Quickly look up key sound insulation index, acoustic indicators, noise measurement standards, impact sound & reverberation time in building design with DASM – According to international ISO standards.
Key sound insulation index
In the field of acoustics, there are many concepts, indices, and quantities that you may not be familiar with or have heard of but often confuse. Let’s review the common basic acoustic indices and concepts together right below.
‘A’ FREQUENCY WEIGHTING:
The ‘A’ frequency weighting is the most widely used scale for assessing occupational and environmental noise. However, environmental noise evaluations often require adjustments to reflect the acoustic characteristics more accurately.
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‘F’ (FAST) TIME WEIGHTING:
Designed for a time constant of 0.125 seconds in sound level meters.
‘S’ (SLOW) TIME WEIGHTING:
Designed for a time constant of 1 second in sound level meters.
‘Z’ FREQUENCY WEIGHTING:
The ‘Z’ (Zero) frequency weighting has a flat response (0 dB) from 10 Hz to 20 kHz in 1/3 octave bands, within tolerance limits set by AS IEC 61672.1-2004.
1/3 OCTAVE BAND:
A frequency band where the range is divided into thirds, enabling more detailed analysis—each band spans 23% of its center frequency.
ACOUSTICS:
The science of sound dealing with generation, transmission, effects on hearing, measurement, control technology, and practical applications.
AIRBORNE SOUND INSULATION:
Measures the reduction of sound energy passing through a construction element, accounting for acoustic conditions in the receiving room.
AMBIENT NOISE:
The overall background noise at a given location from all nearby and distant sources—traffic, machinery, wind, insects, animals, etc.—typically measured as LAeq,T.
APPARENT SOUND REDUCTION INDEX (R’):
Ten times the logarithm of the ratio between the power of the incident sound (W1) and the sum of transmitted sound (W2) and flanking transmission (W3) into the receiving room.
AUDIBLE:
Sound that is perceivable, ranging from barely detectable to clearly noticeable or prominent.
A-WEIGHTED SOUND PRESSURE LEVEL (dBA):
A measurement using the A-weighting filter to assess noise sensitivity, especially in the mid- to high-frequency ranges.
BACKGROUND NOISE (FOR BUILDINGS):
Residual noise level in a building when the sound source under evaluation is not active.
BUILDING ACOUSTICS:
A sub-discipline of acoustics that addresses indoor sound behavior, external sound intrusion, and noise generated by mechanical and electrical systems in buildings.
C-WEIGHTED SOUND PRESSURE LEVEL (dBC):
Used to evaluate low-frequency noise down to 35 Hz using the C-weighting filter.
CORRECTION TO THE BACKGROUND NOISE:
Adjusting measurements by subtracting background noise in logarithmic terms.
DAYTIME-EVENING-NIGHT LEVEL (Lden):
Describes long-term average A-weighted sound levels over day, evening, and night periods.
ELEMENT-NORMALIZED LEVEL DIFFERENCE (Dₙ,e):
Level difference normalized to reference absorption area in the receiving room, assessing transmission through a specific element.
ENVIRONMENTAL OR EXTERNAL NOISE:
Undesirable or harmful airborne noise from traffic, machinery, industrial operations, and recreational areas.
Correct source identification is key to optimal sound insulation design.
EQUIVALENT CONTINUOUS SOUND PRESSURE LEVEL (Leq):
The average sound pressure level over time T, reflecting energy-equivalent continuous noise (referred to as LAeq with A-weighting).
FREQUENCY SPECTRUM:
Graphical representation of sound pressure level across octave or 1/3 octave bands.
NOISE REDUCTION COEFFICIENT (NRC):
A single number (0.0–1.0) representing a material’s average sound absorption in the mid-frequency range. An NRC of 0.0 reflects total sound reflection.
IMPACT ISOLATION CLASS (IIC):
A single-number rating indicating floor/ceiling system impact sound insulation. Higher IIC means better impact noise reduction.
IMPACT SOUND INSULATION (LnT,w):
Standardized impact sound pressure level (LnT,w) per ISO 717-2:2004. Lower values indicate better insulation.
IMPACT SOUND PRESSURE LEVEL (Lᵢ):
Average energy level in 1/3 octave bands measured in the receiving room under standard impact excitation.
IMPULSE SOUND INSULATION:
Measures resistance to sudden impulse noise (e.g., footsteps, dropped objects) transmitted through building structures.
IMPULSE SOUND PRESSURE LEVEL (Lᵢ):
Average impulse sound level measured during testing with a standard impulse sound source.
IMPULSE SOUND:
Generated from direct structural impacts (e.g., footsteps, door slams) that travel through the building frame.
INDOOR NOISE OR INNER NOISE:
Unwanted noise from mechanical and electrical installations or nearby activities that negatively affect occupants.
LOUDNESS:
A subjective measure of perceived sound intensity. A 10 dB increase is perceived as a doubling of loudness.
MAXIMUM SOUND PRESSURE LEVEL (L_F,max):
Highest sound pressure level recorded with fast time weighting in a given octave band.
NOISE CRITERION (NC) LEVELS:
A system primarily used in North America to assess indoor noise environments.
NOISE RATING (NR) CURVES:
International ISO standard for defining acceptable indoor noise levels based on activity and comfort.
NOISE REDUCTION INDEX (R):
Logarithmic value quantifying how much sound energy a building element reduces between two spaces.
NOISE:
Unwanted or harmful sound. Noise can also include vibrations and is considered undesirable acoustic energy.
NORMALIZED IMPACT SOUND PRESSURE LEVEL (Ln):
Impact sound pressure level adjusted for absorption in the receiving room relative to a reference room.
OCTAVE BAND:
Frequency range where the upper limit is twice the lower limit, centered around a defined frequency.
PINK NOISE:
Broadband noise with equal energy per octave, emphasizing lower frequencies. Commonly used in acoustic testing.
RECEIVER ROOM:
The room where transmitted sound is measured in sound insulation tests.
REVERBERATION TIME (T):
Time it takes for sound to decay by 60 dB after the source stops. Key indicator of acoustic performance.
SOUND POWER LEVEL (Lw):
Total sound energy emitted by a source, expressed in decibels relative to 10⁻¹² watts.
SOUND PRESSURE LEVEL (Lp):
Sound level at a point, calculated using the logarithm of the measured pressure over a reference pressure.
SOUND TRANSMISSION CLASS (STC):
A single-number rating for a partition’s ability to block airborne sound.
SOUND TRANSMISSION LOSS (STL):
Measures how well a material or structure attenuates sound transmission, expressed in dB.
SOURCE ROOM:
The room containing the noise source during acoustic transmission tests.
SPECTRUM ADAPTATION TERMS (Ctr, C, CI, etc.):
Adjustment terms calculated under ISO 717-1 and 717-2 to refine sound insulation ratings for specific noise profiles.
WEIGHTED IMPULSE NOISE ISOLATION INDEX (ΔLw):
Indicates improvement in impact noise insulation using standardized reference curves.
WEIGHTED NOISE REDUCTION INDICES (Rw, R’w):
Single-number sound insulation ratings based on reference curves and adjusted for performance.
WEIGHTED SOUND ABSORPTION COEFFICIENT (αw):
Single-number rating of a material’s sound absorption performance based on standardized references.
WEIGHTED SOUND REDUCTION ENHANCEMENT INDEX (ΔRw):
Indicates improved sound insulation (ΔR) using 1/3 octave band reference curves.
WEIGHTED STANDARDIZED FAÇADE LEVEL DIFFERENCE (D₂m,nT,w):
Difference in sound pressure level between the external façade (2 m away) and interior, corrected for reverberation time.
WEIGHTED STANDARDIZED IMPULSE SOUND PRESSURE LEVEL (LnT,w):
Weighted impulse sound response in the receiver room using standardized reference curves.
WEIGHTED STANDARDIZED LEVEL DIFFERENCE (DnT,w):
Average level difference between rooms, corrected for reverberation, to assess airborne sound insulation.
WHITE NOISE:
Random broadband noise with constant power across frequencies. More energy at higher frequencies; sounds like hissing.
DASM – Vietnam’s pioneer in acoustic testing, noise measurement & consulting
With a team of expert engineers and acousticians, equipped with internationally standardized equipment, DASM offers professional acoustic services and comprehensive testing–analysis–design consulting solutions for all types of buildings.
DASM acoustic services include:
- On-site acoustic testing and measurements: noise, reverberation, impact sound (ISO, TCVN, BS EN standards)
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- Acoustic design consulting for: auditoriums, theaters, studios, factories, offices, hospitals, schools, etc.
From cultural spaces to industrial facilities, DASM has supported hundreds of clients in creating optimal, safe, and sustainable acoustic environments for every kind of project.
Contact DASM today for specialized acoustic solutions—right here in Vietnam, to international standards.
