Thursday, February 16, 2012

Mystical Sound, Physics Phenomenon, or Both?

Since 1997, residents and tourists alike have reveled in a mysterious sound emanating from a Chinese square. When fireworks are set off near the Southern Jiangsu Victory Monument, a seconds long echo — that sounds uncannily like a bugle — can be heard.

Some attributed spiritual significance to the sound because of the monument's proximity to a sacred Taoist mountain. Scientists, however, have found that there's a straightforward physics explanation behind the bugle-like sound.

You can hear the bugle-like sound after every fireworks "pop" in the video below.


Video courtesy Sihui Wang of Nanjing University in China.


Sihui Wang and colleagues from Nanjing University in China set out to unravel the mystery behind the "Maoshan Bugle." Local media had found no physical explanation for the bugle sound for years, prompting the research team to examine the square more closely.

The square has six sets of approximately 50 steps around it. And the team found that this grating structure of steps created an interference effect when when the fireworks sounds bounced off of the steps.

The team recreated a theoretical model of the grating structure, and found that it produced a similar bugle-like echo as well. Thus, the team has shed some light on the mystical Maoshan bugle.

"The physics is not mysterious after revelation," Wang told Physics Central in an email.

Wang hoped to present his research during the American Physical Society's upcoming March Meeting in Boston. Unfortunately, he won't be able to make the trip over to the U.S., and his talk has been withdrawn. Nonetheless, Wang still wants to share his unique discovery with the public.

3 comments:

  1. Neighborhood After School Science AssociationFebruary 17, 2012 at 6:01 AM

    There is a tv science special about a similar place in the jungle - Mayan we think that has a similar situation. Ancient priests would clap their hands and the echo back of a sacred bird occurred thought to be from the steps on a pyramid

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  2. I noticed this before..
    While doing a flight line security watch..... Sharp sounds would have a tone in their echo, that would shift in frequency when I walked in different directions..

    I finally resolved it was the vertically corrugated metal on the side of the hangar, as it echoed off each corrugation it ended up returning a pulsed echo..

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    Replies
    1. Congratulations to Sihui Wang and his colleagues at Nanjing University for their physical explanation of the "Maoshan Bugle".

      In 1998 I discovered a similar mysterious sound at Chichen Itza, Mexico: a "chirped echo" stimulated by hand-claps at a Maya pyramid. The chirp's sound and sonogram matched the resplendant quetzal - a bird revered by the Maya since ancient times.

      Like Sihui Wang and his colleagues, and Stroh Bing, I found a physical explanation.

      Downward chirped echoes are returned from a pyramid staircase of 91 steps. Recordings can be heard at http://www.ocasa.org/membersites.htm

      The "Maoshan bugle" is stimulated by impulsive firework sounds. Evidently one can account for the mysterious bugle sound satisfactorily as diffraction from the 50 steps in the square. (I expect you will find that sound is harmonic-rich as well.)

      The "chirped" Mexican echoes span a frequency range of up to 41% when the clapper is close to the pyramid. Probably, the chirp occurs because the impulse impingement angles vary over a larger range in Mexico than in China. That's because the hand-clap sound source is much closer to the temple staircase in Mexico than the firework explosions are to the Victory monument staircase in China.

      A more complete explanation for the Mexican chirped echo makes use of impulse response/convolution methods. Convolving the hand-clap time signature with the staircase impulse response yield echo sonograms that closely agree with site measurements.

      Some archaeologists believe this to be the most convincing example of intentional acoustic design by ancient builders. It has helped to stimulated growth of the emergent field of "archaeoacoustics".

      The "spiritual significance" that Taoists attribute to the bugle sound does not surprise me. The chirped echo in Mexico has a religious significance to the Maya as well. A close connection between sound and spirit is often noted at sacred sites. That connection rightly interests students of religious experience, including anthropologists.

      David Lubman, FASA, FINCE
      Acoustical Scientist/Consultant
      dlubman@dlacoustics.com

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