Origin and Propagation of Sound (शब्दोत्पत्तिः प्रसारश्च)

Theories about the Origin and Propagation of Sound (Samskrit: शब्दोत्पत्तिः प्रसरणश्च) have well been discussed in many ancient texts of Bharatavarsha.

• Sankhya siddhanta holds that the ear (श्रोतेन्द्रियं) travels to the source of sound and grasps the sound
• Nyaya and Vaiseshika systems put forth that sound travels like waves in Akasha (ether) and gets perceived in the ear (श्रोतेन्द्रियं).
• Mimamsakas held that vibrations of air particles which reach the ear-drum manifest Shabda and that these vibrations have a higher amplitude (called naada) when many people utter the shabda simultaneously. They also clarified that Shabda does not constitute of Vayu (air).

Many modern findings have confirmed the above theories and we now study that sound is a form of energy which is transmitted by the vibration of particles in any medium.

परिचयः ॥ Introduction

Sound according to the modern physical science research is a form of very weak energy. It travels in space in wave form all round and within the ear space in the auditory canal. so if some sound is created, say by utterance or by the clink of a vessel or the ring of a bell, it travels all around in waves and enters the ear-space of one within reach. The sound waves are not audible by themselves. But when the sound-waves enter the ear-space the waves strike the walls of the ear and get deflected towards the diaphragm within, which is super sensitive to even mild waves and oscillates, thereby activating the motor nerves to transmit the message to the brain, where the message is converted into sound that we recognize. Here it is to be noted that the sound wave by itself is not audible; and does not produce sound. It is the resonance of air in a bounded space that produces sound. This is experimentally verified and demonstrated in classes. Every day, aeroplanes fly past us, but we do not hear them. But in a cloudy atmosphere, sound of the aeroplane flying by is heard clearly. The more cloudy the space, the louder will be the sound. Because in the bounded space, there will be reverberations, the clash of waves to and fro, that create the sound. The same principle works in the ear also.

In this article we discuss about the Science of Dhvani (ध्वनिविज्ञानम्), the physics of sound in ancient days in comparison with modern knowledge of the science of sound. It is to be noted that the siddhantas about the specialized subjects of origin of sound, the production of articulated words by humans vocal organs, the transmission of sound requiring a medium, the wave theory for the propagation of sound - were explored and put forth much before the advent of modern experimental instruments and availability of specialized testing systems.

शब्दोत्पत्तिः ॥ Origin of Sound

Maharshi Kanada explains about the characteristics of various things in the world (padarthas) in his Vaiseshika Sutras. While explaining that sound is something that is heard (Vais. Sutr. 2.2.21), he identifies the various ways in which sound is produced and concept of Sound arising from Sound, which is one of the fundamental aspects of modern physics, as follows

संयोगाद्विभगाच्च शब्दाच्च शब्दनिष्पत्तिः। (Vais. Sutr. 2.2.31)

Sound is produced from conjunction (संयोगात्) disjunction (विभागात्) and from sound (शब्दात्) also.

From conjunction, i.e., from conjunction of the drum and the stick, from disjunction, i.e., when a bamboo stick is being split up and where Sound is produced in a distant flute and such other instruments, Sound is produced. Such sound reaches the portion of the ether of ear hollow and thereby gets heard.

शब्दोत्पत्तिप्रक्रिया ॥ Science of Speech Production

Having seen the details about external sounds from instruments etc, we now deal with production of Articulated sounds namely Varnas. They are also called Syllables or independent units of cognizable sounds characterized by having specific vocal location and mechanism of utterance (उच्चारणस्थानानि and वाग्यन्त्राणि). Articulate sentences or speech (Vak) gives birth to a language and plays an exceedingly important role in activating the world; all the more important at the time when Vedas were only transmitted by oral tradition. Thus its not out of place to mention that science of speech was well studied in the vedic times and the texts of Shiksa shastra (among the Shad Vedangas) Pratisakhyas and Shiksa granthas deal with the science of words, their production, pronunciation and accent. Perhaps nowhere is such an amount of technical literature available on grammar, phonetics and related topics as in Samskrit. Phonetics is as old as the Vedas.

Language is born, when a living being desires to express himself. It is that fire that is lit by the coming together of anubhava or experience and vivakshaa or a desire to express.Paniniya Shiksha gives a deft description of the process involved in uttering a word from the mouth as follows

Process of Production of Articulate Sounds in a Human

आत्मा बुद्ध्या समेत्यार्थान्मनो युङ्क्ते विवक्षया। मनः कायाग्निमाहन्ति स प्रेरयति मारुतम् ।।6।।

मारुतस्तूरसि चरन्मन्द्रं जनयति स्वरम्। प्रातःसवनयोगं तं छन्दो गायत्रमाश्रितम् ।।7।।

कण्ठे माध्यन्दिनयुगं मध्यमं त्रैष्टुभानुगम्। तारं तार्तीयसवनं शीर्षण्यं जागतानुगम्।।8।।

सोदीर्णो मूर्धन्यभिहतो वक्त्रमापद्य मारुतः। वर्णाञ्जनयते तेषां विभागः पञ्चधा स्मृतः।।9।।

स्वरतः कालतः स्थानात्प्रयत्नानुप्रदानतः। इति वर्णविदः प्राहुर्निपुणं तन्निबोधत ।।10 ।। (Pani. Shik.)

1. The Atman inspires the Buddhi (intellect) and a thought formulates.
2. Combined with Vivaksha (विवक्षा) an intent of the person to express himself.
3. Manas desires to utter syllables and air is activated in the thoriacic region.
4. The air travels upwards and gets modified at different levels in the vocal tract - vocal cords and articulators.
5. This modified air is called sound, the primary unit of speech.

Thus Atman, Mind, Air and Articulators are considered to be the prerequisites for speech production.

Varnas or Speech sounds are generated on the basis of the following 1) Pitch (Svara) 2) Quantity (Kala) 3) Place of articulation (Sthana) 4) Effort (Prayatna) 5) Sound material (Anupradana)

वर्णोच्चारणस्थानानि or the Places of articulation of various sounds are eight were determined as follows.

अष्टौ स्थानानि वर्णानामुरः कण्ठः शिरस्तथा। जिह्वामूलं च दन्ताश्च नासिकोष्ठौ च तालु च।।1 ।3।। (Pani. Shik.)

1. Chest (उरः)
2. Throat (कण्ठः)
3. Head (शिरः)
4. Alveolus (जिह्वामूलं) the base of the tongue
5. Teeth (दन्ताः)
6. Nose (नासिका)
7. Lips (ओष्ठौ)
8. Soft palate (तालु)

शब्दप्रसरणसिद्धान्ताः ॥ Propagation of Sound

This section answers how sounds after originating travel in a medium to reach the auditory sense organ namely the ear.

Bhashapariccheda

For this two theories are proposed, as given by Visvanatha of Bhashapariccheda.

Theories of Propagation of Sound (वीचीतरङ्गन्यायः and कदम्बमुकुलन्यायः)

वीचीतरङ्गन्यायेन तदुत्पत्तिस्तु कीर्तिता । कदम्बगोलकन्यायादुत्पत्तिः कस्यचिन्मते ।। (Bhas. Pari. 166)

Its (sound's) origination is said to take place in the manner of waves. According to some the origination is in the simultaneous manner of the opening of Kadamba buds.

According to the concept of Ripple wave effect (वीचीतरङ्गन्यायम् an anology for longitudinal waves) sound travels in a wave pattern by creating ripples in the medium just like circular waves in a lake which are generated and travel outward in all directions, from the spot where the stone was dropped. One may note the time lapse between the first wave generated and the last wave that reaches the shore before it disappears. According to the concept of unfolding of Kadamba bud (कदम्बमुकुलन्यायम् an analogy for transverse waves) at one instance, sound generated will be further produce multiple sound instances at a single point which in turn generate more sound; thus a simultaneous sound production effect is noted.

Mimamsa

According to Dr. Sivasenani Nori, Sabarabhashya on the Jaimini Mimamsa sutra (1.1.13) gives a remarkably identical description of production and propagation of sound as that given by text of modern Physics.

Sound Waves : Sound is produced in the form of waves, each wave generating the next one.

सतः परम् अदर्शनं विषयानागमात् ॥ MS_१,१.१३ (Mima. Sutr. 1.1.13)

Shabara Bhashya is as follows

तच्च संयोगविभागसद्भावे सति भवतीति संयोगविभागाव् एवाभिव्यञ्जकाव् इति वक्ष्यामः। उपरतयोः संयोगविभागयोः श्रूयत इति चेत्. नैतदेवम्। न नूनमुपरमन्ति संयोगविभागाः, यत उपलभ्यते शब्द इति। न हि ते प्रत्यक्षा इति।

.......

अभिघातेन हि प्रेरिता वायवस्तिमितानि वाय्वन्तराणि प्रतिबाधमानाः सर्वतोदिक्कान् संयोगविभागानुत्पादयन्ति। यावद्वेगमभिप्रतिष्ठन्ते। ते च वायोरप्रत्यक्षत्वात्संयोगविभागा नोपलभ्यन्ते। अनुपरतेष्वेव तेषु शब्द उपलभ्यते नोपरतेषु। अतो न दोषः। अत एव चानुवातं दूरादुपलभ्यते शब्दः ।। (Bhas. Mima. Sutr. 1.1.13)

As long as compressions and expansions (saṃyogavibhāgau) [of air particles] are present, Śabda is heard. Therefore we say that compressions and expansions are the manifesters of Śabda. If it be said that Śabda is heard after compressions and expansions have stopped, it is not so. The compressions and expansions, from which Śabda is perceived, do not cease. It is only that these compressions and expansions cannot be directly perceived.

........

The air particles propelled by the stroke hit against other unagitated air particles and produce compressions and expansions on all sides. These compressions and expansions subsist as long as the impetus lasts. Since air cannot be directly perceived these compressions and expansions are not visible. Śabda is heard only as long as these compressions and expansions do not cease, but not after they cease. . . . This is the reason Śabda is heard for longer distances downwind.

Demonstration of Transverse propagation of sound waves by alternating compressions and rarefactions

An extract is given from a modern textbook (Singh, Singh Sardar. Longman science Physics 9. New Delhi: DK Publishers, 2009. pp. 107, 108), with the Sanskrit text from Śābarabhāṣya (अभिघातेन हि प्रेरिता वायवस्तिमितानि वाय्वन्तराणि प्रतिबाधमानाः सर्वतोदिक्कान् संयोगविभागानुत्पादयन्ति।) superimposed on the text at appropriate places.

1. Consider the original position of layers of air when no sound wave exists (Fig. 5.2(a)).
2. Now strike a tuning fork against a rubber pad (अभिघातेन हि), so that both the prongs P1 and P2 begin to vibrate. For convenience we shall consider the motion of only one prong, say P2. When the prong P2 moves to the right it pushes the layer of air adjacent to it (प्रेरिताः वायवः). This creates a region of high pressure close to the prong P2. The air gets compressed (or a compression is formed) Fig. 5.2(b).
3. This compression is passed on to the next layers by the vibrating air layers स्तिमितानि वाय्वन्तराणि प्रतिबाधमानाः). The layers vibrate back and forth about their mean positions and the disturbance, in the form of compression, moves on. When P2 moves to the left of the original position (Fig. 5.2(c)) and leaves a region of low pressure on the right side, the layers move apart to form a rarefaction.
4. In the rarefaction, the particles are farther apart than normal. Like in the case of compression, the rarefaction is also passed on to the adjacent layers. A compression is always followed by a rarefaction, which is again followed by a compression (संयोगवियोगान् उत्पादयन्ति।). This process is repeated so long as the tuning fork is vibrating (यावद्वेगमभिप्रतिष्ठन्ते।).
5. Thus, the net effect of a vibrating tuning fork is that it sends out the waves consisting of alternate compressions and rarefactions in the air (Fig. 5.2 (d)).