Sound propagation, Reflection and Perception

by Daniel Tay

The focus of my research was on the physics behind the propagation of sound in a small room setting, and how the same sound is perceived by the user. This setting best describes the home environment that our group is designing ‘invisible sound’ for. Such a specification of the room setting is vital, as the acoustics of small spaces defer greatly from that of larger venues such as concert halls.

live_dry

An important aspect of the sound quality is based on perception. Acousticians then conduct experiments to quantify such qualities scientifically. An acoustically good room sounds ‘live’, and the converse, ‘dead’. The most dated method of quantifying this is the Reverberation Time, where a high RT number indicates better acoustic quality. Acousticians such as D’Antonio and Eger (1986); Geddes (2002); Jones (2003); Kuttruff (1998) have questioned this given that smaller rooms typically have smaller RT numbers. They propose that sound reflection takes on even greater importance in the overall listening experience, which brings us to the next section.

 

Toole (2008) talks about the need to delve deeper beyond simple measurements. He too concurs with the former group of acousticians about the influences of early reflected sounds. He further proposes that the knowledge of ‘directivity and off-axis frequency responses of loudspeakers and the directional reflective, diffusive, and absorptive characteristics of materials at the points of first reflections are essential’.

 

Toole (2008) writes about a cognitive effect called the ‘precedence effect’ of the brain localizing in the presence of multiple different sound sources. The results gathered from different research is presented as follows- Firstly, stronger reflections shift the position of the source and make it seem larger. Secondly, reflections and delayed reflections change the timbre of the perceived sound, adding coloration and resonance that may affect the listening experience in both ways. Humans perceive such effects most if the reflections are in the median plane.

pri_sec_image

The timing in between reflections too affect the listening experience. Haas, Gardner, Lochner and Burger all found that the first reflection dominates this experience. However, the timings between subsequent reflections determine if these are heard as ‘spatially separated auditory images’ (long delay) or as a single image (short delay). Also, the volume of the delayed sound determines how ‘spacious’ the room sounds.

image_delay

In relation to our project, it is clear that for an even perception of sound across the entire living space, it is necessary to consider the acoustics of the individual spaces such as the kitchen, bathroom and hallway that make up the entire living space. Factors such as the volume of the room, the presence of strongly sound-absorbing curtains and furniture in the living room in comparison to hard table tops in the kitchen do affect the listening experience. Sound sources should therefore cater for and smoothen out these localized irregularities to create an excellent, across-the-board listening experience. If possible, the sound system could even take advantage of reflections and utilize them to enhance the listening experience.

 

 

References

Acoustics of rooms

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https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.775-3-201208-I!!PDF-E.pdf

 

 

Toole (1986). “Loudspeaker Measurements and Their Relationship to Listener Preferences,”

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http://mariobon.com/Articoli_storici/AES_1986_Toole_01.pdf

http://mariobon.com/Articoli_storici/AES_1986_Toole_02.pdf

 

Schroeder, M.R. (1954). “Statistical Parameters of the Frequency Response Curves of

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http://www.aes.org/e-lib/browse.cfm?elib=9192

 

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http://www.sciencedirect.com/science/article/pii/0003682X83900282

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D’Antonio, P., and Eger, D. (1986). “T60—How Do I Measure Thee, Let Me Count the

Ways,” 81st Convention, Audio Eng. Soc., Preprint 2368.

http://www.aes.org/e-lib/browse.cfm?elib=5062

 

Geddes, E.R. (2002). Premium Home Theater: Design and Construction. GedLee LLC, Novi,

Michigan, USA. www.gedlee.com.

http://www.gedlee.com/downloads/Chapter%204.pdf

 

Jones, D. (2003). “A Review of the Pertinent Measurements and Equations for Small

Room Acoustics,” J. Acoust. Soc. Am., 113, p. 2273 (abstract only). Personal communication:

presentation text from the author.

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Kuttruff, H. (1998). “Sound Fields in Small Rooms,” 15th Conference, Audio Eng. Soc., Paper

15-002.

http://www.aes.org/e-lib/browse.cfm?elib=8106

 

Benade, A.H. (1984). “Wind Instruments in the Concert Hall.” Text of an oral presentation

at Parc de la Villette, Paris; part of a series of lectures entitled “Acoustique,

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Precedence Effect

 

Gardner, M. (1968). “Historical Background of the Haas and/or Precedence Effect,”

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Localization and Listener Perception

 

Gardner, M.  (1969). “Image Fusion, Broadening, and Displacement in Sound Localization,”

  1. Acoust. Soc. Am., 46, pp. 339–349.

http://scitation.aip.org/content/asa/journal/jasa/45/1/10.1121/1.1971974

 

 

 

Gardner, M. (1973). “Some Single- and Multiple-Source Localization Effects,” J. Audio Eng.

Soc., 21, pp. 430–437.

http://www.aes.org/e-lib/browse.cfm?elib=1960

 

Haas, H. (1972). “The Influence of a Single Echo on the Audibility of Speech,” Doctoral

dissertation, University of Göttingen. Reprinted in J. Audio Eng. Soc., 20, pp. 146–

159, 1972. A reprint of a 1949 translation of Haas’s PhD dissertation.
http://www.aes.org/e-lib/browse.cfm?elib=2093&rndx=911823

 

Lochner, J.P.A., and Burger, J.F. (1958). “The Subjective Masking of Short Time-Delayed

Echoes by Their Primary Sounds and Their Contribution to the Intelligibility of

Speech,” Acustica, 8, pp. 1–10.

http://www.ingentaconnect.com/content/dav/aaua/1958/00000008/00000001/art00002

 

Benade, A.H.  (1985). “From Instrument to Ear in a Room: Direct or via Recording,” J. Audio

Eng. Soc., 33, pp. 218–233.

http://www.aes.org/e-lib/browse.cfm?elib=4457

 

Olive, S.E., and Toole, F.E. (1989a). “The Detection of Reflections in Typical Rooms,”

  1. Audio Eng. Soc., 37, pp. 539–553.

http://www.aes.org/e-lib/browse.cfm?elib=6079

 

Shinn-Cunningham, B.G.  (2003). “Acoustics and Perception of Sound in Everyday Environments,” Proc.

3rd Int. Workshop on Spatial Media, Aisu-Wakamatsu, Japan. http://cns.bu.edu/

~shinn/pages/RecentPapers.html.

http://cns.bu.edu/~shinn/pages/pdf/Aizu.pdf

 

Rakerd, B., Hartmann, W.M., and Hsu, J. (2000). “Echo Suppression in the Horizontal

and Median Sagittal Planes,” J. Acoust. Soc. Am., 107, pp. 1061–1064.

http://power.pa.msu.edu/acoustics/hsu.pdf

 

Meyer, E., and Schodder, G.R. (1952). “On the Infl uence of Refl ected Sound on Directional

Localization and Loudness of Speech,” Nachr. Akad. Wiss. Gottingen, Math.

Phys. Klasse IIa, 6, pp. 31–42.

 

Textbook Source

 

Toole, F. E. (2008). Sound reproduction: Loudspeakers and rooms. Taylor & Francis.

https://books.google.com.sg/books?hl=en&lr=&id=sGmz0yONYFcC&oi=fnd&pg=PR3&dq=sound+reproduction+loudspeakers+and+rooms+by+floyd+e+toole&ots=LHDfaq9NoE&sig=PwyJtSVVEiVXyfuLDsazZeeKAr0#v=onepage&q=sound%20reproduction%20loudspeakers%20and%20rooms%20by%20floyd%20e%20toole&f=false

 

 

 

 

 

 

 

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