On summer 08 we packed our children and a few of our belongings and headed towards the Yucatan Peninsula, Mexico on a Continental aircraft. As other tourists we occupied ourselves with minor issues such as what to order for lunch-Inchiladas or Fajitas, what is the best way to reach the next Maya site and whether to take a tour guide. After some negotiations we decided to take guides in the most famous sites-Chichen Itche and Uxmal.
One of he most impressive things in the tour was the bird sound, the pride of the tour guides. When standing at some distance from the Grand Pyramid in Chichen Itche and clapping hands a bird sound echo is heard. Hundreds of ecstatic tourists stand at some distance from the pyramids clapping hands, in order to hear the echo that sounds like a bird. The tour guides tell that the Mayas were experts in acoustics and that they build the pyramids in such a way that a special sound is heard at the clap of hands. They also say that the secret of the acoustic infrastructures was not yet revealed.
We returned to our homeland, Israel and to our busy everyday life. As to our trip to Mexico, the unresoved bird voice still echoed in our memory as one of the more exciting things that we have experienced in the Yucatan Peninsula. On the holy day of Kipur, when the day was at its end, my son and I went out on a walk in order to witness the last bicycles and roller blades riders that filled the streets during the entire day.
My son that since our trip to Mexico developed a new habit of clapping hands once in a while in order to hear if an echo is heard, had practiced his habit exactly when standing at the front of a waved metal wall. To our astonishment we heard the bird sound. It took us a few days to grasp the full meaning of our discovery - The waves of the wall like the stairs of the pyramids created the echo of the bird sound.

And the scientific part:
Sound produces echo when reflecting from a distant surface, as we hear when shouting near a mountain or into a well. We are used to hear the same sound, with a delay correponding to the distance of the reflecting surface.
However a surprising phenomena happens if the reflecting surfaces are closer to one another - which is the case near a Mayan pyramid.
To demonstrate this we have simulated a pyramid on our PC. First, we have recorded the sound of one clap (Fig 1). It sounds like that:
One of he most impressive things in the tour was the bird sound, the pride of the tour guides. When standing at some distance from the Grand Pyramid in Chichen Itche and clapping hands a bird sound echo is heard. Hundreds of ecstatic tourists stand at some distance from the pyramids clapping hands, in order to hear the echo that sounds like a bird. The tour guides tell that the Mayas were experts in acoustics and that they build the pyramids in such a way that a special sound is heard at the clap of hands. They also say that the secret of the acoustic infrastructures was not yet revealed.
We returned to our homeland, Israel and to our busy everyday life. As to our trip to Mexico, the unresoved bird voice still echoed in our memory as one of the more exciting things that we have experienced in the Yucatan Peninsula. On the holy day of Kipur, when the day was at its end, my son and I went out on a walk in order to witness the last bicycles and roller blades riders that filled the streets during the entire day.
My son that since our trip to Mexico developed a new habit of clapping hands once in a while in order to hear if an echo is heard, had practiced his habit exactly when standing at the front of a waved metal wall. To our astonishment we heard the bird sound. It took us a few days to grasp the full meaning of our discovery - The waves of the wall like the stairs of the pyramids created the echo of the bird sound.
And the scientific part:
Sound produces echo when reflecting from a distant surface, as we hear when shouting near a mountain or into a well. We are used to hear the same sound, with a delay correponding to the distance of the reflecting surface.
However a surprising phenomena happens if the reflecting surfaces are closer to one another - which is the case near a Mayan pyramid.
To demonstrate this we have simulated a pyramid on our PC. First, we have recorded the sound of one clap (Fig 1). It sounds like that:
If the sound is reflected from objects further apart than that, the echo will return after the clap has ended, and a "regular" echo will be heard. However, when the reflecting objects are close enough the echos overlap, and a new tone is created, corresponding to the delay between echos. For example, a 15 cm stairs spacing, will create 1 milli-second delay between echos (time it takes the sound wave to travel back and forth) creating a 1kHz tone - very different from a sound of one echo.
Then it sounds like:
You may wonder why the echo sounds like a chirp, instead of fixed tone. The answer lies in simple geometry - as the sound travels up the pyramid, the angle between the stairs and the tourist becomes shallower, and the echos further apart - reducing the tone frequency,