Hinayana Buddhist Chaitya halls present one of the most magnificent concepts in the history of Architecture. The earliest of these halls have been dated back to 3^rd century B.C. and the latest to 2^nd century A.D. The most celebrated examples of these Chaitya halls, found all over India, are situated in the hillocks within a circle of about 60 km. radius around Poone. These halls are significant architectural events not only with respect to their unique concept, but also due to the artistry and effort behind their materialisation (rather un- materialization!) as well as the ingenuity with which they were treated to suit their functions. Percy Brown, the well known architectural historian denied the Chaitya halls the status of being architecture because they were not “good construction truthfully expressed” 1. But if emptiness (space) is the essence of architecture, as Lao Tse put it, a Chaitya hall should be considered as one nearest to the essence of architecture.

The word ‘Chaitya’ is derived from the Sanskrit root ‘Chi’, meaning to arrange or pile up in an orderly manner. ‘Chaitya’ meant a built up mound or structure and was used in this particular context to mean a funeral mound or even an enclosure containing a funeral mound. The ‘dagoba’ or the domical structure found at the far end of the Chaitya hall contained the relics of Buddhist Saints.

The Western historians have tried to compare chaitya halls with Greco-Roman basilicas or Christian Churches. However, some of them have ruled out any possibility of connection between the two contemporary developments of Chaitya halls and Basilicas2. Even though archaeologists have established that cultural and trade contacts had existed between Greco-Roman people and the people of the western coast of India during the period3, in all probability Chaitya halls and Basilicas are independent developments derived out of their different functional needs.

Chaitya halls are believed to be translations of independent timber structures which existed at the time of or prior to the former’s construction, in a new material, that is living rock. The most important proof which supports this view is the depiction of timber techniques of construction so faithfully executed even to details in rock cut form. In addition, decorative and pseudo structural timber work was profusely used as attached to the rock faces of the façade and interiors of these halls.

It has been shown further that such timbers elements were gradually abandoned as the architects and artisans of these halls familiarised themselves with the techniques of the new material. Instead of making and attaching timber elements, they started to chisel it down directly on rock. But, even after all after all the changes, the timber ribs fixed to the vault of the nave continued to be there almost invariably. This phenomenon went beyond the understanding of the historians, who thought it to be either a vestige of the ‘servile imitation’ or an inconsistency which need not be given much stress45.

At this juncture, it will be revealing to examine the functions of a Chaitya hall. It is known that the ‘Uposatta’ services of Buddhists were held in these halls. Such ceremonies typically included the repetition of the precepts of Buddhism, offering of flowers, the recitation of ‘Palisuttas’ and sermon by one of the monks for the visitors.6

Was the acoustical environment of the Chaitya hall interior well suited to this function?

A rough calculation of the reverberation time of a large Chaitya hall, using Sabines formula, without considering the deep timber ribs dowelled to the vault of the nave, will show that its value falls much above the permissible maximum for speech and hearing. For example, the value of reverberation time in the highly detailed Chaitya hall at Karli (80 B.C.) range between 3.5-4 seconds the total volume of the hall being about 4400 cu.m.7. Hence the speech articulation must be rather very poor. If the surface area of the ribs (about 1160m²) is also accounted with a min: absorption coefficient value of 0.1 for the timber surface the Reverberation time will become 2.5 S or less, an ideal value almost.

Further, the apsidal form of the Chaitya hall (derived from the need for circumambulation around the ‘dagoba’) and vaulted roof (a vestige of precedent timber buildings) would have caused an undesirably high concentration of sound, especially towards the apsidal end and a loud but blurred echo in the nave, but for the deep ribs in the soffit and the position of the ‘dagoba’ with its timber decorated base drum and Chhatri placed at a strategic position (See Fig.4).

The fact that such hall were continued to be made and use for about five centuries (B.C. 300 to AD 200) itself speaks about its efficacy. Hence it is only reasonable to surmise that the timber vaulted ribs were retained deliberately for acoustical purposes.

These ribs were made of sizable planks of teak wood89. The rib sizes of around 20 cms thickness and over 60 cms depth were used at a spacing of about 90 cms or less center to center in various Chaitya halls. They would affect the acoustical behaviour of vaulted ceiling in the following ways.

1. By forming elements which extend the path of sound rays (waves) especially at higher frequencies and reduce the intensity of them by multiple reflections on wood surface (See fig. 3).
2. By causing partial or full interference (cancellation) of sound waves, particularly at certain lower frequencies, depending on the depth and spacing of the ribs. The planks may dissipate lower frequency sound energy by panel vibrations also.
3. By preventing formation of sound foci due to specular reflections from the concave vault soffit (fig. 4) (This function is performed to some extent by the closely spaced columns in the horizontal plane).

The acoustical behaviour of the apsidal end and the half dome at the end of the vaulting also can create sound foci. But the position of a large ‘dagoba’ convex in shape, prevents the formation of the foci. The decorations with wood on the base of the ‘dagoba’ also helps in this respect10. The Chhatri and the ‘dagoba’ occupies the center of curvature of the semidome at the far end of the hall helping to diffuse the sound foci (See Fig. 4). The octagonal and circular columns, placed close to each other on the side of the aisles also scatter and diffuse the sound well. It has to be studied whether the aisles acting behind the closely spaced columns functions as slit resonators, in which case the reverberation time calculated earlier would have been much lesser at lower frequencies, resulting in better speech articulation.

In short, it has to be deduced that different elements have collaborated to produce a highly satisfactory acoustical condition in the hall. Among these, the timber ribs of the vaulted nave deserves special attention. But for hem, it was next to impossible for the interior of some of these halls to have served satisfactorily for its acoustic functions. Hence, the obstinate adherence of the makers of the Chaitya halls to the use of the ribs becomes especially conspicuous.

It is not argued here that the makers of Chaitya halls know all about the theory and application of acoustics as described earlier. But it would have been impossible for them to escape noticing the bad acoustical effects – echoes, sound foci, etc. in the absence of these deep timber ribs. This could be the only convincing explanation for the continued adherence to the use of such ribs. In fact these ribs look too slender in proportion and too deep to pass for a pseudo structural antic, nor were their springing points detailed to look like11. They were deliberately used for acoustical effect.

It may be seen that Chaitya halls with other shape and monolithic ribs cut in to the vault were also made, even though rarely, during the same period12. But after all trials and errors, towards the very end of the period the timber ribs reappear at the Kanhari hall (B.C. 180) to the surprise of historians wo were not aware of the fact that they were a proven acoustic by then.1314

It is not surprising that James Fergusson (writing in 1890 on these Chaitya halls) could not have understood the significance of the timber ribs and decorations to be acoustical treatments, sine at that time Architectural Acoustics in the west had not travelled much Vitruvius Pollio (B.C. 50) and W.C. Sabine had not yet initiated his historic investigations in room acoustics. It will be definitely interesting to take a fresh look at those magnificent interiors – this time with both eyes and ears open.

• 1. Page 19. Indian Architecture, Buddhist and Hindu Period by Percy Brown.
• 2. Ibid, Page 20.
• 3. See ‘History of Archeology of India’s contact with other countries from Earliest times to 300  BC’ by Shashi Asthana.
• 4. Brown, op cit, p. 20.
• 5. P.149, History of Indian and Eastern Architecture by J. Fergusson.
• 6. P.393, Encyclopedia Britannica (Macropodia) vol.2: Buddhism, Ceremonies and Festivals.
• 7. The reverberation time was calculated, taking an average absorption coefft. Of 0.02 for hard and smooth rocksurface. The absorption area of the intricate column Capitals and the Chaitya window and door openings were separately accounted. Absorption due to full and half audience were used.
• 8. Brown, op cit, p. 25. 
• 9. Fergusson, op cit, p 146. See footnotes which suggest that all wood work was done teakwood.
• 10. Fergusson, op cit, p 145.
• 11. Brown, op cit, Plate XIX. Unfortunately he has omitted all the decorations on the ‘dagoba’ in this sectional perspective. (Fergusson, op cit, p. 145-146)
• 12. In the Junar group of Chaitya hall there are rectangular and circula types with flat roof and without side colonnade. (Fergusson, op cit, P. 155)
• 13. See Description of the Chaitya hall at Kanheri (Fergusson, op cit, P. 162-164.). he describes the reappearance of timber ribs etc. as an “exceptional anomaly”.
• 14. Percy Brown identified the phenomenon as a “sign of deterioration” of style, even whilce he conceded that the plastic art embellishments and sculptures are of high quality (Brown, op cit, p. 26).