Rating of sound insulation in buildings and building elements, Part 3: Airborne sound insulation of facade elements and facades
1984 Edition

Scope and Application Area of This Standard

• Defines measurement methods for airborne sound insulation using one-third octave band analysis as per ISO 140/3 and ISO 140/5.
• Applicable to external building components and facades for assessing airborne noise reduction.

Reference Values and Tables

• Reference data for comparison are specified in Table 3.
• These frequency-dependent values are used to derive single-number ratings.

Overview of Relevant Tables

Common Formula for Single-Number Rating (e.g., Rw):

[ R_w = -10 \log_{10} \left( \frac{\sum_i 10^{-0.1 R_i} w_i}{\sum_i w_i} \right) ]

• (R_i): Sound reduction index at each frequency band
• (w_i): Weighting factor from the reference curve

flowchart LR
    A[Measure in 1/3 Octave Bands] --> B[Extract R_i Values]
    B --> C[Compare Against Reference Values (Table 3)]
    C --> D[Compute Single-Number Rating]
    D --> E[Evaluate Airborne Sound Insulation]

Summary: Establishes standardized procedures for measuring and assessing airborne sound insulation of facades, utilizing frequency bands and reference curves to derive uniform single-number ratings.

Normative References and Key Specifications

Reference Values (Clause 4.2 and Table 3)

• Used as benchmarks for measured sound insulation values (R, Rtr, Rg, etc.) across one-third octave bands:

Comparison Method (Clause 4.3)

• The reference curve is shifted in 1 dB increments toward the measured data.
• Calculate the mean negative deviation where measured values fall below references, averaged over 16 frequencies.
• The shift is maximized with mean negative deviation not exceeding 2.0 dB.
• The rating (e.g., Rw) is the shifted reference value at 500 Hz.
• Record any maximum negative deviation greater than 8 dB.

Single-Number Ratings (Tables 1 & 2)

Process Summary

flowchart TD
    A[Obtain R, Rtr, etc. measurements] --> B[Compare with Reference Values]
    B --> C[Shift Reference Curve]

Key Terms and Definitions for Airborne Sound Insulation

Single-Number Quantities (Tables 1 & 2)

Reference Values (Table 3)

Comparison Technique

• Shift the reference curve incrementally until the average negative deviation is at most 2.0 dB.
• The shifted reference value at 500 Hz represents the rating.

Procedure for Deriving Single-Number Acoustic Ratings

This part corresponds to ISO 717 and ISO 140 standards for airborne sound insulation.

Highlights:

• Single-number ratings condense detailed frequency data into an easy-to-use index.
• Different terms apply depending on measurement context:
  • Table 1 details terms for exterior building components.
  • Table 2 covers facade sound protection terminology.

Steps:

1. Measure airborne sound insulation in one-third octave bands as per ISO 140/3 and ISO 140/5.
2. Apply frequency weighting curves to the measured data.
3. Calculate the rating by comparing weighted data to the reference curve.

Representative Formula:

[ R_w = -10 \log_{10} \left( \sum_{i} 10^{-R_i/10} \times \Delta f_i \right) ]

• (R_i): Sound reduction index at frequency band (i)
• (\Delta f_i): Bandwidth factor (generally constant for 1/3 octave bands)

Summary Tables:

flowchart TD
    A[Measure sound insulation (1/3 octave bands)] --> B[Apply frequency weightings]
    B --> C[Compute single-number rating]
    C --> D[Incorporate into building regulations]

Refer to ISO 140/3 and ISO 140/5 for detailed measurement and calculation procedures.

Guidelines for Reporting Acoustic Ratings and Results

Comparison Method (Clause 4.3)

• Shift the reference curve in 1 dB steps toward the measured data.
• Calculate the mean negative deviation where measured values are less than reference values, averaged over 16 frequencies.
• Continue shifting until mean negative deviation is maximized but does not exceed 2.0 dB.
• The final rating (Rw, Rtr,w, etc.) is the shifted reference value at 500 Hz.
• Report maximum negative deviations exceeding 8 dB.

Reporting Requirements (Clause 5)

• Provide the single-number rating.
• Include the maximum negative deviation if it exceeds 8 dB.
• Present measured data and the shifted reference curve graphically as per ISO 140/3 and ISO 140/5.

Reference Values (Table 3)

Summary Table of Single-Number Ratings

Reference Levels for Airborne Sound Insulation

Fundamental Concepts:

• Single-number ratings are weighted values derived from one-third octave band measurements.
• The rating process involves shifting a reference curve in 1 dB increments to minimize negative deviations.
• The average negative deviation should not exceed 2 dB; any frequency with deviation over 8 dB must be recorded.

Important Tables:

Table 1: Single-number ratings for exterior building components

Table 2: Single-number rating for facade airborne sound insulation

Table 3: Reference sound insulation values (dB)

Procedure for Comparing Measured Airborne Sound Insulation to Reference Values

Highlights from Clause 4.3:

• The reference curve provided in Table 3 is shifted in 1 dB increments toward the measured sound insulation curve.
• Calculate the mean negative deviation where measured values are lower than the reference, averaged over 16 frequency bands.
• The shifting process continues until the mean negative deviation is maximized without exceeding 2.0 dB.
• The weighted sound reduction index (e.g., Rw) is the value of the shifted reference curve at 500 Hz.
• Any maximum negative deviation exceeding 8.0 dB must be documented.

Reference Values Table (dB) for Frequencies (Hz)

Formula for Mean Negative Deviation

[ \text{Mean Negative Deviation} = \frac{\sum (\text{Reference} - \text{Measured})_{\text{positive only}}}{16} \leq 2.0 \text{ dB} ]

Reporting Instructions (Clause 5)

• Report the single-number rating (Rw, Rtr,w, etc.).
• Document maximum negative deviations above 8 dB.
• Provide graphical representation including shifted reference curve as per ISO 140/3 and ISO 140/5.

Airborne Sound Insulation for Facade Elements and Full Facades

This part addresses airborne sound insulation performance of facade components such as windows, doors, roofs, and curtain walls.

Core Concepts and Formulas

• Sound Reduction Index (R): Quantifies the sound transmission reduction capability of a facade element. [ R = 10 \log_{10} \left(\frac{1}{T}\right) ] where (T) is the sound transmission coefficient.

• Weighted Sound Reduction Index (R_w): A single-number value derived from frequency-specific R values, enabling standardized comparison.

• Facade Sound Insulation Index (D2m,nT,w): Considers outdoor sound pressure and indoor reverberation to express facade sound insulation.

Typical Ratings for Common Facade Elements

Design Recommendations

• Employ multiple glazing layers for improved noise reduction.
• Ensure airtight sealing around facade components to prevent sound leaks.
• Combine facade elements with internal sound-absorbing materials to boost overall performance.

flowchart LR
  A[External Noise] --> B[Facade Component]
  B --> C[Sound Transmission]
  C --> D[Indoor Noise Level]
  B --> E[Calculate Sound Reduction Index (R)]
  E --> F[Derive Weighted Index (R_w)]
  F --> G[Determine Facade Sound Insulation (D2m,nT,w)]

For field measurement details, consult IS 11050 Part 5.

Understanding Weighted Sound Reduction Indices

Overview:

• Indices such as Rw, Rtr,w, Row, and Re,oc,w represent single-number evaluations derived from measurements in one-third octave frequency bands.
• These indices assess airborne sound insulation for building components and facades.

Comparison Method (Clause 4.3):

• The reference curve is adjusted in 1 dB increments toward the measured data.
• Calculate the mean negative deviation only where measured values are below the reference.
• The shift is optimized so that the mean deviation does not exceed 2 dB.
• The shifted reference value at 500 Hz yields the weighted index (e.g., Rw).
• Maximum negative deviations over 8 dB are recorded and reported.

Reference Values for Airborne Sound (Table 3)

Summary of Single-Number Metrics (Tables 1 & 2)

Weighted Standardized Level Difference (DnT,tr,w) in Accordance with This Standard

Concept:

• Represents a single-number rating expressing airborne sound protection offered by facades.
• Derived from standardized level differences (DnT,tr) measured in one-third octave bands.
• Determined by shifting a reference curve to best fit measured data.

Procedure (Clause 4.3):

1. Measure DnT,tr values across one-third octave bands with adequate precision.
2. Shift the reference curve from Table 3 in 1 dB increments toward measured values.
3. Calculate mean negative deviation where measured values are less than reference.
4. Stop shifting when mean deviation is at or below 2 dB and maximized.
5. The shifted curve value at 500 Hz is recorded as DnT,tr,w.
6. Document any maximum negative deviation exceeding 8 dB.

Reference Values (Excerpt from Table 3)

Summary Formula:

• DnT,tr,w equals the reference curve value at 500 Hz after optimal shifting.

graph LR
A[Measured DnT,tr Data] --> B[Compare with Reference Curve]
B --> C{Shift Reference Curve in 1 dB Steps}
C --> D[Compute Mean Negative Deviation]
D --> E{Deviation ≤ 2 dB?}
E -- Yes --> F[Record DnT,tr,w at 500 Hz]
E -- No --> C

Requirements for Reporting and Documentation

Essential Points:

• Single-number ratings (e.g., Rw, Rtr,w, DnT,tr,w) are calculated from one-third octave band measurements following ISO 140/3 and ISO 140/5.
• Reference sound insulation values per frequency are provided in Table 3.

Comparison Method (Clause 4.3):

• Shift the reference curve in 1 dB increments toward the measured results.
• Calculate mean negative deviation where measured data fall below references.
• The shift stops when mean deviation ≤ 2 dB and maximum negative deviation ≤ 8 dB.
• The rating at 500 Hz on the shifted curve is reported.
• Maximum negative deviations above 8 dB must be explicitly noted.

Documentation (Clause 5):

• Report the calculated single-number rating referencing ISO 717.
• Include maximum negative deviation if it exceeds 8 dB.
• Provide graphical plots showing measured data and the adjusted reference curve per ISO 140/3 and ISO 140/5.

flowchart TD
    A[Measure sound insulation (1/3 octave bands)] --> B[Compare with reference values (Table 3)]
    B --> C[Shift reference curve in 1 dB steps]
    C --> D[Calculate mean negative deviation]
    D --> E{Deviation ≤ 2 dB?}
    E -- Yes --> F[Report single-number rating]
    E -- No --> C

Related Standards Referenced by This Part

This standard incorporates and aligns with ISO 717-3 (1982) for airborne sound insulation testing and evaluation.

Key Reference Tables

Reference Sound Insulation Values (Table 3)

Single-Number Ratings (Tables 1 & 2)

Comparison Process (Clause 4.3)

• Shift the reference curve in 1 dB increments toward measured values.
• Calculate mean negative deviation only where measured data fall below reference.
• Maximize mean deviation without exceeding 2 dB.
• The rating (Rw or equivalent) is the shifted reference value at 500 Hz.