In Part 3 of Architecturally Sound, learn about chirped echoes and colouration, acoustic phenomena found at the ancient Maya Temple Kukulkan.
Watch my video for a demonstration of chirped echoes at Supawood's HQ.
Interesting Fact: You may not realise, it is 0°C on the day that this video was recorded. This is interesting as the speed of sound is directly impacted by temperature. On cold days, sound actually travels slower through air than it would on a hot day. This is due to the molecules in the air moving slower as a result of reduction in heat. Sound at 0°C travels 12m/s slower than at 20°C!
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Case Study: Temple of Kukulkan (El Castillo Pyramid)
Situated in Chichen Itza, Mexico, beholds the Kukulkan Temple. It is a Mayan step pyramid with wide staircases consisting of 91 steps. Kukulkan is the Mesoamerican name for "feathered serpent", in reference to the Mayan god of the same name. An amazing acoustic phenomena can be heard from the staircases. The result is an auditory experience that appears as magical or otherworldly.
When positioned in line with the staircase, an observer claps their hands. The sound interacts with the pyramid and then returns an unexpected 'chirp' that drops in frequency.
The 'chirp' appears to mimic a local bird, the Resplendent Quetzal. (If you are wondering, Quetzal is pronounced 'ket-zal'.) When also positioned parallel to a distant hard surfaced flat stone wall, a singular 'snap' echo can be heard after the chirp. The 'snap' sound mirrors a snake's tail rattle, thereby completing the effect of the astonishing feathered serpent!
Studies by David Lubman   , indicate that it is highly likely that the design and the acoustical outcome is intentional. David Lubman suggests that  a priest could clap his hands at the pyramid steps and interpret the return sound from Kukulkan to the followers. As with the Great Ballcourt (see Architecturally Sound: Part 2 – How Flutter Echo Impacts a Space), "mind manipulation" could be achieved through the resemblance to the likely sound made by the powerful Mayan god Kukulkan.
How does it work?
The design parameters of the staircase, location of the source and the hand clap itself all are required to create the effect. It is likely that the design parameters are relative to the target wavelength. The positioning of the observer will also create varying auditory responses depending on the distance to the staircase. As the distance of the observer increases, as will the angle of incidence to many of the steps, thereby altering the parameters (relative to the observer) and thus the sound of the chirp.  David Lubman reports "The further you stand the lesser the frequency range.”
Varying degrees of scattering (non-specular reflection), diffraction (bending of sound waves) and focussing from junctions are occurring to create this amazing effect! The outcome is a long delayed echo that contains an emphasis of certain frequencies over others. This is defined in acoustics as colouration. This is bad when conducting acoustic design for speech and can cause poor levels of acoustic comfort. Although colouration in everyday architecture is not usually defined by long delayed chirps, it holds a significant influence on speech intelligibility in room acoustics.
“Colouration, in most acoustic environments, is an unwanted distortion that interferes with the function of the space.” says Osborn Fong, an engineer from Acoustic Directions. “For example, large rooms that have insufficient acoustic treatment to control the low-to-mid frequency range create an imbalanced reverberant environment that degrades speech communication, as the lower-frequency sounds from lingering earlier words conceal the higher sounding consonants of subsequent words (this phenomenon is commonly known as the upward spread of masking). Unwanted colouration such as this can be adequately addressed in most cases by incorporating amounts of carefully selected frequency-targeted absorption in the room.”
Simply, colouration in room acoustics changes the frequency response of a sound. This could be a spoken voice, instrument or sound from an audio system. Multiple uncontrolled room reflections are the cause, and this will lead to poor acoustic comfort. It takes detailed analysis and calculations to determine the acoustical requirements of a room.
Absorption and diffusion can be used to control colouration. Both can be used effectively depending on the requirements of the room. Good acoustic products with quality acoustical data is required. A particular focus on the frequency spectrum of acoustic panels is required. This ensures that the correct frequencies are being absorbed according to the acoustic calculations.
The below image is an example of reliable acoustic data on a good acoustic absorber. It displays that it is NATA Certified, tested in accordance with AS ISO 354-2006 and also provides a link to the full lab report.
In some instances, hybrid surfaces providing absorption and diffusion can be used.
Hybrid acoustic panels providing both absorption and diffusion - Acoustic Consultants - Chris Field, Keith Hewitt
Most rooms are unique. Each will have its own frequency response and reverberation time. Sums of the characteristics of the room's function, surfaces and dimensions will all result in a differing interaction of metrics. This takes time and a detailed analysis.
There is no one size fits all acoustic treatment. Getting the highest NRC product will not solve your acoustic issues.
There are many other complicated factors that are involved, so remember to speak with your acoustic consultant when designing any room for communication.
Part 1 - Why Acoustics Matter In Great Architecture? Go here to read it now>>>
Part 2 - How Flutter Echo Impacts a Space. Go here to read it now>>>
 David Lubman, Convolution-scattering model for staircase echoes at the temple of Kukulkan Acoustics '08 Paris June 29-July 4, 2008
 David Lubman, 79th Meeting of Society for American Archaeology, April, 2014, Austin, TX
 David Lubman, Archaeological acoustic study of chirped echo from the Mayan pyramid at Chichen Itza, in the Yucatan Region of Mexico ... Is this the world's oldest known sound recording?, October 13, 1998 136th ASA Meeting, Norfolk, VA
 David Lubman, Acoustical features of two Mayan monuments at Chichen Itza: Accident or design? The Journal of the Acoustical Society of America 112, 2285 (2002)
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