Parabolic reflectors
Parabolic reflectors, tape player
Parabolic reflectors

 

Code Number: 3B35.39

Demo Title: Curved Reflectors - Whispering Gallery

Condition: Good

Principle: Group & Phase Velocity

Area of Study: Oscillations & Acoustics

Equipment: 

Parabolic reflectors, tape player.

Procedure:

Attach the tape player to the focal point of one of the reflectors.  Align the reflectors so that they are parallel and some long distance apart (greater than 25 ft.).  When the reflectors are aligned properly the tape player can be turned down to a volume that cannot be heard when standing near the other reflector unless you hold your ear to the focal point of that reflector.

References:

  • Thomas B. Greenslade, Jr., "Whispering Galleries", TPT, Vol. 18, # 1, Jan 1980, p. 52.
  • Thomas B. Greenslade, Jr., "19th Century Textbook Illustrations IV", TPT, Vol. 13, # 9, Dec. 1975, p. 522.
  • Robert H. Johns, "Parabolic Reflectors for Sound", TPT, Vol. 11, # 9, Dec. 1973, p. 567.
  • Jearl Walker, "Some Whispering Galleries Are Simply Sound Reflectors, But Others Are More Mysterious", The Amateur Scientist, Oct. 1978.
  • George M. Hopkins, "Reflection and Concentration of Sound", Experimental Science, p. 158.
  • Pat Murphy, Ellen Macaulay, and the staff of the Exploratorium, "Talk to a Wok", Exploratopia, p. 350.
  • Jearl Walker, "3.63, Whispering Gallery in St. Paul's Cathedral", The Flying Circus of Physics Ed. 2, p. 171.
  • Jearl Walker, "3.62, Whispering Galleries in Various Enclosures", The Flying Circus of Physics Ed. 2, p. 171.
  • Ron Hipschman,  "Focused Sound",  Exploratorium Cookbook II, p. 115.1.