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IS 11050:2000 (Part 2) is the Indian Standard (BIS) for rating of sound insulation in buildings and of building elements, part 2: impact sound insulation. This standard specifies the method for calculating a single-number rating for the airborne sound insulation of building facades and facade elements. It involves comparing measured one-third octave band sound insulation data with a standard reference curve to derive the weighted standardized level difference (D2m,nT,w). The code also defines spectrum adaptation terms (C and Ctr) to evaluate performance against specific noise sources like traffic.
Rating of sound insulation in buildings and of building elements, Part 2: Impact sound insulation
Overview
Status
Current
Usage level
Specialized
Domain
Architectural — Functional Requirements in Buildings
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! The single-number rating D2m,nT,w is useful for comparison, but the spectrum adaptation term Ctr is critical for facades exposed to traffic noise, which is low-frequency dominated.
! This code is only for 'rating' measured data. The actual measurement procedure is detailed in IS 9901 (Part 5): Field measurements of airborne sound insulation of facade elements.
! A facade can meet the D2m,nT,w criteria but still have a significant acoustic weakness at a specific frequency, as an 8 dB unfavorable deviation is permitted at one frequency.
ISO 717-1:2020International Organization for Standardization (ISO), International
HighCurrent
Acoustics — Rating of sound insulation in buildings and of building elements — Part 1: Airborne sound insulation
Defines the single-number quantity (Rw) for airborne sound insulation, forming the basis for the IS code.
ASTM E413-16ASTM International, USA
MediumCurrent
Classification for Rating Sound Insulation
Provides a method for calculating a single-number rating (STC) for airborne sound insulation, analogous to Rw.
BS EN ISO 717-1:2020British Standards Institution (BSI), United Kingdom
HighCurrent
Acoustics. Rating of sound insulation in buildings and of building elements. Airborne sound insulation
The UK's national adoption of the ISO 717-1 standard, making it technically identical.
DIN EN ISO 717-1:2020-07Deutsches Institut für Normung (DIN), Germany
HighCurrent
Acoustics - Rating of sound insulation in buildings and of building elements - Part 1: Airborne sound insulation
The German national adoption of the ISO 717-1 standard, with identical technical procedures.
Key Differences
≠IS 11050 is based on an older version of ISO 717-1 (1996) and does not include the mandatory spectrum adaptation terms C and Ctr, which are required by the current ISO 717-1:2020 to account for different types of noise spectra (e.g., pink noise, traffic noise).
≠The standard frequency range for rating in IS 11050 is 100 Hz to 3150 Hz. While this matches the base range in ISO 717-1, the American standard ASTM E413 uses a different range of 125 Hz to 4000 Hz.
≠ASTM E413 imposes an additional constraint not found in IS 11050 or ISO 717-1: the maximum unfavorable deviation at any single one-third-octave band must not exceed 8 dB.
≠The rating nomenclature differs. IS 11050 and ISO 717-1 use the Weighted Sound Reduction Index (Rw), whereas the American equivalent ASTM E413 uses the Sound Transmission Class (STC). Due to different reference curves and frequency ranges, Rw and STC values are not directly interchangeable.
Key Similarities
≈Both IS 11050 and its international counterparts (ISO 717-1, ASTM E413) use the same fundamental methodology: comparing a measured sound insulation curve across one-third octave frequency bands to a standard reference curve.
≈The procedure for obtaining the single-number rating is similar. The reference curve is shifted in 1 dB steps until the sum of unfavorable deviations (where the measured performance is worse than the reference curve) is maximized but does not exceed a total of 32.0 dB.
≈The primary goal of all these standards is to simplify complex frequency-dependent data into a single-number rating (Rw or STC) to facilitate easy comparison, specification, and regulation of building elements' acoustic performance.
≈The shape of the reference curve used in IS 11050 is identical to the one specified in the ISO 717-1 standard it is based on.
Parameter Comparison
Parameter
IS Value
International
Source
Primary Rating Metric
Weighted Sound Reduction Index (Rw)
Sound Transmission Class (STC)
ASTM E413-16
Frequency Range for Rating
100 Hz - 3150 Hz
125 Hz - 4000 Hz
ASTM E413-16
Sum of Unfavourable Deviations (Max)
32.0 dB
32 dB
ISO 717-1:2020
Maximum Single Unfavourable Deviation
Not specified
8 dB
ASTM E413-16
Spectrum Adaptation Terms
Not included
C and Ctr (mandatory to report)
ISO 717-1:2020
Rating Value Definition
Value of the shifted reference curve at 500 Hz
Value of the shifted reference curve at 500 Hz
ISO 717-1:2020
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Evaluation frequency range100 Hz to 3150 Hz
Number of one-third octave bands for evaluation16 bands
Maximum unfavorable deviation at any single frequency8.0 dB
Maximum sum of unfavorable deviations over all frequencies32.0 dB
Key Formulas
D_2m,nT,w = Value of the shifted reference curve at 500 Hz
C = L_A,spectrum1 - L_A,Rw — Spectrum adaptation term for pink noise
C_tr = L_A,spectrum2 - L_A,Rw — Spectrum adaptation term for traffic noise
Tables & Referenced Sections
Key Tables
Table 1: Values for the reference curve
Table A.1: Reference pink noise spectrum
Table B.1: Reference traffic noise spectrum
Key Clauses
Clause 5: Procedure for evaluating the single-number quantity
Clause 6: Procedure for evaluating the spectrum adaptation terms C and Ctr
Annex A: Spectrum adaptation term C for pink noise
Annex B: Spectrum adaptation term Ctr for traffic noise
Frequently Asked Questions4
What does D2m,nT,w stand for?+
It is the 'Weighted Standardized Level Difference', a single-number quantity representing the airborne sound insulation of a facade, calculated as per this standard.
Why is the Ctr value important for a facade?+
Ctr is a spectrum adaptation term that adjusts the rating for traffic noise. A large negative Ctr value indicates poor performance against low-frequency traffic sounds, even if the D2m,nT,w rating is high.
What is the main output of this standard?+
The main output is a set of three numbers for a facade element: D2m,nT,w (C; Ctr), for example: 35 (-1; -5) dB. This provides a comprehensive rating.
Does this standard provide design values for facades?+
No, it only provides the method to rate the performance based on acoustic test results. It does not give prescriptive design requirements.