Mystery of the Chirping Pyramid Solved

Ant writes "Nature says the mystery of the 'chirping' pyramid has been decoded. Acoustic analysis shows how the temple transforms echoes into sounds of nature. El Castillo's strange echoes have fascinated visitors for generations. A theory that the ancient Mayans built their pyramids to act as giant resonators to produce strange and evocative echoes has been supported by a team of Belgian scientists."

Comments

You can hear this at Fireworks shows

[wowbagger]

If you go to a fireworks show where there are bleachers nearby, you can hear the same effect - as each retort goes off, you will hear a "fhweeep!" as the impulse from the report crosses the bleachers.

In effect, you are convolving an impulse (the report or hand-clap) with a series of impulses (the steps) to yield a series of impulses.

(and for other signal processing/math pedants out there - yes, a handclap only approximates an impulse, as do the stairs.)

Re:You can hear this at Fireworks shows

[gardyloo]

Hm. Presumably, then, by measuring the spacing between the steps and the fundamental frequency of the sound (maybe with a pitch pipe -- one of the electronic ones for tuning would be even easier), you could measure the speed of sound in air for that day.

God, I'm geeky.

And picket fences, too

[G4from128k]

Walking on gravel next to a picket fence produces similar strange echoes. The fence acts as a grating and the relative angle of the percussive sound waves against the regularly-spaced pickets mean that different frequencies echo from different parts of the fence. The result is a chirping echo that sounds like it is from a moving source.

First hand

[Thyamine]

My wife and I were able to experience this first hand. It's quite amazing to stand in the courtyard in front of the pyramid and do it yourself, although it's more interesting if you believe they did it on purpose. =)

Our tour guide pointed out another similar effect involving The Temple of the Warriors (I believe that was the one) while standing in the same spot. When facing it you can generate the sound of a rattlesnake (open to interpretation of course) which is to praise their sepent god.

The guide also said that priests standing in the temple atop the pyramid would only be able to be heard by someone standing in the correct spot in the courtyard. We didn't get to test that ourselves, but is something I had wanted to find out more about.

Bird calls designed to resemble Mayan echos

[goombah99]

Perhaps they have it all backwards. Bird calls are picked by birds on the basis of many factors. Beyong the obvious need to differentiate for sexual selection and niche indentity there are practical consideration on how they differentiate.

For example, do you want to optimize your call so that it travels well over water, through bushes, in heavy winds, tree-tops, urban landscapes? Maybe you want it not to travel far or make it hard to echo-locate for predator avoidance? Finally there is the problem of modulation.

Presumably you want to embedd information on the call. So you want to choose a family of calls which are easy to generate and modulate.

Sure you could devise an arbitrarily complex voice box to generate any particular coding scheme, but why not instead pick some crude but reliable mechnism with the minimum number of nerve and muscle controls.

Perhaps also efficiency and strain are issues as well.

The bottom line is that perhaps the regular step arrays that can turn an impulse like a hand clap into a characterisitic modulated sound are exactly the same proces by which birds turn a pulse of breath into a modulated bird call? If so it would be unsurprising for artifical geometric structres to produce "bird noises" to the human ear.