सोपानम् ६: बाह्य-प्रयत्नः (The 11 External Efforts)
Sopāna 6: Acoustic Phonation Mechanics — Khar vs. Haś (Unvoiced/Voiced), Alpa/Mahāprāṇa (Aspiration), and Pitch Accents
१. दर्शनम् — Acoustic Release Dynamics
"बाह्यप्रयत्नस्त्वेकादशधा — विवारः संवारः श्वासो नादो घोषोऽघोषोऽल्पप्राणो महाप्राण उदात्तोऽनुदात्तः स्वरितश्चेति।"
bāhyaprayatnastv ekādaśadhā — vivāraḥ saṃvāraḥ śvāso nādo ghoṣo'ghoṣo'lpaprāṇo mahāprāṇa udātto'nudāttaḥ svaritaśceti |
— वरदराजः, लघुसिद्धान्तकौमुदी (संज्ञा-प्रकरणम्)
"External effort (occurring after air passes the vocal cords) is elevenfold: 3 Unvoiced (Vivāra, Śvāsa, Aghoṣa) + 3 Voiced (Saṃvāra, Nāda, Ghoṣa) + 2 Aspiration (Alpaprāṇa, Mahāprāṇa) + 3 Vowel Pitch Accents (Udātta, Anudātta, Svarita)."
While Ābhyantara Prayatna (आभ्यन्तर-प्रयत्नः) governs the intra-oral contact of the vocal organs, Bāhya Prayatna (बाह्य-प्रयत्नः) determines the acoustic quality of the sound wave at the vocal cords and glottis.
This division creates the fundamental grammatical distinction between कठोर (Hard / Unvoiced) and मृदु (Soft / Voiced) consonants that powers all Sandhi operations.