Indoor Environmental Quality Guidelines

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I.7 Effective Acoustics

Provide interior conditions that avoid harmful noise effects and produce a basis for a positive soundscape acceptable to occupants and appropriate to their tasks. The benefits are avoiding exposure to: unhealthy noise levels, the elevated stress which accompanies higher background noise levels and noise distraction impacts on mental work. Effective acoustics enable effective speech communications at normal speaking voice while providing for local speech privacy.

Required Performance Criteria
Prevent Harmful Acoustic Conditions

  1. Recurrent background noise from external and internal sources shall not exceed 70 dBA.
  2. All continuously occupied office space shall meet a NC (Noise Curve) of no greater than NC-50. (See recommended levels below.)
  3. All classroom space shall meet an NC of no greater than NC-45.(See recommended levels below.)
  4. Reverberation time for all continuously occupied space shall be no less than 0.2 sec and no greater than 0.8 sec. Reverberation time shall be based on the 500 Hz octave band, and shall be appropriate to the uses of the space. (See recommended levels below.) Note that this requirement would not apply to concert halls or other music performance auditoria.

Recommended Performance Criteria

  1. Articulation Index shall be less than 0.20 for open offices, where a low level of speech intelligibility is required (speech privacy is desired), and greater than 0.70 for enclosed offices where a high level of speech intelligibility is required.

Promote Positive Acoustics Appropriate to Tasks:

  1. Reduce NC criterion to NC 45 or lower for continuously occupied spaces.
  2. NC shall be no greater than NC 40 for intermittently occupied meeting spaces like conference rooms and classrooms. (Note that this is less stringent than the ANSI S12.60 standard for classrooms.)
  3. Provide Reverberation Times optimal for space use based on professional acoustic judgment. General Guidelines are as follows:
    • Open Office: 0.2-0.5 seconds
    • Enclosed offices: 0.2-0.4 seconds
    • Classrooms 0.2-0.7 seconds
    • For other space types, such as gymnasiums and auditoriums, use acoustic professional judgment and advice.

Compliance Tools and Resources

  • Professional acoustical advice and consulting
  • Acoustics modeling and analysis software programs.

Related MSBG Documents

Supplemental Resources

  • There are several US University programs focused on architectural acoustics and many sources of room acoustics modeling software that are commercially available. There are also free acoustics modeling and analysis software programs available from some universities and companies. These programs provide calculated estimates of quantities like reverberation time and sound pressure levels given certain parameters that account for room size, shape, surface absorption and activity types.
  • Very informative introductions to room acoustics modeling are given by Lokki & Jarvelainen, (2001) and Rindel, (2000.) A very helpful, illustrated, online PowerPoint presentation that includes room acoustics modeling is given by Lokki & Savioja (2002.) The University of California at Berkeley, The Rensselaer Technical Institute, and McGill University all have extensive online resources available on architectural acoustics.

Helpful Internet resources include:

Other Supplemental Resources

  • Bechtel, Robert B. & Churchman, Azra, (Eds.) (2002) Handbook of Environmental Psychology. John Wiley & Sons, NY.
  • Boff, K. & Lincoln, J. (Eds.) (1988) Engineering Data Compendium: Human Perception and Performance. Harry G. Armstrong Aerospace Medical Research Laboratory, Wright Patterson AFB, Ohio.
  • Harris, C. M. (1979) Handbook of Noise Control. McGraw-Hill, New York.
  • Hass, Ellen, & Edworthy, Judy (Eds.) (2002) The Ergonomics of Sound. Human Factors & Ergonomics Society, Santa Monica, CA.
  • Lokki, T. & Jarvelainen Hanna, (2001) Proceedings of the 2001 International Conference on Auditory Display, July 29-August 1, 2001. Pgs. 26-31 Espoo, Finland. (Available online.)
  • Lokki, T. & Savioja, L. (2002) VR Research at HUT and Real-Time Auralization. Future Workplaces, Stuttgart, 10-11 October 2002. (Available online.)
  • NASA (1995) Man-System Integration Standards. Johnson Space Center, Houston, TX.
  • Rindel, J.H. (2000) The use of computer modeling in room acoustics. Journal of Vibroengineering. No. 3(4) Index 41-72. (Available online)
  • Salvendy, Gavriel (Ed.) (1987) Handbook of Human Factors. John Wiley & Sons, NY.
  • Watson, Donald. Crosbie, Michael. Crosbie, Michael J. & Callender, Michael H. (1997.) Time-Saver Standards for Architectural Design Data. McGraw-Hill, NY.
  • Wise, James. The Human Nature of Noise and Vibration. Eco-Integrations, Inc.
  • Woodson, W. E, Tillman, P. & Tillman, B. (1992) Human Factors Design Handbook, 2nd Edition. McGraw-Hill, NY.

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