An Archeoacoustic Look at Two Hindu Temples

Much of the research into the historical acoustics of worship spaces has focused on Christian churches or Islamic mosques. However, little is known about the acoustic history of Hindu worship spaces, despite Hinduism being the third largest religion in the world. Shashank Aswathanarayana and Braxton Boren (American University) share their efforts to fill this knowledge gap by studying the acoustics in Hindu temples from the 8th and 15th centuries. 

Associated paper: Shashank Aswathanarayana and Braxton Boren. "Acoustic analysis of two Hindu temples in Southern India." JASA Express Letters  5, 031601 (2025). https://doi.org/10.1121/10.0036033.

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 Music: Min 2019 by minwbu from Pixabay. 

Transcript

ASA Publications (00:27)

Today we're talking to the authors of an article that was featured on the cover of the March issue of JASA Express Letters, “Acoustic Analysis of Two Hindu Temples in Southern India.” With me are Shashank Aswathanarayana and Braxton Boren. Thank you for joining me. How are you?

Shashank Aswathanarayana (00:41)

Doing good.

Braxton Boren (00:43)

Doing well. Thanks for having us.

ASA Publications (00:44)

Great. So first tell us a bit about your research backgrounds.

Shashank Aswathanarayana (00:48)

Okay, yeah, so my research and my personal story are actually closely intertwined. I have learned Indian classical music since the age of 10, and that has had a deep impact into the research questions I delve into. Trying to, you know, my work is driven by questions of applicability and transformation of musical experiences.

In terms of my educational background, I have an undergrad degree in electronics and communication engineering, followed by a master's in music technology, and a PhD in media arts and technology.

ASA Publications (01:24)

Very cool.

Braxton Boren (01:25)

Yeah, similar for me. I  had multiple interests. I was a classically trained musician, but studied acoustics and physics. And also, my father was a high school history teacher, so he, I think, inculcated a love of very old things into me. So whenever possible, I like going to very old spaces and thinking about how their sound has changed over time.

ASA Publications (01:48)

And now we get to talk about some very old spaces and their sound. To start, how do acoustics play into the architectural design of worship spaces?

Braxton Boren (01:56)

Yeah, I mean it's a  big question in general. We know that acoustics are very important all performance spaces, including worship spaces. It's sort of an open question how much acoustics is the first order design principle in some of these historical spaces, and even today, lot of spaces, architects will tell you that they don't think about acoustics that much when they're starting off, to the frustration of acousticians, of course.

But I think also this is some of the power of the auditory sense, that the auditory sense is in the background, so it's working sort of as our backdoor sense, you know, to let us know something's behind us, you know. It's like a film score, it's working on the background, and it affects you in ways even if you couldn't tell at the moment that it's the film score acting on you. So a lot of these spaces will have, you know, a very unique soundscape that really drastically affects someone's experience of it, but it may not have been, you know, the first reason that someone designed the space was mainly for the soundscape, but it is something that is directly sort of connected to it.

ASA Publications (02:56)

That makes a lot of sense. So what role does sound play in Hindu worship?

Shashank Aswathanarayana (03:00)

So this is a very loaded question and within Hindu worship, it’s got many layers to it. To begin with, I’ll talk about the Vedic period. This is from about 3000BC to about 1st century CE. There is debate over the exact time period, but this is a broad range. This is the period pre-temple construction and idol worship. So in this period, basically religious life centered around the Yajna or ritual sacrifice. Now the two central features of this Vedic ritual were the sacrificial fire and the oral recitation of the Vedic mantras. Now mantras were recited to invoke God, and offerings were given to God in the sacrificial fire while mantras were chanted. And around 1000 BC or so, still in the Vedic period, whilst the mantras were still the central components of worship, the notion of sacred sound emerged in Hindu traditions and the scriptures called the Upanishads. These texts spoke about the syllable “Om” as being the Supreme Absolute Sound or the Śabda-Brahman. Through all this, it is very evident, that sound played a central, important role right from the earliest roots of the religious tradition.  

Now, over the course of the last 4 or 5 millennia, the type of worship has evolved from the Vedic period to now what is known as the post-Vedic period. The post-Vedic period is marked by the emergence of idol worship and the construction of temples. This resulted in a change in the type of worship and consequently the evolution in the sound component as well. It evolved from the Supreme Absolute to the earliest classical music, called Gandharva Sangita, to bhakti or devotional Sangita. Now Sangita means music; it’s just a literal translation. Ritual worship in the present day uses a combination of the recitation of the Vedas and other Sanskrit scriptures, sounding of the bell, the conch-shell, as well as music. All of which is to say that sound has played and continues to play a critical role in Hindu worship. 

ASA Publications (05:23)

Okay, okay. So it makes sense in theory that the worship spaces would be designed with that in mind. So why are you interested in historical temple design?

Shashank Aswathanarayana (05:34)

Well, as I said earlier, I'm a musician growing up listening to songs that were sung in praise of the various gods. I became curious to understand how the temple itself might have impacted the music. And as I began delving into this question, I realized that there's not much research that's happened in Hindu worship spaces. And being the third largest religion, accounting for about 16 % of the world's population, I felt this was a large gap in the field, and I became more drawn into it try and find some answers.

ASA Publications (06:08)

That's awesome. Okay. So what was your goal in this work?

Shashank Aswathanarayana (06:12)

Well, to put it very simply, to understand the acoustics of two iconic temples in southern India. You know, we, as Braxton and I started thinking about this question, we were like, okay, you know, there's not much work done. Where do we start? And the first thing that came to our mind was we should probably find temples which have musical connection to them. And that’s how we started with these two freestanding temples in southern India. Braxton, do want to add something?

Braxton Boren (06:42)

Yeah, I mean it's always exciting when you have sort of a white space, you know. So I've done a lot of work with historical, especially church design, a lot of sort of old European churches that I've looked at. And Shashank was interested in this work, but he was interested in it obviously from a Hindu perspective, so trying to apply some of the techniques that we may have applied to European churches and then trying to see does that fit necessarily with Hindu temples. And there's a very standard way that you think about these things in the context of Christian churches. For instance, they have a sermon, they have sort of a conflict between speech intelligibility and musical reinforcement. So you have longer reverberation, it might be better for music, it might be worse for the sermon, and there are all kinds of historical conflicts over this during the Protestant Reformation and other periods. Whereas in Hinduism, it's just a very different service and there’s not sort of a long sermon where someone gets up and talks to you for half an hour, so you don't have necessarily the same trade-offs that you might in the context of Western worship space acoustics. So, yeah, we're trying to think about, generally, that this is a completely different field. Are there ways in which we need to think about the problem differently based on the context of Hindu worship?

ASA Publications (08:00)

Okay, okay, very cool. That is an interesting question. So tell us about the two temples you looked at.

Shashank Aswathanarayana (08:06)

Yeah, so both of the temples that we looked at are actually UNESCO sites, so culturally very important. The first one is called the Virupaksha temple. It's in a small town called Pattadakal. It's an eighth century temple. And this temple is built of red sandstone. And one of the reasons we chose this was this temple is part of the complex which is perhaps one of the oldest freestanding complexes in the country. And additionally, there are inscriptions found in the outer wall which talk about donations made by the queen of the area to the temple musicians. 

And the second temple is called the Vijaya Vittala temple. And this one is a 15th century temple. It’s in the same state of Karnataka. It's in a town called Hampi. It's made of granite, so still stone structure. And this temple is particularly important because the father of Carnatic classical music, Purandara Dasa, spent many years composing and singing songs in praise of the deity in this temple. So Indian music has two big classical forms. One is the North Indian classical music and the second one is the South Indian classical music. The South Indian classical music is called Carnatic classical music. So Carnatic classical music did exist before the 15th century, but, you know, Purandara Dasa is given credit to have formed the structure of the fundamentals Carnatic classical music. He systemized the learning process into modules that are followed even in today's teaching. So that's why he is known as the father of modern, you know, Carnatic classical music, basically. He was a saint and composer. He is believed to have composed 475,000 compositions. There's no written record about that, though. There are about 2,000 compositions though that are available.

ASA Publications (10:15)

Wow, still. Okay, so how did you go about quantifying the room acoustic parameters of the worship spaces?

Braxton Boren (10:24)

So there's a well-established procedure, the ISO standard, ISO 3382, which is well known for how you take room acoustic impulse responses. The impulse response basically would be the response of the room to an infinitesimally short pulse, kind of like a Dirac Delta pulse, if you're in physics, or you might call it an indicator function if you're in mathematics, but just saying the shortest possible burst of sound that has equal energy at all frequencies. And the response of the room to that can give you lot of information about how it will affect every different frequency of sound. So, you know, the standard way you would do this in room acoustics is you then apply octave band filtering. So then you look at it at 500 hertz, you look at it at 1000 hertz, at 2000 hertz. And our ears have different sensitivities in these regions. And then you could apply different standard room acoustic parameters to these. So the reverberation time, which is the amount of time for the sound in that frequency to decay 60 decibels or approximately, until we can't hear it anymore, more or less. And then you also have something called the clarity index, which is often used for trying to quantify the clarity of sort of complex music, which has to do with the balance between the early reflections of sound, which help you understand complex pieces of music and the late sound, which tends to confuse your understanding of the music. And also the definition or D50 index, which is similar but specifically applied to speech intelligibility. These are, you know, again the standard things that you would do, and then we were also coming into this willing to accept that there might be other ways that we need to sort of analyze the data that would be more contextually appropriate to the Hindu worship service.

ASA Publications (12:14)

Okay, interesting, interesting. Was there anything that was specific to the Hindu worship space that was different from Christian or Islamic spaces?

Shashank Aswathanarayana (12:22)

So I think that's where the frequency analysis came into the picture. So we thought that, since there's not much done, we needed to kind of delve into the standard ones that are already there and perform frequency domain analysis because the sounds that we speak about, the chanting or the conch shells or the bells, they're all frequency focused, so to speak. So that's why we chose to do some frequency analysis.

ASA Publications (12:48)

Okay, so let's get more into frequency domain analysis. What is it and why did you include one in your examination of these spaces?

Braxton Boren (12:56)

Yeah, so a lot of the things we've talked about that came up in the context of Western worship space acoustics has to do mainly with the time domain. How is the sound decaying? What is the balance between sound reflections at different sort of time windows and how our ear is processing that? But yeah, for Hindu worship spaces, contextually, they tend to have things that are at very specific frequencies. So if you sound a conch shell, it will sound at one frequency and not another one. Whereas if you're listening to a sermon, like you can hear my voice right now, it's going up and down and changing its frequency all the time, right? And if you have a whole orchestra there, you might have a lot of different frequencies that you're going to care about over the course of an entire piece. But if you're mainly sounding a bell, if you're mainly looking at a conch shell, then those frequencies turn out to be much more important to the overall context of the worship service than some other frequencies as well. So you might want to asymmetrically look at those rather than treating all frequencies equally. And the other thing is that just looking at these spaces, they tend to be very rectangular and they're made of very reflective stone. So this is going to be very reflective and it's going to also tend to have prominent room modes, so there might be particular wavelengths that are emphasized more than other ones as well. So it makes sense to be thinking about it in the frequency domain as well as the time domain.

ASA Publications (14:22)

Okay, yeah, that totally makes sense. So what did you learn about the acoustics of these temples?

Shashank Aswathanarayana (14:27)

Yeah, well, I think some of our learnings was that these are smaller spaces compared to, you know, cathedrals and churches. They are rectangular and very reflective, as Braxton said earlier. And we found that the reverberation time is much larger in comparison to buildings of that size, basically. So that's one of our learnings. 

And another key learning from our analysis was that the C80 or the clarity index was very balanced, which basically promotes the listening to complex music passages clearly. So, you know, so that was another, learning. 

And, finally, there are two quantities called the resonance quality and resonance width that we looked at. These were two parameters introduced into the room acoustics literature just last year in a JASA paper published by Dr. Alaa Algargoosh, assistant professor at Virginia Tech University. So shout out to her. In her research, she showed how the resonance quality and resonance width of buildings can be looked at wherein certain numbers evoke higher emotional impact compared to smaller resonance quality and width. So the larger the resonance quality and width, the higher the emotional impact was. And these are the kind of numbers that we found in the two temples that we looked at as well.

ASA Publications (15:53)

Okay, okay, got it. What are the next steps in this research?

Shashank Aswathanarayana (15:58)

Well, the next steps… There are plenty of directions we could go in, but specifically we are looking at building computer models to further understand these spaces. So the research done so far is in the empty temples. So we could kind of build the models and then predict if the room was filled with people, how that would change the acoustics of the space. Also in one of the buildings, the Vijaya Vittala temple, a part of the roof has been broken down. So, you know, we could, using computer models, then predict how temple might have sounded back in the 15th century when it was intact.

ASA Publications (16:36)

Oh, that's a cool. Yeah.

Shashank Aswathanarayana (16:39)

And finally, we are progressing towards also understanding, you know having studied these two freestanding temples, as a next step, we are looking at cave temple research. So we are going a couple of centuries further back in history to look at cave temples in the same region.

ASA Publications (16:56)

Fun. Very cool. Do you have any other closing thoughts?

Braxton Boren (17:00)

Yeah, I would just say these are a kind of interesting template for a type of space that we see sometimes in the West, but we don't always think about them as much. Like we often think about room acoustics as this sort of spectrum between, maybe you have a classroom which is small and absorptive, and then you have something like, I don’t know, the Royal Albert Hall, which is large and reflective, or a big stone cathedral. But these are relatively small reflective spaces. But, if you think of, you know, your singing in the shower effect, you know, the shower is small but very reflective. But that's a, it's a sort of different space in that sort of two-dimensional space of different acoustics that you could think of. And even other spaces like Carnegie Hall exhibit something like this. They're a little bit smaller, but reflective, so they're able to change around some of the acoustic parameters in this way. So trying to understand these spaces, both the cave temples they evolved out of and the freestanding structures that come out of them. And also we're looking at much later Hindu temples as well here in America and back in India as well to try to understand how this type of acoustic space influences the reception of the soundscape in the Hindu worship service.

ASA Publications (18:12)

Shashank, did you have anything to add?

Shashank Aswathanarayana (18:14)

Yeah, just the fact that this is, you know, super exciting work. This is a new area of research, still very exploratory. So, you know, apart from comparison of Hindu spaces across different regions, we are also actually thinking of studying different religious spaces in the same region, right? Like, so take a city like New York or something like that, and then look at multiple worship spaces within that same city. So that is also something that we are thinking about, and we're excited by this.

Braxton Boren (18:44)

And also looking Christian churches in India as well. So you can look at the same geographical region there. What similarities and differences do we observe across religious traditions, but within the same general cultural grouping?

ASA Publications (18:58)

Right, right, I was just wondering that. Like if you have a bunch of different religious spaces that were created at the same time in the same area, would they have a lot of overlap just because everybody was thinking about kind of the same trends in design at the time for acoustics or not acoustics, but you know.

Shashank Aswathanarayana (19:18)

Yeah. And you know, some of them might not even be acoustics driven, just might be culturally driven. An interesting example we can give is a large church that Braxton and I visited in Chennai. Because of the weather conditions, you know, the windows are all open, so, you need some air circulation and flow, which not is common in Europe or the West.

ASA Publications (19:41)

Right, right, that totally makes sense. And that would definitely change everything in terms of sound.

Braxton Boren (19:47)

Yeah, so that's called the Santhome Cathedral in Chennai. Yeah, and it's kind of the opposite of what we've been talking about, in that we're talking about generally kind of small volume spaces that are very reflective, made of stone. That space is completely the opposite in that it's very large volume, similar to what you'd find in a European cathedral, but it's made highly of wood, which is more absorbent than stone. And then, yeah, it has tons of open window absorption, so you have a lot of lateral sound just escaping, but then a lot of reflections between the ceiling and floor.

ASA Publications (20:20)

Yeah. Thank you for talking with me today, guys. It is really so interesting to see how different religion services or style of worship can impact the design of a space. Thank you for shining some light on this fascinating topic, in particular with how it plays out in Hindu temples of yore. I wish you the best of luck in your future research, and have a great day.

Shashank Aswathanarayana (20:40)

Thank you so much, thanks for having us.