LuoFu will provide you with an in-depth explanation of the actual noise reduction achieved by noise barriers on-site, including the principles behind the measurement of IL (Insertion Loss) according to international standards and the actual noise reduction values.
I. What Is the Insertion Loss (IL) of a Noise Barrier?
In all international highway standards, including ISO 10847, EN 1793-4, and those of the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO), Insertion Loss (IL) is the final and sole on-site acceptance criterion for evaluating the noise reduction effectiveness of noise barriers.
Formula for calculating Insertion Loss (IL):
IL = L1 (original noise level without the noise barrier) − L2 (noise level after installing the noise barrier)
The unit is uniformly dB(A) (A-weighted, reflecting the actual weighting characteristics of human hearing).
The Core Logic of International Trade:
The STC, DLR, and Rw ratings of sound barriers represent “laboratory sound insulation performance,” which merely indicate that the material can block sound transmission; whereas Insertion Loss (IL) represents the actual noise reduction benefits that residents, buildings, environmental impact assessments, and property owners can realistically expect.
Industry Rule of Thumb (Mandatory Requirement for Overseas Bids):
The sound insulation performance of a noise barrier must exceed the on-site IL value by at least 10 dB. If the difference is insufficient, noise will seep through, rendering the on-site noise reduction ineffective.
II. Why Is the Actual Noise Reduction Achieved by IL Always Lower Than the Sound Insulation Rating of Sound Barriers? This Is Also the Biggest Misconception Among Customers
Many customers ask: If a sound barrier can block 30 dB or 35 dB of noise, why is the actual noise reduction on-site only 10–20 dB?
This is because outdoor noise has three paths to bypass the sound barrier, which differ from conditions in a laboratory environment:
1. Overhead diffraction (accounting for 70% of noise reduction loss): Most noise does not penetrate the barrier panels but instead passes over the top of the barrier and spreads into residential areas.
2. Diffraction at the sides of the noise barrier (accounting for 20% of noise reduction loss): When the barrier is not long enough or there are gaps at both ends, sound waves bypass the barrier directly from both sides.
3. Superposition of reflections from the ground and buildings (accounting for 10% of noise reduction loss): Secondary noise reflected from road surfaces and walls increases the background noise level.
Therefore, no matter how high-quality the panels are, they only serve to control “transmitted noise”;
the on-site effectiveness of IL is primarily determined by diffraction.
III. “Actual IL Noise Reduction Range” for Different Barrier Structures Under International Standards
The following values are based on field measurements conducted under standard conditions in accordance with ISO 10847 (level roadbed, no significant elevation differences, standard traffic volume, and measurement points located at low-rise sensitive buildings adjacent to the road). These values are commonly used as standard references in overseas quotations, design proposals, and environmental impact assessment reports.
1) Low Barriers: 2.0–3.0 meters (Pure Sound Insulation / Standard Highway Model)
Actual IL Value: 5–12 dB(A)
Applications: Township roads, service roads, and low-traffic roads
Characteristics: Blocks the line of sight only at the lower section; extremely strong diffraction effects at the top
Human Perception: Noise becomes muffled and less piercing, but the environment does not become noticeably quieter
2) Standard upright noise barriers: 3.5–5 m, also the mainstream model for highways worldwide
Actual Insulation Level (IL): 12–20 dB(A)
Applications: Urban highways, intercity highways, and most overseas municipal projects
Structure: Micro-perforated panels + high-density acoustic foam, effectively eliminating road surface reflection noise
Human Perception: Noise reduction is very significant; grating tire noise is almost completely eliminated; and it is possible to carry on normal conversations and sleep inside the vehicle.
International Statistics: In 80% of global highway projects, the final accepted IL values fall within the range of 14–18 dB, representing a standard of high-quality results.
3) Elevated and irregular-shaped roof barriers 6 meters and above, including curved, T-shaped, and angle-optimized noise-reduction enhanced models
Actual IL Value: 20–25 dB(A)
Application Scenarios: Elevated road embankments, raised road surfaces, high-rise residential areas, and densely populated residential zones
Principle: The elevated design expands the acoustic shadow zone; the specialized roof structure disperses diffracted sound waves
Human Perception: Significantly suppresses traffic roar; noise levels during both day and night easily meet European and American residential standards
4) Fully Enclosed Sound Barrier (Full Sound Enclosure)
Actual Insulation Level (IL): 22–28 dB(A)
The only solution capable of simultaneously blocking structure-borne noise, top-side diffraction noise, side-diffraction noise, and reflected noise
A top-tier solution specifically designed for urban core areas, elevated roads with dense building clusters, and airport expressways
IV. Human Perception Levels
dB(A) is the unit of measurement for noise levels; for every 10 dB reduction, the noise perceived by the human ear is halved:
IL 5–10 dB: Slight improvement; the harshness is somewhat reduced, but the overall noise remains
IL 10–15 dB: Significant noise reduction; comfort in daily life is significantly improved, meeting municipal standards
IL 15–20 dB: High-quality noise reduction; traffic noise no longer interferes with daily life, meeting the top standards for projects in Europe and the United States
IL 20 dB+: Ultimate noise reduction; outdoor traffic noise is essentially reduced to low-level background noise
V. Why Does the On-Site Sound Level Index (IL) of the Same Noise Barrier Fluctuate, Varying Between High and Low Values?
For the same 4-meter-high metal sound-absorbing barrier, why is the sound insulation index (IL) measured at some construction sites 18 dB, while at others it is only 12 dB? The international engineering community generally recognizes the following five variables:
1. Line-of-sight obstruction has the greatest impact: When the barrier completely blocks the line of sight to the sound source, the sound insulation index (IL) is higher; when the line of sight is unobstructed and traffic conditions are visible, the noise reduction effect is significantly reduced.
2. Distance from the measurement point: 0–50 meters: optimal performance; >60 meters: attenuation within the acoustic shadow zone causes the IL to automatically decrease by 3–8 dB.
3. Difference in floor height: 1–3 low-rise floors: adequate noise reduction; 4 or more high-rise floors: gradually moving out of the acoustic shadow zone; IL decreases as the number of floors increases.
4. Traffic type: High-frequency noise from passenger cars: higher IL; low-frequency noise from heavy trucks: significant diffraction effects, resulting in a lower IL.
5. Barrier Integrity: Gaps, expansion joints, gaps between columns, and insufficient end caps—each of these directly reduces noise reduction effectiveness by 5–10 dB.
VI. International Noise Level (IL) Acceptance Criteria
EU EN + ISO 10847: General residential areas—IL ≥ 10 dB(A); Sensitive areas (schools/hospitals)—IL ≥ 15 dB(A)
U.S. Federal Highway Administration (FHWA)/American Association of State Highway and Transportation Officials (AASHTO): Compliance requires IL ≥ 10–15 dB; 15 dB+ indicates a high-performance noise reduction solution
The laboratory sound insulation values of noise barriers represent the upper limit of the product’s inherent quality, while the insertion loss (IL) reflects the actual noise reduction achieved by the customer after final installation. In actual industry projects: conventional highway noise barriers can consistently reduce noise by 12–20 dB(A); elevated and irregularly shaped barriers can achieve 20–25 dB(A); and fully enclosed structures can reach up to 28 dB(A). The key limiting factor for insertion loss (IL) is not the sound insulation performance of the panels themselves, but rather diffraction control, barrier height, on-site elevation differences, and the integrity of the installation—which is precisely the main distinction between professional noise barrier projects and ordinary construction fencing.