What is the difference between Sound Insulation and Sound Absorption?

Sound Insulation refers to a partition's ability to block sound from passing through it (measured by Sound Reduction Index, R), while Sound Absorption refers to a material's ability to reduce sound reflections within a room (measured by Absorption Coefficient, α). See Sections 3 & 4.

What does 'Flanking Transmission' mean?

It is the transmission of sound between two rooms by indirect paths, bypassing the main separating partition (e.g., through floors, ceilings, or side walls). See Clause 3.5.

What is 'Reverberation Time' (T or RT60)?

It is the time required for the sound pressure level in a closed space to decay by 60 decibels after the sound source has stopped. It is a primary indicator of a room's acoustic character. See Clause 5.1.

What is the Sound Reduction Index (R)?

Also known as Transmission Loss (TL), it is a measure in decibels of the sound insulation provided by a partition or material at a specific frequency. See Clause 3.2.

IS 9736

: 1981

Glossary of terms applicable to acoustics in buildings

CurrentSpecializedTerminologyBIMArchitectural · Functional Requirements in Buildings

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This standard serves as a glossary, defining technical terms used in the field of building acoustics. It covers fundamental concepts related to sound, its transmission, absorption, reverberation, and noise control, establishing a common vocabulary for professionals.

Glossary of terms applicable to acoustics in buildings

Quick Reference Values

Reference Sound Pressure (in air)2 x 10⁻⁵ N/m²

Reference Sound Intensity10⁻¹² W/m²

Frequency of Standard Tuning Fork (A)440 Hz

Typical Range of Human Hearing20 Hz to 20,000 Hz

Key Formulas

Lp = 20 log₁₀ (p / p₀) — Sound Pressure Level (dB)

R = 10 log₁₀ (1 / τ) — Sound Reduction Index (dB)

T = 0.161 V / A — Sabine's formula for Reverberation Time (seconds)

Practical Notes

This is a foundational terminology standard, not a design code; it defines 'what' a term means, not 'how much' is required.

While officially reaffirmed, many concepts are now elaborated in Part 8, Section 4 of the National Building Code (NBC) of India, which is used for practical design.

Essential for correctly interpreting acoustic test reports and material specifications from consultants and manufacturers.