1. 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

2. 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

3. 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

4. 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

5. 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

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

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

8. 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

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

10. 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): 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:

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

12. Questions
(and Answers)
Thank You! 12