Sound Logic 
by Andrew Kerr

While in Metz, France last fall visiting Georgia Tech-Lorraine, I interviewed Nico DeClerq, a scientist who studies sound. The video to the right demonstrates something discussed below: clapping one's hands by this Mayan temple in Mexico creates a weird echo that resembles the sounds of one of the most sacred birds in Mayan culture: the quetzal. Is this just a coincidence, or a sign of super-smart Mayan acoustical engineering?

Q - What are you researching?

I study mechanical waves. Mechanical waves can be low frequency or high frequency. If they are high frequency it's called ultrasonics. If they are lower frequency it's called acoustics (because you can hear it).

One of the things I'm studying is the interaction of sonic periodical media. As soon as I see something periodical, I connect it to my research.

There are two interesting architectural buildings that have a periodical structure. One is the pyramid in Chichinitza in Mexico, that you can see here [DeClerq shows a model of the pyramid that is sitting on his desk]. There are four staircases, and if you're standing in front of the staircase and you clap your hands you can hear an echo that sounds different from the handclap. It's a filtered echo, and it's quite funny because the echo sounds like a chirping bird, the quetzal.

Q - And that’s the most important bird it can possibly be over there--it was venerated by the Maya. Of course, you and I both know that we cannot prove conclusively that the imitation of the bird's call was the intention of the step-builders.

A - It sounds the same, approximately, of course it's not perfectly the same, but it's good enough. The research in this case was numerical research, so I just considered an incident handclap. Then I studied how this interacted in this periodical structure given the dimensions, properties of the solids, properties of the air, just all of the physical properties that are there in Chichinitza, and the result was this quetzal echo.

Recently there are some new experiments done at this pyramid because the theory actually shows that the echo itself is determined by the incoming pulse. So if you use a handclap or a drum or another source the echo would sound slightly different. There are new experiments being done now in Mexico where you can hear a drum followed by a handclap followed by the quetzal echo or a handclap followed by the echo, and it sounds a little different. This confirms the numerical model, actually.

Q - So what are the applications of this research?

A - For acoustics this could be used for damping off sounds near highways. There's also an ultrasonic connection. Do you know what a transducer is? It's comparable to a microphone but for very high frequencies--megahertz frequencies. It transforms acoustic waves into electronic waves. Electronic fields can be transformed into ultrasonic fields, and they are filtered and so on. You could use the reverse application, too. You could use this as a detector to detect ultrasound and transform it into surface waves and detect the surface waves and transform it into an electronic wave. So this could be a new concept of transducer. One that is smaller or flatter.

Q - I read online that you were also studying a theater built in Ancient Greece.

A - In the theater in Greece there's also a filtering effect caused by the staircase, and it’s such that if a speaker is standing in the center of the theater and he speaks, then the desirable frequencies, higher than let’s say 500 Hz, are transmitted to the audience without any problem, whereas the lower frequencies are filtered out more or less. So, especially noise, low frequency sound coming from the wind and so on, is filtered out and the higher frequencies can be heard by the audience.

Q - Was this deliberately designed to produce that effect, or a lucky coincidence?

There are books that are written by the Romans that indicate that the Greeks knew about the relation between the construction of that theater and the good acoustics there. They talked about the rising sounds according to the symmetry of the theater. So there is a historical record that probably the Greeks knew about the connection between the exact seat row dimensions and the great acoustics.

Some related links:

National Geographic wrote about the quetzal phenomenon
More research on the subject of quetzals, clapping, and step pyramids
And still more quetzals, from Salon magazine
A recording of a quetzal