The Look of Sound: Acoustic Cancellation in Architecture Cameron McCord, Department of Engineering Technology, College of Engineering and Honors College Mentor: Dr. Samuel Matteson, Department of Physics, College of Arts and Sciences

Key Terms Sound - perception of compressional waves traveling through a medium Architectural Acoustics – study of controlling sound within buildings Wave Cancellation – occurs when the sum of waves is less than their added magnitudes Cancellation of waves When two waves of opposite phase and equal amplitude meet (A&B), the resultant is the cancellation of both (C) 2

Research Questions How are sound waves modeled on a computer? What characteristics of certain sounds lead to cancellation? What levels of sound intensity are needed for clear perception? In what ways can structures be built or modified to produce audible and useful sound? 3

Difficulties with Transmission Oddly sized structures Absorptive or reflective materials Background noise Other sound sources Lack of good hearing Repetitive structures The diffusion of sound around a barrier The sound waves are partially blocked by the barrier, then diffuse on the other side. 4

Acoustic Cancellation Two or more waves meet, decrease intensity Usually occurs when structures are spaced at half wavelengths of the sound With periodically placed structures, creates a “stop-band” or “band-gap” filter Cancellation The source (dark circle) sends sound directly to the receiver (white circle) and by reflecting from the top. If the distance between the absorptive surfaces on the ceiling is a certain interval, the sound will cancel at the receiver. 5

Acoustic Cancellation Band-gap filter blocks only a certain range of frequencies and passes all others Magnitude Half-power 6

Acoustic Cancellation Areas of high amplitude (good transmission) and areas of near zero amplitude (cancellation) in a generic room 7

Evenly spaced holes block low frequency sound from trains Methodology Create a PVC pipe with variably spaced holes Put white noise and a frequency sweep of the tube at each interval Determine which frequencies pass and which are blocked Establish a model for which frequencies pass in relation to the spacing of the holes Measure existing buildings with filtering effects DC Metro Line Evenly spaced holes block low frequency sound from trains 8

Other Concerns Large machinery Repeatability of data Physics Student Shop Repeatability of data Will certain frequencies always be blocked? 9

Brief Bibliography Carvalho, Antonio P. O. and Anabela P. B. Carvalho. "Acoustic Characterization of Historic Cloisters in Portugal." Proceedings of the NoiseCon04. Baltimore, MD: National Conference of Noise Control Engineering, 2004. Lanbo Liu, and Donald G. Albert. "Acoustic Pulse Propagation Near a Right-Angle Wall." Journal of the Acoustical Society of America 119, no. 4 (April 2006): 2073-2083. Academic Search Complete, EBSCOhost (accessed October 6, 2007). Matteson, Samuel, interview by Cameron McCord. Acoustics Research Methodology (October 18, 2007). Petra, Larm, and Valtteri Hongisto. "Experimental Comparison Between Speech Transmission Index Rapid Speech Transmission Index and Speech Intelligibility Index." Journal of the Acoustical Society of North America, 2006: 1106-1117.

Acknowledgements Dr. Samuel Matteson, Department of Physics Dr. Susan Eve, Honors College Dr. Gloria Cox, Honors College You, supporting undergraduate research 11

Questions (and Answers) Thank You! 12