Acoustic Mirrors
Figure 1. A sound mirror.Copyright 2009 Bodacea, Wikimedia Commons https://commons.wikimedia.org/wiki/File:Round_acoustic_mirror_-Denge_-Kent_-England-19July2009.jpg
Students play and record the “Mary Had a Little Lamb” song using musical instruments and analyze the intensity of the sound using free audio editing and recording software. Then they use hollow Styrofoam half-spheres as acoustic mirrors (devices that reflect and focus sound), determine the radius of curvature of the mirror and calculate its focal length. Students place a microphone at the acoustic mirror focal point, re-record their songs, and compare the sound intensity on plot spectrums generated from their recordings both with and without the acoustic mirrors. A worksheet and KWL chart are provided.
Acoustic engineering is a branch of engineering that deals with the analysis and control of sound and vibration (such as, sound reduction or noise control) in designs, including noise barriers and sound absorbers, as well as other sound applications, such as concert hall acoustics, medical applications of ultrasound, and public announcement systems. During World War I, the British army depended on acoustics to protect its country from German aircraft; and scientists used acoustics mirrors to detect enemy planes approaching England. In this activity, students use acoustic mirrors and study their impact on the sound intensity of a song.
After this activity, students should be able to:
- Determine the radius of curvature of a concave mirror.
- Calculate the focal length of a concave mirror.
- Analyze the sound intensity of plot spectrums.