ASA Lay Language Papers

2nd Pan-American/Iberian Meeting on Acoustics

Pyramids and Basements



Sergio Beristain -



Popular version of paper 2pAA6

Presented Tuesday afternoon, November 16

2nd Pan-American/Iberian Meeting on Acoustics




Among Mesoamerican pre-Columbian buildings there are a series of sound effects which resemble some particular sounds that can be related to the religion or political affairs. Ancient pyramids and other structures were employed by priests and politicians as a high basement in order to make their voice heard in the distance, addressing their people, during the religious ceremonies and sometimes by the government or for social events or to promote a war or a defensive action, this was done when public address systems were not available, so it was a good media to communicate with large audiences. Sometimes directly, and sometimes taking advantage of the stone walls behind the speaker to reinforce his voice level, and of course always without grassing incidence in order to avoid sound level reduction.



Entre las edificaciones precolombinas en Mesoamérica existe una serie de efectos sonoros que simulan sonidos particulares que pueden relacionarse con eventos políticos o religiosos. Las antiguas pirámides y otras estructuras fueron empleadas por sacerdotes y políticos como bases elevadas para hacer oír su voz en la distancia, al hablar a grandes audiencias en las ceremonias religiosas o eventos políticos y sociales, o para organizar una guerra o una acción defensiva. Esto se hizo cuando no existían los sistemas de amplificación electrónica, así que esa forma constituía un excelente medio para comunicarse con mucha gente. En algunas ocasiones en forma directa, mientras que en otras, aprovechando que los muros de piedra detrás del orador, refuerzan su nivel de voz, y desde luego, siempre evitando la incidencia rasante para evitar la atenuación del nivel sonoro.



Mankind needed to develop a communications system in order to exchange information, which could be efficient and practical and which could be perceived by many people at the same time, hunting, eating and safety were probably the firsts messages they had to deal with. Among the systems developed, some were visual, like hands or body movements, but they needed continuous attention from the receivers, because if they do not see it, the message is completely lost. Somehow they found that acoustic messages were a much better signaling system option to convey human thoughts without having to stop whatever they were doing, because sound travels in all directions and can be perceived from any incoming direction too, the communication is properly conveyed even when talkers are facing each other but have something in their hands. Later they developed local languages which are complex combinations of sounds produced through the mouth, and eventually wider reach languages to communicate larger communities. In the need to get messages to longer distances, one Cesar set a chain of Towers between Gaul and Rome to send his messages. (Crocker, p. 1223).


Priests and politicians all over the world have always had the need to have one or more places where they can address as many people as possible in order to convey their political or religious messages, in the search for support, as part of a ceremony, to inform or control to the people, etc. The possibility to listen properly and understand the uttered message is of prime importance, so in the absence of any acoustical amplification system, which was the normal case from the commencement of the last century backwards, it was always necessary to find or construct a suitable place for that purpose.


In old times the only controlled sound sources available were noise generators such as whistles or drums, some acoustic musical instruments, and the human voice, neither of them have the capacity to reach very large distances and/or large audiences under normal conditions. Some recent studies have shown that some noise generators fabricated several centuries ago are able to reach a few hundred meters, but with either, no message at all, or a very simple coded message. Drums sounds could go a little further, and to code some short messages within drum beats is a simple matter. Music, although has a different purpose, has also a very limited reach, especially taking into account that some musical instruments only generate faint sounds, while others can produce very loud sounds, but this also depends on the music played. Voice is the least powerful of all those natural sound sources, its power resides in the lungs air supply, the inter-costal muscles and the larynx to create the combination of sounds (vowels and consonants) uttered, in the form of words and sentences, to produce full sets of information, which can be used for very many purposes.


When someone speaks to a group of people located at the same height as him, his voice is easily understood only a few meters away, because the audience, their clothing and the furniture absorb a lot of his voice energy, so the audience he can address is relatively small, without having to increase his voice level, or even shouting.


Anyone located above the audience, can be easily and clearly heard up to a much longer distance, allowing speech understanding by more people. First, his physical position may call for attention from the audience, and if it is complemented by any rank position he may bear, as for the dressing, companionship and/or expected communication. Religious as well as governmental authorities are always expected to present speech communications in any kind of ritual, political or community gatherings, this is why it is very common to find altars, pulpits and templates installed in many public plazas, theatres and temples.


All the archaeological sites found and studied in Mesoamerica have sets of high and small pyramids and stone basements, plus some little buildings which might have been used for the commanding people living, many of those high constructions are located in front of very large flat open areas, where many people can be accommodated in order to listen to whatever sounds might be presented from the top of these places. Those pyramids and many of those basements were frequently employed for ritual and/or political purposes as can be seen in Figure 1 (lost-civilizations), which depicts a high Aztec pyramid with a tall temple on top of it, which was located where nowadays is the very center of Mexico City down town, with two small basements by the sides of the pyramid, and plenty of people gathered in the large flat area before the pyramid.


The archaeologists suggest that these kind of gatherings were fairly common in ancient times, and as it can be seen in the figure, most of the people is organized in two large groups forming a wide central corridor where some important people is approaching to the base of the pyramid, probably to start a ceremony of some kind, and/or convey spoken messages useful or interesting to the people gathered there. At the top of the very long stair ways, few people can be seen commanding the meeting. The longer distance of the flat area for the audience is in front of the façade of the pyramid.




Figure 1. Aztec pyramid and a large people gathering before it, two little basements and a few other buildings.


Speech messages

Speech sounds are produced and conveyed by the sound waves that are created by the breath stream as it is exhaled from the lungs by the pressure from the chest and diaphragm muscles, and further modified by all the so called speech organs, actually the voice mechanism of the human body only has the vocal cords to produce speech sounds, the rest of the system is originally itended for breathing and eating purposes, which are vital needs. These speech organs start with the vocal cords in the larynx, which by opening and closing the air passage, produce a very rich tonal sound with a fundamental tone around 100 Hz, and plenty of harmonics; the pharynx conduct to the mouth with its hard and soft surfaces and the cavity, which provides the basic timbre of each person; the mouth and the nasal cavities supporting the same process of timber generation; and the tongue, the teeth and the velum, which are in charge of the articulation of the speech vowels and consonants, by complementing the vocal cord sounds with fricative and impulsive sounds (Sanders p. 173).


Normal average human voice level is known to be around 65 dB (A) at 1 m. from the speaker mouth, that is when people have an average conversation, or address a small amount of people in a little room, which corresponds to a few μWatts (Harris, p.16.2). Sometimes the speaker is required to increase his voice level in order to be properly heard and understood over a larger distance, many people can easily do it, although not everybody can do that without some or a great effort, generating sound pressure levels in the vicinity of 90 dB (A), for a total emitted power around 1 mWatt. The human voice does not produce a constant sound level because some letters and syllables have more energy than others (for instance an f, an a or a k). These level fluctuations while speaking are expressed as the dynamic range of the spoken sounds, and are represented by the difference in dB of the maximum and the minimum sound levels along several sentences (including many different letters). This range has little dependence on the average speech level, whether it is a whisper, a normal talk or a shout, and fall within 30 and 40 dB.


Figure 2 below shows the relationships between speech level, noise level and distance for good understanding of speech sounds. (Sanders, p. 182). For lower noise level and higher speech level, the message can be received properly at a longer distance.




Figure 2


The average frequency range for spoken sounds falls between 100 Hz and 8 kHz, but some men can produce frequencies as low as 85 Hz with vocal sounds, while for most women the lower frequency usually is over 150 Hz, and some sibilant consonant sounds from some speakers can go as far high as 10 kHz. The emitted sound power is not evenly distributed along the frequency range; more sound power is present in the low frequency side of the range than in the high frequencies.




Figure 2. Usefulness of speech messages over the distance in the presence of noise, according to the voice level. As can be seen, the lower the noise level, the longer the distance where a message can be fully understood.


Most of the energy of the speech sounds go in the direction straight in front from of the speaker mouth, within a solid angle of some 90 degrees, and much less energy goes in all the other directions, anyway, his voice can be heard and understood even behind the speaker, only that the useful distance to get the full message correctly understood is much shorter than in front of the speaker.


With these three simple sounds, words and sentences are formed with varying combinations of vowels and consonants. Vowels are harmonic sounds generated in the glottis (vocal folds), and slightly modified along the vocal tract to produce over 15 distinct known vocal sounds, although Spanish only uses 5. Figure 3 depicts a time graph of a word and the frequency spectrum of an ‘a’ as in ‘bat’ at a fundamental frequency of 100 Hz, and can be seen that it includes over 25 harmonics within 14 dB, some voices can have more than 40 harmonics. Consonants can be vocalized or not, but generally speaking, have less power than vocals, especially the non vocalized ones, but carry most of the message comprehension information (Sanders, p. 176). Consonants might be harmonic or not, for instance a t or a p are impulsive with a wide continuous spectra, a b is a sort of blow with some vocal support sound, so it produces a wide spectra and some clear tones, most of them are fainter than vocals, but carry most of the meaning of the speech.


In order to make some messages more easy to understand, fewer words (i,e. smaller or limited vocabulary) can be employed to structure the messages, so when somebody misunderstands one or more words, he can judge if the perceived one could or could not have been uttered in the middle of the other words that he actually understood (Sanders, p. 183), this is also helpful with large sentences in normal speech. Other way to guaranty easy understanding under harsh conditions is the use of so-called coded messages, as in the case of saying positive or negative instead of yes or no. This way of talking works well under any circumstance, but it is even better when speakers and listeners are aware of it.




Figure 3. Time response of the ‘example’ word, and frequency spectrum of an ‘a’ as in ‘bat’, showing over 25 harmonics accompanying the 100 Hz fundamental frequency.


Intelligibility of Speech

Intelligibility of speech is the term employed to specify the quality of a speech communication system in order to determine the possibility for an audience to understand a spoken signal and it is based on the analysis of different acoustical conditions. It can be estimated from several parameters developed by several researchers for this purpose, like the Articulation Index AI; the Preferred-Octave Speech Interference Level PSIL; the Preferred Noise Criteria PNC curves; the Speech to Noise ratio in dB (A); or the amount of time that the reverberation lasts in the place where any speech message will be presented to an audience. (Sanders p. 182).The communication system could direct (acoustical), or through electronic equipment (Electroacoustic).


AI is a easy but elaborate calculation that first requires some noise and speech level measurements in 1/3 octave bands, then the extraction of the level difference in each band, and the application of a different weighting values, according to its contribution to the understanding of the message, to each and every 1/3 octave band speech to noise difference in the range from 200 Hz to 4 kHz, before adding up all the individual resulting values in order to get a final value which will be between 0 and 1. Where 0 means no possibility at all to understand a word, while 1 represents the possibility to understand the whole message, but actually the real intelligibility of the spoken message is highly dependent on the message itself, the vocabulary employed, and the context of the message. Sentences of a known topic will approach 100 percent intelligibility with an AI of only 0.4, while simple words out of context require a larger value, so bellow 0.3 is considered as unacceptable, 0.3 to 0.5 as acceptable, 0.5 to 0.7 as good, and beyond that as excellent.


PSIL was developed as a simplified method to evaluate the same problem of intelligibility of speech in the presence of wide band noise, and it is determined by the arithmetic average of the octave noise levels at 500 Hz, 1 kHz and 2 kHz, which are considered the most important frequency bands for the intelligibility of speech, and then compared with the speech level. For instance, at normal voice level of 65 dB (A), a PSIL of 60 is considered satisfactory, i.e. only 5 dB bellow the normal speech level.


The Preferred Noise Criteria curves developed as reference noise levels that could be acceptable for many acoustical installations, represent sets of curves from 63 Hz to 8 kHz in octave bands, which should not be exceeded by the noise level according to the application given to different places or acoustic signals involved, as for instance in any sitting area of an auditorium, the noise level should be bellow the curve PNC 35 in order to allow full understanding of the spoken messages.


Another way to estimate the speech comprehension is by measuring the amount of acoustic noise present in the environment while talking and the speech level in dB (A). This parameter is commonly expressed in the Speech/Noise ratio (S/N), and it is represented by the dB difference between the speech and the noise sound levels. It is always desirable to be able to provide a positive and large S/N ratio, i.e. the voice level well over the noise level, and when this value is 15 dB or more, the voice message passes without any acoustical disturbance and then it is easily and completely understood, while S/N values in the range of 7 – 11 dB are good enough for most people to understand the full message. When the S/N value is further reduced, still the message can be fully understood, although the lower the value, it requires from little to a lot of attention and discipline from the audience side, and then the S/N could be as low as -10 dB (Harris, p. 16.6).


This means that if for instance, when the background noise level is in the order of 30 dB (A), which is a background noise level easily found in the open space without the presence of nowadays machinery, mechanical ground and air transportation and electronically amplified noises, normal speech can be very easily understood up to some 16 m. away from the speaker, because the speech level will be in the order of 41 dB, i.e. an Speech/Noise ratio of 11 dB. Some speakers can produce higher level voices, as high as 82 dB (A) without great effort for them (shouting they can reach some 88 dB (A)), which means that they can produce a S/N ratio of around 17 dB better than the average speaker, further increasing that distance, under the same general acoustical conditions, to a little more than 120 m., where the speech level will be in the order of 40 dB, provided there is not extra attenuation over the square distance law for the sound level, which indicates that the sound level is attenuated by 6 dB per doubling the distance from the sound source (Rossing, p. 115).


The ear capacity for level and frequency is very large. It can detect sound levels from 0 up to 120 dB, representing the range from 20 μPa to 20 Pa of acoustic pressure, and frequencies from 20 Hz to 20 kHz, making nearly a ten octave range with the higher frequency 1000 times larger than the lower, which means that all the speech sounds in level and frequency are located in the very central part of these two extremely wide ranges, where the discrimination of sounds is much better than near the edges, Figure 4 shows the normal speech range in the central area of the ear capacity (Beyer, p. 109). This can be explained because speech was developed after the ear, people is borne with their full hearing capacity, but need to learn to speak, so groups of people formed their communication languages with sounds they could easily generate, and also were easy to discriminate from other sounds in order to avoid confusion. This also explains why there are very many languages in the whole world.


Reverberation time, represented by the length of time that the ear can still listen to and integrate to the original sound from the source, the sound reflections produced inside any room, and arriving to the ear with very short time delays. For proper intelligibility of speech within rooms, reverberation times from 0.4 to 1 second are appropriate, depending on the room size, and in general the shorter, the better. This is the main parameter that prevents understanding of speech sounds, for example, inside many churches, where reverberation times in the order of 2 to 5 seconds are common place.




Figure 4. Amplitude and frequency ranges of speech (dashed area), and hearing capabilities (between feeling and audition thresholds) of human beings.


Together with the S/N ratio, the meaning of the speech sounds, the context of the heard sentences and the topic being presented to the audience have a great influence in the possibility to understand the uttered message, for instance, in the presence of the same amount of noise (i.e. the same S/N ratio), when people have some knowledge of the presented topic, or it is within an already known context, they will be able to understand a lot more than when they are totally unfamiliar with it. This is the main reason to use an especial small set of words when understanding of the message is paramount (Sanders, p. 178), for example as in airplane to ground communications.


Directivity is another issue which can also drastically affect the intelligibility of speech, because as already mentioned, most of the voice energy goes away from the speaker directly in front of him within an angle of some 30 – 45 degrees at each side of the central axis, which is also dependent on the radiated frequencies (wider for low frequencies and narrower for high ones), and then usually the speaker moves his head continuously while talking, looking at different areas of his audience, and momentarily neglecting others, especially at the edges of the audience area.


In an open space, like in front of a Pyramid or a tall basement, some 15,000 to 20,000 standing people can be comfortably accommodated within a floor area of 100 x 100 mts., where the farthest person would be located at just little over 110 m. away from the speaker, considering him to be within at an angle of 30 degrees to either side from the main axis of the speaker voice radiation, so this is a kind of a crowd that a single person can address without the use of electronic amplification, provided there are no obstacles or intruding noise. And for music and drums shows, the distance and addressed audience could be a little larger, especially when supported by visual displays as dances or ritual activities, which were rather common in ceremonial sites.


By the times when pyramids and basements were built and frequently used, the main source of noise could have been the crowd itself and some other natural sounds such as wind, waterfalls and animals (there were no traffic or industrial noise).

Experience has proven that  most of the audience in the very last rows of large gatherings, as far as they could be very interested in the message, they also know that it will be difficult to understand everything that is spoken far away from him, especially with a crowd in the middle of the way.


The last element for a good communication system is the listener itself who can have advantages and disadvantages such as: 1. Familiarity with the kind or topic of message; 2. Known general vocabulary; 3. Interest he might have on the topic; 4. Attention given to the speaker; 5. Concentration he may set to try to understand the message, especially in difficult acoustical conditions; and 6. Good hearing capacity in both ears. So even a well uttered message, under excellent acoustical conditions and low background noise level will not be fully understood by the audience if the listeners lack one or more of the above mentioned and bellow described parameters.


1. Familiarity is related to the previous knowledge by the listener on the general topic being presented, which helps him to build up inside his head the small parts of the message that might disappear due to head movement of the speaker, a lack of articulation from the speaker, some short sudden noises, etc.


2. People who handle a larger vocabulary than others will understand more of a given message because it will be simpler for them to discriminate between similar words. Conversely, when the speaker uses a simplified vocabulary, and it is known by the audience, it will be much more simple to understand him.


3. Interest in the message is the real desire to get informed and/or updated in the topic presented. Interest promotes attention.


4. Attention is the willingness to listen to and to understand what is being presented. The message is easily lost if the audience is paying attention to something else.


5. Concentration allows people to fully understand spoken messages within harsh acoustical conditions, like in the middle of a party or in the within a crowd that has less interest in the same message.


6. People with limited hearing capacity due to some sort of sickness or direct damage to the ear will need much better acoustical conditions and louder voices in order to properly understand messages. This problem is highly dependent on the amount of hearing loss and the frequencies actually affected.


Atmospheric effects

In open spaces, there are several atmospheric phenomena that might affect the propagation of sound, increasing or decreasing the sound propagation speed, add some extra voice level attenuation, or even by filling some areas with sound that otherwise will not receive enough. Among the main aspects are the effects of soil, due to its porosity, and that of the audience, both of them can introduce attenuation and delays, due to friction and thermal variations; the wind and the air temperature (Rossing, p. 114). These factors could reduce the sound level by some 15 dB more than the square low states, but usually it is actually more noticed beyond 100 m. from the sound source, which means that some of these effects are usually small within the expected distance.


There could also be interference by the same signal, which could be either, constructive or destructive, due to reflection from soil or walls, with changes in amplitude and phase. In general nearby wall help to increase the average voice level, a single stone wall located a short distance behind the speaker, will increase his sound level by some 2 – 3 dB. Instead, distant walls may produce echoes that could disturb the message.

Although actual attenuation frequently sticks to the square law process only within the mentioned distance, with some little gaining’s by reflection on nearby hard surfaces, and sometimes with the help of the environmental conditions such as wind and temperature gradient, all together will allow for a convenient communication, provided there are low environmental and crowd noises.


Beyond some 100 - 150 m. understanding is more dependent on the atmospheric conditions, which can help to improve it, or further deteriorate the message.


Addressing the people

When a priest or governor of a given culture had to stand on top of a pyramid or a high basement in order to utter a message to his people, most of them had to pay attention, because there was no way to increase the voice level beyond the natural capacity of the speaker, plus the acoustic conditions of the site.


Speech intelligibility is dependent on the speech level, and the noise level (Rossing, p. 311). So the main reason for not understanding by the audience was that the very crowd was not willing to be quiet enough while the speaker sent his message.


In some rituals, many people are not so much interested in the message itself, word by word, as they are in the significance of the rite itself, so in many cases, understanding each and every word was not absolutely crucial.


Most of the Mexican and American pyramids were employed as ceremonial sites, where people used to join to celebrate many different festivities, but also to receive information from the higher ranked people, messages about war situations, community safety, agricultural activities, religious rites, etc., that is why it can be assumed that the crowd used to pay attention to the speakers while in front of the pyramid or basement.


Level, distance and perception

The sole attenuation by distance according to the square of distance law is in the order of 6 dB per doubling the distance, so as explained before; a reasonable voice level can reach the audience in the lower flat bellow the basement. When one or more stone surfaces reflect the speaker voice within a few milliseconds (i.e. a few meters away from the speaker), an increase of 3 to 5 dB can be easily obtained, and clarity is also reinforced by these few first reflections, conveying the voice message to a larger distance from the speaker. With the use of other sound sources as implemented by antique groups, the event could have been noticed up to well beyond half a kilometer, for example with some single studied noise sources from those times, which generate 95 – 98 dB at 1 m. they can be heard well above the background noise that far away.

This also explains why church or public buildings, bell towers, carillons, sirens, people conveying voice messages and other sound systems are frequently located in high positions as towers, hills, etc.


The Ball game court in Chichen-Itza is an example where normal level voice can be easily understood over a very long distance, in the basements of this court located one before the other, across the longer axis of the court, because it is supported by several hard surfaces reflections in soil and walls, as well as free of obstacles between source and listener.


Every space has its unique sound, which depends on size, materials, form, which affect reflection, dispersion, absorption, refraction, etc. (Blesser, Salter, p. 12), all the mentioned factors, plus the activity and the attention given will influence, the level, the perception, and understanding of the emitted sounds in those spaces.


Some measurements


Figure 5 presents a drawing of a basement similar to the one measured for the preparation of this paper, except for the construction located above it. (lost-civilizations),




Figure 5. A basement similar to the one studied. The main difference is there were no extra buildings on top of it.


The basement is a flat surface 2.3 m. high over the flat area for the crowd, with 14 steps to get on top of it, so the speaker mouth would be about 3.8 m. above the ground level. Many sound level measurements in octave bands and in dB (A) were performed in the top of the basement, and on the flat hard floor area in front of the basement, which is an open space, with no less than 60 m. before any obstacle could be found. There was no wind present at the time of the measurements, and the temperature was also stable by mid-day.


A pink noise sound source was located near the edge of the floor on top of the basement, and the first measuring point was chosen at 1 m. just in front of the source, in the radiation axis, to set a reference level.


Table 1 presents a few measurements of sound pressure level from the sound source location (1), which was emitting wide band pink noise with frequency response according to the speaker system used, it also shows the sound levels at three points at an angle of 30 degrees from the radiation axis, points 2 through 4, and distances of 10, 20 and 40 m. away from the sound source. Measured values on axis are also shown in points 5 and 6 located 10 and 40 m. away from the sound source, for comparison. Background noise level in octave bands and dB (A) is also shown in the last row if the table.


Table 1








dB (A)

















































Background Noise









The above Table only shows a selection of the measurements. 1 Sound source at 1 m., in the radiation axis, 2, 3, 4 at 30 degrees from the radiation axis, and at 10, 20 and 40 m. from the sound source. Points 5 and 6 show values measured at 10 and 40 m. on axis. Figures rounded to the nearest full dB value.


Figure 6 bellow shows a profile of these measurements locations. All measurements were performed at 1.5 m. above ground level, which is the measuring height recommended by most noise measurement standards.




Figure 6. Showing (not in scale) the basement, plus the sound source and some of the measuring points locations.


Results or comments

Measurements were performed without a crowd, so measured values indicate only the direct sound attenuation which proved to be as expected by the square distance law, but with a real crowd, there would be a little extra attenuation by people heads, and it would be noticeable special by the point 4 area and beyond, due to almost grassing incidence at that distance from such a low height basement, areas around points 2 and 3 will not be affected at all by this condition because they receive the direct sound from the sound source without any obstacles from a bigger angle. Even with the expected limitations by the presence of the audience, the voice uttered from the top of the basement will be easily understood in the studied area, and ceremonial rites would be clearly appreciated by anyone standing in the flat area bellow the basement.


The higher the basement, as for example from the top of a pyramid, the spoken sounds will clearly reach to a larger distance and a larger audience also, because the sound will be perceived by all the crowd in the distance from a bigger angle than in this case, thus reaching the crowd completely free from any obstacles, directly from the sound source to the audience, and then the sound level reduction will only be affected by the square distance law.


According to the articulation index definition (AI) and considering the background noise actually measured, although only in octave bands, taking these values as if they were 1/3 octave ones, which gives some extra safety margin in the results, plus the estimated voice level at the longest distance of 60 m. in the studied plaza before the basement, the AI could easily each a value in the vicinity of 0.83, which is actually considered as excellent.

With regard to the preferred speech interference level PSIL approach, with the octave noise level measured at the three frequency bands from 500 to 2000 Hz, a PSIL of 20 dB is obtained and it is considered very quiet, meaning that a loud voice uttered in the studied conditions can be easily understood in the mentioned area. It can be concluded that the higher the platform, the longer the useful distance, up to a practical maximum of some 120 m. due to the effects of atmospheric conditions above explained, and noise.


Intelligibility over longer distances can only be achieved with the support of some strong reflections from nearby large walls, as in the case of the Chichen-Itza Ball game. The walls have to be near in order to avoid echo formation, or sound could be amplified as it is done nowadays, with the help of electronic amplification.


The octave band background noise measured corresponds to PNC curve of 20 dB, which is considered as very good for large auditoriums, theatres and churches in order to allow for full intelligibility of speech (Sanders, p. 187). This means that the only noise that could have easily affected the speech intelligibility in the studied site, would have been the one produced by the crowd itself.


With regard to the Signal to Noise ratio approach to the speech intelligibility, it also confirms full understanding of messages within the distance studied and atmospheric conditions and noise present during the measurements.


Reverberation in this case is not an issue because it is an open space where reverberation is not produced.


All the main pyramids, and many of the small ones, in the ceremonial sites in Mesoamerica are much taller than this studied basement. Confirmation of the above statements has been obtained by the author without any test equipment in several archaeological sites. Further research will be performed in several other basements and pyramids, together with other acoustical studies, in order to complement this one.



Pyramids and basements can be conveniently used for speech messages, and probably it was in the past a common use of these constructions.


Speech communications might not have been the main reason to build pyramids or basements, as rituals and other festivities could be the first purpose, but definitely they can be used to convey voice messages.


Nowadays, some of these kinds of sites are employed from time to time to represent dances, theatrical plays or musical performances to very large gatherings, making good opportunities for people to get to know this interesting heritage.




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