared with standard contours as per ASTM E 413 |

NMR | Nuclear Magnetic Resonance; commonly used in describing research MRI systems |

NR | Noise Reduction; the difference in sound pressure level between any two points along the path of sound propagation. As an example, noise reduction is the term used to describe the difference in sound pressure levels between the inside and outside of an enclosure. Noise reduction is usually expressed as a function of full octave or one-third octave bands |

NRC | Noise Reduction Coefficient; the arithmetic average, to the nearest multiple of 0.05, of the sound absorption coefficients in the one-third octave bands centered at 250 Hz, 500 Hz, 1,000 Hz, and 2,000 Hz. By convention, the maximum NRC used is 0.95, even though the published laboratory average may be greater |

OBO | Overseas Building Operations |

RFI | Radio Frequency; any frequency at which coherent electromagnetic radiation of energy is possible. Generally considered to be any frequency above 10 kHz |

RFI | Radio Frequency Interference; relates to MIL F 15733 |

SCIF | Secure Compartmented Information Facility; relates to DCID 6/9 |

SCR | Secure Conference Room |

SPL | Sound Pressure Level; the ratio, expressed in decibels, of mean-square sound pressure to a reference mean-square pressure which by convention has been selected to be equal to the assumed threshold of hearing |

STC | Sound Transmission Class; a single number decibel rating of the transmission loss properties of a partition. Measured transmission loss data is plotted versus frequency and compared with standard contours according to rules outlined in ASTM E 90 and ASTM E 413 |

STL | Sound Transmission Loss; a logarithmic ratio of the sound power incident on one side of a partition to the sound power transmitted on the other side. STL is usually rated in one-third octave bands or full octave bands |