Noise Curves

Noise Curves

Noise curves specify the acoustic ambient noise in an indoor environment. The unoccupied room is measured to produce a single maximum value across the complete sound spectrum. This value is used to determine if the ambient noise will be annoying to people occupying the room. The value also influences the intelligibility of speech.

At a glance

  • Noise Criteria NC (ANSI S12.2-2008)
  • Room Noise Criteria RNC (ANSI S12.2-2008)
  • Noise Rating NR (ISO 1996)


Different rooms, locations, regulations and applications may allow different acceptable noise ratings. In most cases, the goal is that background noise should not interfere with the purpose of the room, e.g. the noise of an office air-conditioning system and consistent noise of traffic outside the building should not interfere with telephone calls or conversations.

Background noise that is annoying creates fatigue and can negatively affect productivity and safety. Too much noise also affects the ability to communicate. Therefore standard methodologies for quantifying such noise have been developed.

Methods and Standards

For all ambient noise measurement methods, a measured noise spectrum is superimposed on a family of contours (or curves).

NC Result
Result: NC45


Read more about Noise Curves

Measuring Noise Curves with the XL2 Analyzer

The XL2 Acoustic and Audio Analyzer, with the Spectral Limit Option installed, supports these Noise Curve types:

NC Result

The XL2 measures all noise curve types at the same time, thus you can switch to your required report after the measurement. The result also indicates the frequency band with the highest noise rating between 16 Hz and 8 kHz.

For RNC curve types the XL2 reports any large fluctuations or surging at low frequencies, e.g. caused by fans.

Further following the RNC specification, the XL2 measures the octave-band sound pressure level every 100 ms. The minimum measurement time is 20 seconds.

For curve types NC-2008 and NC-1995, the speech interference level (SIL) result is calculated by averaging the octave-band sound pressure levels at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The XL2 Analyzer includes any tangency method adaptation as applicable.



Exel Set for Noise Curves Testing

Exel Kit for Noise Curves Measurements

  • XL2 Audio and Acoustic Analyzer
  • Spectral Limits Option for XL2
  • M2211 Measurement Microphone
  • ASD Cable for XL2
  • Mains Power Adapter
  • 2x Calibration Certificates
  • Exel System Case

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