Room Acoustics and Materials

By Tan Wei Xian Rachel

My research revolves around understanding room acoustics and materials, extending into acoustically diffusing materials, propagating and insulating materials. Ideally, a living space such as a house should not be acoustically dead, i.e. having no reverberation. (Asselineau, 2015; Kleiner and Jiri, 2014) Appropriate amount of reverberation vary with the applications, for example when singing, a long reverberation time is required. For speech however, a short reverberation time is needed to ensure intelligibility. (Everest et al, 2001; Kuttruff, 2009) There is general agreement that “early reflections” are favourable to both speech and music, reduction of late reflections made possible by rapidly reducing or diffusing the sound after the first few reflections. (Kleiner and Jiri, 2014; Schroeder, 1966) Should the project delve into home cinema territory, it is essential that we design for early reflections.

Sound behaves similarly to light, hence when testing the geometry of a room, ray tracing can be used to study the reflections on wall surfaces. (Kleiner and Jiri, 2014)room acoustics1

Sound propagation along a curved surface, i.e. vaulted ceilings in the past, are efficient in amplifying or maintaining the speed of the sound waves by concentrating the waves at a single receiver. As such the geometry of the room can be manipulated to be directed at a single point.

room acoustics2

Acoustic absorbers and insulators are typically used in music-related applications, helping to sound-proof and reduce the reverberation time of sound waves passing through the medium. These absorbers and insulators are typically porous and/or perforated, never with smooth surfaces. (Hall et al, 2012) Sound waves, as a result, rapid lose energy as they pass through these materials. With effective absorption of sound however, the room sound too dry to the listener. Examples of absorbers are foams, fibrous materials like cushions or glass wool and natural absorbers like earth. (Ingård and Bolt, 1951) There is more research going into granular materials and composite materials.

Diffusion of sound happens when the sound waves hit non-uniform and uneven surfaces, whereby the reflecting wave goes off in many different directions all at once. Diffusers are used as complements to absorbers, ensuring that the sound is evenly distributed across the space. (Chlop, 1992, Strube, 1981). Diffusers range from complex geometrical surfaces to simple cloths and membranes. Wood is also a popular material especially in the field of music. (Asselineau, 2015)

With electroacoustic systems, it is often easier to increase the number of sources instead of propagating the sound via material means. Electroacoustic systems with a large number of sources, i.e. speakers, however, have to be in a room that has as little reverberation time as possible. The sources may interfere with each other otherwise, causing the sound to be interpreted as noise. (Kuttruff, 2009) A delay may be programmed into the second speaker with reference to the location of the receiver/listener, as speakers with the same frequency at the same velocity may end up interfering with each other.

References

  1. Asselineau, Marc. Building Acoustics. Print. CRC Press, 2015. (Room Acoustics) (Acoustics) (Building Acoustics) (Music and Concert Facilities)
  2. Chlop, Bernard W. “Two dimensional sound diffusor.” U.S. Patent No. 5,160,816. 3 Nov. 1992. (Source)
  3. Everest, Frederick Alton, and Ken C. Pohlmann. The master handbook of acoustics. Vol. 4. New York: McGraw-Hill, 2001. (Source)
  4. Fahy, Frank J., and Paolo Gardonio. Sound and structural vibration: radiation, transmission and response. Academic press, 2007. (Source)
  5. Guyot, Nicolas, et al. “Acoustic resonator/diffuser system and method.” U.S. Patent Application No. 10/897,701. Source
  6. Kleiner, Mendel, and Jiri Tichy.Acoustics of small rooms. CRC Press, 2014.
    (Geometrical Acoustics) (Sound Absorption in Rooms)
  7. Kuttruff, Heinrich. Room acoustics. CRC Press, 2009. (Source)
  8. Kuttruff, Heinrich, and Eckard Mommertz. “Room acoustics.”Handbook of Engineering Acoustics. Springer Berlin Heidelberg, 2013. 239-267. (Source)
  9. Hall, Matthew R., Rick Lindsay, and Meror Krayenhoff, eds. Modern earth buildings: Materials, engineering, constructions and applications. Elsevier, 2012. (Source)
  10. Ingård, U., and R. H. Bolt. “Absorption characteristics of acoustic material with perforated facings.” The Journal of the Acoustical Society of America 23.5 (1951): 533-540. (Source)
  11. Lemaitre, Guy. “Flat acoustic diffuser.” U.S. Patent No. 4,566,557. 28 Jan. 1986. (Source)
  12. Liu, Chu-heng, and Sidney R. Nagel. “Sound in a granular material: disorder and nonlinearity.”Physical Review B 21 (1993): 15646. (Source)
  13. Pierce, Allan D. Acoustics: an introduction to its physical principles and applications. Vol. 20. New York: McGraw-Hill, 1981. (Source)
  14. Scott, R. A. “The propagation of sound between walls of porous material.” Proceedings of the Physical Society 58.4 (1946): 358. (Source)
  15. Schroeder, M. R.. “Architectural Acoustics”. Science 151.3716 (1966): 1355–1359. (Source)
  16. Strube, Hans Werner. “More on the diffraction theory of Schroeder diffusors.” The Journal of the Acoustical Society of America 70.2 (1981): 633-635. (Source)
  17. Taguchi, Kazunori. “Sound absorbing and diffusing unit, an acoustic screen and a decorative sound absorbing panel.” U.S. Patent No. 4,207,964. 17 Jun. 1980. (Source)
  18. Sound Diffusion
  19. Sound Diffuser Material
  20. Sound Diffusers
  21. Reflection, Diffusion and Absorption of Sound
  22. Acoustics for Beginners