[Aztlan] Voice of the quetzal

[David Lubman]

Jorge:

Thanks for your perceptive comments and challenges.

The discussion (was it an argument?) did indeed take place some years ago on 
the old Aztlan. It's not uncommon to revisit subjects. That's why our 
activities are called "re-search". It is also appropriate when scientific 
paradigms have changed, which is the case here. It is appropriate, too, when 
new evidence comes into play, which is also true.

I respond to your points in the same order you offered them.

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1    "There are far too many things that are different now from the original 
conditions of the building and city. The first thing that comes to mind is 
that the current shape of the building is very much a result of the 
reconstruction work of XX Century archaeologists."

The chirp phenomenon is caused by the staircase, not the building (pyramid). 
Examination of the echo sonogram shows little influence of the building. 
Chirp parameters are predictable from staircase design and the positions of 
observers alone, with absolutely no consideration of the building. This is 
because the angled pyramid surfaces reflect sound upward, away from the 
observers. Only a small amount of scattered sound is returned.

I have little knowledge of the shape of the unreconstructed building. My 
recollections of a single pre-renovation photograph was of a possibly 
pyramidal mound of dirt with trees and brush growing from its sides. I will 
be grateful if you would share that information with me.

-----------------
2    "Secondly, the plaza would have been paved with hard stucco, which 
would radically alter the sound features of the place."

I don't agree in this case. I judge that the presence of a hard stucco 
pavement instead of the present tamped and grassy earth would interfere with 
the echo only modestly, for the following reasons.

True that a hard pavement would likely be highly sound reflective. True that 
sound reflected and scattered from pavement would also scatter sound toward 
the temple and back to the observer. But please note that to a considerable 
extent the same conditions exist now. Yet echoes and sonograms show little 
or no ground effect. True that the present grassy earth is not as hard and 
therefore not as sound reflective as the former pavement. But the present 
ground is somewhat hardened from daily tamping by the feet of thousands of 
visitors. And yet the chirped echo by far dominates the sonogram. Ground 
reflections would need to increase by tens of decibels to obliterate the 
prominent chirp feature. Moreover, in ancient times the space between the 
observer/clapper and the pyramid probably contained many people (as one 
might expect on ceremonial days). That would greatly attenuate sound 
reflected from the pavement.

Recognize that this is a testable hypothesis. Computer simulation and field 
tests can show the effects of soft or hard ground or no ground on the echo. 
The science of architectural acoustics is "hard" enough that you need not 
accept even expert opinions.
-----------------
3    The building itself would have been covered with stucco and perhaps 
even other materials.

As discussed in (1), the building has little effect on the echo phenomenon. 
(Sonograms do show evidence of relatively weak echoes from the building. 
Echoes are weak because tilted pyramid surfaces reflect sound upward at high 
angles rather than back to the observer/clapper)
-----------------
4    And is there any evidence that anyone in the city's heyday would have 
gone around clapping his/her hands to get sound effects from buildings?

I have only weak anecdotal evidence. The father of Mexican man raised in 
Guadalajara advised that should he ever ascend the pyramid of his ancestors 
he should clap first to show respect. In some other cultures clapping can be 
a request for attention. This question might more fruitfully put to an 
ethnographer.
-----------------
To terminate this lengthy post I will withhold evidence mentioned in my 
first paragraph.

Thanks again, Jorge, for your thoughtful attention.

Best regards,

David Lubman
-------------------

----- Original Message ----- 
From: "Jorge Pérez de Lara" <jorgepl at estudioelias.com>
To: "Aztlan" <aztlan at lists.famsi.org>
Sent: Monday, January 01, 2007 12:05 PM
Subject: [Aztlan] Voice of the quetzal

SNIP!