Room acoustics

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Room acoustics is a subfield of acoustics dealing with the behaviour of sound in enclosed or partially-enclosed spaces. The architectural details of a room influences the behaviour of sound waves within it, with the effects varying by frequency. Acoustic reflection, diffraction, and diffusion can combine to create audible phenomena such as room modes and standing waves at specific frequencies and locations, echos, and unique reverberation patterns.

Contents

Frequency zones

The way that sound behaves in a room can be broken up into four different frequency zones:

Natural modes

The pressure of axial modes (top row) and tangential modes (bottom row) plotted for modal numbers (m = 0, 1) and (n = 1, 2, 3) Tangential Room Modes.jpg
The pressure of axial modes (top row) and tangential modes (bottom row) plotted for modal numbers (m = 0, 1) and (n = 1, 2, 3)

For frequencies under the Schroeder frequency, certain wavelengths of sound will build up as resonances within the boundaries of the room, and the resonating frequencies can be determined using the room's dimensions. Similar to the calculation of standing waves inside a pipe with two closed ends, the modal frequencies and the sound pressure of those modes at a particular position of a rectilinear room can be defined as

where are mode numbers corresponding to the x-,y-, and z-axis of the room, is the speed of sound in , are the dimensions of the room in meters. is the amplitude of the sound wave, and are coordinates of a point contained inside the room. [4]

Modes can occur in all three dimensions of a room. Axial modes are one-dimensional, and build up between one set of parallel walls. Tangential modes are two-dimensional, and involve four walls bounding the space perpendicular to each other. Finally, oblique modes concern all walls within the simplified rectilinear room. [5]

A modal density analysis method using concepts from psychoacoustics, the "Bonello criterion", analyzes the first 48 room modes and plots the number of modes in each one-third of an octave. [6] The curve increases monotonically (each one-third of an octave must have more modes than the preceding one). [7] Other systems to determine correct room ratios have more recently been developed. [8]

Reverberation of the room

After determining the best dimensions of the room, using the modal density criteria, the next step is to find the correct reverberation time. The most appropriate reverberation time depends on the use of the room. RT60 is a measure of reverberation time. [9] Times about 1.5 to 2 seconds are needed for opera theaters and concert halls. For broadcasting and recording studios and conference rooms, values under one second are frequently used. The recommended reverberation time is always a function of the volume of the room. Several authors give their recommendations [10] A good approximation for broadcasting studios and conference rooms is:

TR[1 kHz] = [0.4 log (V+62)] – 0.38 seconds,

with V=volume of the room in m3. [11] Ideally, the RT60 should have about the same value at all frequencies from 30 to 12,000 Hz.

To get the desired RT60, several acoustics materials can be used as described in several books. [12] [13] A valuable simplification of the task was proposed by Oscar Bonello in 1979. [14] It consists of using standard acoustic panels of 1 m2 hung from the walls of the room (only if the panels are parallel). These panels use a combination of three Helmholtz resonators and a wooden resonant panel. This system gives a large acoustic absorption at low frequencies (under 500 Hz) and reduces at high frequencies to compensate for the typical absorption by people, lateral surfaces, ceilings, etc.

Sound treatment variations:
* Grey: absorption
* Black: reflection
* Blue: diffusion Sound treatment.svg

Sound treatment variations:
• Grey: absorption
• Black: reflection
• Blue: diffusion

Acoustic space is an acoustic environment in which sound can be heard by an observer. The term acoustic space was first mentioned by Marshall McLuhan, a professor and a philosopher. [15]

Nature of acoustics

In reality, there are some properties of acoustics that affect the acoustic space. These properties can either improve the quality of the sound or interfere with the sound.

Uses of acoustic space

The application of acoustic space is very useful in architecture. Some kinds of architecture need a proficient design to bring out the best performances. For example, concert halls, auditoriums, theaters, or even cathedrals. [18]

Interior view of Mabel Tainter Theater Interior of Mabel Tainter Theater.jpeg
Interior view of Mabel Tainter Theater
Interior view of the choir at Worcester Cathedral, Worcestershire, UK Worcester Cathedral choir, Worcestershire, UK - Diliff.jpg
Interior view of the choir at Worcester Cathedral, Worcestershire, UK

Planning the acoustics of the room

The acoustic impression of a room is determined by:

The task of room acoustics is to influence these parameters by designing the room [24] in such a way that the acoustic properties of the room are maximized for its intended use. However, not all venues are designed with acoustics in mind. In this case, speaker placement will play a decisive role in the movement of sound waves, affecting clarity, loudness and overall sound quality. [25]

The goals of acoustical room design can be: [26]

Since the acoustic properties of rooms for different applications are almost incompatible, it is hardly possible to create a universal room that combines good speech intelligibility and good spatial music perception.

See also

Notes

  1. The frequency is approximately  Hz when room volume, V, is measured in cubic metres, and reverberation time, RT60, is measured in seconds; this formula incorporates the approximate speed of sound in air. [1] [2]

References

  1. Schroeder, Manfred (1996). "The 'Schroeder Frequency' Revisited" . Journal of the Acoustical Society of America. 99 (5): 3240–3241. Bibcode:1996ASAJ...99.3240S. doi:10.1121/1.414868.
  2. Davis, Don; Patronis, Eugene; Brown, Pat (2013). Sound System Engineering (4 ed.). p. 215.
  3. Crocker, Malcolm J. (2007). Handbook of Noise and Vibration Control. p. 54.
  4. Fidecki, Tadeusz. "Room Acoustics and Sound Reinforcement Systems". pp. Section 1.1.
  5. Larsen, Holger (1978). Reverberation Process at Low Frequencies (PDF). Bruël and Kjaer Technical Review No. 4. Bruël and Kjaer.
  6. Bonello, Oscar J. (1981). "A New Criterion for the Distribution of Normal Room Modes". Journal of the Audio Engineering Society. 29 (9): 597–606.
  7. Ballou, Glen. Handbook for Sound Engineers. Howards Sams. p. 56.
  8. Cox, T. J.; D'Antonio, P.; Avis, M. R. (2004). "Room Sizing and Optimization at Low Frequencies". Journal of the Audio Engineering Society. 52 (6): 640–651.
  9. "RT60 Reverberation Time" . Retrieved 2024-03-27.
  10. Beranek, Leo (1954). "Chapter 13". Acoustics. McGraw Hill Books.
  11. Bonello, Oscar. Clases de Acústica. Edited CEI, Facultad de Ingeniería UBA.
  12. Rettinger, Michael (1977). Acoustic Design and Noise Control. New York: Chemical Publishing.
  13. Knudsen, Vern Oliver; Harris, Cyril M. (1965). Acoustical Designing in Architecture . New York: John Wiley and Sons.
  14. Bonello, Oscar (1979). A new computer aided method for the complete acoustical design of broadcasting and recording studios. International Conference on Acoustics, Speech and Signal Processing, ICASSP '79. Washington: IEEE.
  15. Schafer, R. M. (2007). "Acoustic Space". Circuit. 17 (3): 83–86. doi: 10.7202/017594ar .
  16. 1 2 3 Knudsen, V.; Harris, C. (1950). Acoustic Designing in Architecture. The American Institute of Physics. pp. 1–18, 112–150.
  17. Smitthakorn, P.; Siebein, G. (2012). Diffuse Reflection: Architectural Acoustics Effects of Specular & Diffuse Reflections on Perceived Music Quality. Saarbruecken, Germany: Lap Lambert Academic Publishing. pp. 11–19.
  18. Cavanaugh, W.; Tocci, G.; Wilkes, J. (2010). Architectural Acoustics Principles and Practice. In Marshall, L. (ed.) Acoustical Design: Places for Listening. New Jersey: John Wiley & Sons. pp. 133–157.
  19. 1 2 Long, M. (2006). Architectural Acoustics. In Levy, M. & Stern, R. (ed.) General Consideration: Design of Rooms For Music. The United States of America: Elsevier Inc. pp. 653–656.
  20. "Glossary WiSound Listen & You'll See!". wisound.com. Retrieved 2025-04-19.
  21. "Odeon Room Acoustics Software". odeon.dk. Retrieved 2025-04-19.
  22. "Fundamentals Of Room Acoustics" (PDF). www.arauacustica.com. Retrieved 2025-04-19.
  23. Morgenstern, Hai; Rafaely, Boaz; Zotter, Franz (2015). "Theory and investigation of acoustic multiple-input multiple-output systems based on spherical arrays in a room". The Journal of the Acoustical Society of America. 138 (5): 2998–3009. arXiv: 2401.03493 . Bibcode:2015ASAJ..138.2998M. doi:10.1121/1.4934555. PMID   26627773.
  24. Shtrepi, Louena; Aletta, Francesco; Aspöck, Lukas; Astolfi, Arianna; Fels, Janina; Hornikx, Maarten; Jambrošić, Kristian; Jeong, Cheol-Ho; Kahle, Eckhard; Llorca-Bofí, Josep; Rindel, Jens Holger; Rychtáriková, Monika; Torresin, Simone; Vorländer, Michael (November 2024). "Ten questions concerning Architectural Acoustics". Building and Environment. 265 112012. Bibcode:2024BuEnv.26512012S. doi:10.1016/j.buildenv.2024.112012.
  25. "The Science of Sound: How Speaker Placement Impacts Audio Quality". westwaveav.com. 22 February 2025. Retrieved 2025-04-19.
  26. "10 Acoustic Design Principles to Consider in Your Next Project". gbdmagazine.com. 24 November 2023. Retrieved 2025-04-19.
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