Airborne and Impact Noise

Airborne and impact noise are the two fundamental categories of sound transmission in buildings — and solving them requires completely different approaches. Misidentifying your noise problem leads to wasted money and disappointing results. This guide gives you the technical knowledge to correctly diagnose your noise issue, understand the physics behind it, and select the right acoustic products and systems to resolve it — including full compliance guidance for UK Building Regulations Part E.

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What Is Airborne Noise?

Airborne noise is sound that originates as pressure waves in air. Common sources include:

• Conversation and voices from neighbours or adjacent rooms
• Music, television, and home entertainment systems
• Traffic noise entering through external walls or windows
• HVAC and mechanical plant noise
• Barking dogs, alarms, and general environmental noise

Airborne sound waves strike a partition (wall, floor, or ceiling) and cause it to vibrate, re-radiating sound energy on the other side. The resistance of a partition to airborne sound is primarily determined by its mass — the heavier and denser the element, the less it vibrates in response to incident sound pressure, and the less energy is transmitted.

This relationship is described by the Mass Law: doubling the mass of a partition increases its sound reduction index (Rw) by approximately 6 dB. A solid 215mm brick wall achieves approximately Rw 48–53 dB; a 100mm stud wall with single plasterboard achieves only Rw 33–38 dB. The difference — 15–20 dB — represents a dramatic difference in perceived noise level.

What Is Impact Noise?

Impact noise is generated by physical contact between objects and building structure — the energy is introduced directly into the structure as vibration, rather than via air. Common sources include:

• Footsteps on a hard floor above (the single most common noise complaint in UK flats)
• Dropped objects, furniture dragging, children running
• Mechanical vibration from washing machines, pumps, and plant
• Slamming doors and structural knocks

Impact noise is structurally transmitted — it bypasses the air gap that helps reduce airborne noise. A thick concrete floor (excellent at blocking airborne sound) transmits impact energy extremely efficiently because concrete is rigid and has very low internal damping. Mass alone does not solve impact noise — decoupling and resilience are required.

How the Two Noise Types Require Different Solutions

The Physics of Sound Transmission

Mass Law (Airborne)

The Mass Law governs airborne sound transmission through a single-leaf partition. For a surface mass density (m, in kg/m²):

Rw ≈ 20 log(m × f) − 47 dB

Where f is frequency (Hz). In simplified terms, for every doubling of mass, Rw improves by ~6 dB. This is why adding a second layer of plasterboard (from 12.5mm to 25mm) adds approximately 3–5 dB — you've doubled the plasterboard mass, not the total wall mass. The additional mass of the mineral wool, air cavity, and substrate also contribute.

At frequencies above the critical frequency of the partition (where bending waves in the plate match the incident sound wavelength), transmission increases significantly — this is the coincidence dip, and it's why single-leaf construction has inherent limitations even at high mass levels.

Decoupling and the Double-Leaf Principle

Double-leaf construction — two separate leaves with an air gap between them — can dramatically outperform a single leaf of equivalent mass. The air gap decouples the two leaves, so vibration from one leaf is not directly transferred to the other. A 100mm air gap between two 12.5mm plasterboard leaves with 50mm mineral wool can achieve Rw 48–52 dB — comparable to a 300mm solid concrete wall.

The key requirement is that the two leaves must not be rigidly connected. Any direct rigid connector (metal tie, plasterboard screw touching both leaves, pipe, cable without isolation) creates a sound bridge that short-circuits the isolation and dramatically reduces performance. A single sound bridge can reduce DnT,w by 10–15 dB.

The Critical Difference for Floors

A concrete separating floor between flats will typically achieve DnT,w 52–56 dB (excellent for airborne noise). However, the same floor will achieve LnT,w 75–80 dB (extremely poor for impact noise) because concrete is rigid and transmits structural vibration efficiently. The solution requires a floating element — a layer of resilient material between the structure and the floor finish. This is why footstep noise is the most common acoustic complaint in UK flats built without a floating floor.

Performance Standards & Measurement

Airborne Sound Measurements

• Rw (Weighted Sound Reduction Index): Laboratory measurement. Standardised test conditions. Used for product ratings and system design.
• DnT,w (Weighted Standardised Level Difference): Field measurement. Accounts for room size, reverberation, and flanking. Part E uses DnT,w. Typically 2–8 dB lower than Rw for the same construction due to flanking.
• STC (Sound Transmission Class): North American equivalent of Rw. Numerically very similar to Rw for most constructions.

Impact Sound Measurements

• Ln,w (Weighted Normalised Impact Sound Pressure Level): Laboratory measurement. Lower value = better performance.
• LnT,w (Weighted Standardised Impact Sound Pressure Level): Field measurement, accounts for reverberation. Used in Part E. Lower = better.
• ΔLw (Weighted Impact Sound Improvement): The improvement provided by an overlay (floor covering, underlay) compared to the bare structural floor. Higher = better. Used to characterise acoustic underlays and floor coverings.
• IIC (Impact Isolation Class): North American equivalent. IIC = 110 − Ln,w (approximately). IIC 50+ is considered adequate for residential; IIC 60+ is high performance.

Part E Requirements (England & Wales)

Application Guide — Solutions by Scenario

Scenario 1: I Can Hear My Neighbours Talking Through the Wall

This is airborne noise through a separating wall. The wall has insufficient mass and/or is flanking around the party wall via connected structure. Solution:

• Build an independent stud wall 25–50mm clear of the party wall
• Fill with 75–100mm acoustic mineral wool (minimum 45 kg/m³)
• Finish with double 12.5mm plasterboard on resilient bars or isolation clips
• Seal all perimeter gaps with acoustic sealant
• Expected result: DnT,w improvement of 8–18 dB, achieving 50+ dB in most cases

Scenario 2: I Can Hear Every Footstep from Upstairs

This is impact noise through a separating floor. Unless you have access to the floor above to install a floating floor, the most practical retrofit is a resilient ceiling system below. Solution:

• Fix resilient bars or isolation clips to existing ceiling at 400mm centres
• Fill joist bays with 100mm acoustic mineral wool
• Hang double 12.5mm plasterboard on resilient bars (do not direct-screw through bars to structure)
• Seal all perimeter gaps
• Expected result: LnT,w improvement of 12–20 dB; DnT,w improvement of 8–15 dB

Ideal solution is to also add acoustic underlay on the floor above — even a 6mm acoustic mat or cork underlay adds ΔLw 14–22 dB above the structural floor.

Scenario 3: Music and Bass Coming Through the Floor/Ceiling

Low-frequency airborne noise (bass, subwoofer) requires mass plus decoupling. Standard resilient bar systems are less effective at low frequencies (<100 Hz). For genuine bass control:

• Independent ceiling (room-within-room) with 150–200mm air gap
• Acoustic mass panels (acoustic plasterboard + MLV composite)
• Low-frequency resonant panel absorbers inside the space
• Full decoupling of ceiling — no rigid contact to structure

Scenario 4: Traffic and External Noise Through Walls

External noise entering through walls is airborne. The primary paths are: (1) the wall itself, (2) windows, (3) ventilation gaps. A well-insulated external wall (cavity masonry, insulated stud) typically achieves Rw 45–55 dB. Acoustic windows and ventilators can achieve Rw 40–48 dB. Improving the weakest link (usually windows or ventilation) gives the greatest benefit.

Scenario 5: New Build Flat — Meeting Part E

Both airborne and impact requirements must be met simultaneously. Use a Robust Detail-compliant system: for concrete floors, 150mm+ slab + under-screed acoustic rubber membrane (6mm minimum) + 65mm+ floating screed + appropriate floor finish. For walls, 215mm blockwork + independent lining on both sides. See our Sound Reduction Systems collection for complete system details.

Product Selection Guide

For Airborne Noise:

• Acoustic mineral wool (45–60 kg/m³): Cavity fill in walls and between joists. Rw uplift 4–10 dB in system.
• Mass Loaded Vinyl (5 kg/m²): Barrier layer in walls or ceilings. Standalone Rw ~27–29 dB.
• Acoustic plasterboard (12.5–15mm): Higher mass than standard board, better mid-frequency performance.
• Double plasterboard layers: Second layer adds 3–5 dB; staggered joints and resilient mounting multiplies the gain.

For Impact Noise:

• Acoustic rubber underlay (6–15mm): ΔLw 17–27 dB under floating screed or floor boarding.
• Cork acoustic underlay (3–10mm): ΔLw 14–20 dB, sustainable, excellent under hard flooring.
• Resilient bar system: LnT,w improvement 10–15 dB for ceiling below existing timber floor.
• Isolation clip system: LnT,w improvement 15–20 dB; more effective than bars, more expensive.

Frequently Asked Questions

How do I know if my problem is airborne or impact noise?

The simplest test: if you can hear noise through the wall or floor when the neighbour is just talking, playing music, or watching TV at normal volume — that's primarily airborne. If the noise is clearly footsteps, thuds, or scraping — that's primarily impact. Many real-world situations are mixed. A pre-existing hard floor without any soft covering above you is almost always an impact noise problem.

Can one product solve both airborne and impact noise?

Some products address both, but usually with different emphases. A floating floor system (resilient layer + floating screed) primarily solves impact noise but also improves airborne performance through the added mass of the screed. Acoustic mineral wool primarily improves airborne performance but also helps dampen resonance in floor cavities. The best results always come from systems that target both mechanisms specifically.

Why does my upstairs neighbour's footsteps sound so loud if I have carpets?

Carpet with underlay provides significant impact noise reduction on the same floor (ΔLw typically 20–35 dB for a thick carpet) — but this benefit is yours as the person below only if the carpet is on the floor above you. Your own carpet in your flat reduces noise you generate, not noise from above. The structural floor between you and your neighbour is what needs treatment.

Is it possible to completely soundproof against airborne noise?

Complete soundproofing is not practically achievable in most building structures without extremely expensive room-within-room construction. However, 45–55 dB of isolation (achievable with good system design) means that a neighbour's TV at normal listening volume (60–65 dB) would be inaudible or barely perceptible through the partition. For most residential situations, 45–50 dB isolation is transformative.

Does acoustic insulation help with noise from a street or external source?

Yes, but external noise enters via multiple paths — wall, windows, roof, ventilation. Improving the wall without upgrading windows may show little improvement if windows are the dominant path. Assess all noise paths before specifying — our acoustic team can help with diagnosis.

What is flanking noise and why does it matter?

Flanking noise is sound that bypasses the directly treated element by travelling through connected structure. For example, sound travelling from a flat through the party wall, through the floor, and re-radiating into the room below — bypassing even an excellent ceiling treatment. Flanking is the main reason field-measured DnT,w is typically 2–8 dB below the laboratory Rw prediction. Effective soundproofing addresses both direct and flanking paths.

How much noise reduction can I realistically expect?

With professional-grade products correctly installed, a typical residential retrofit can achieve: 8–15 dB reduction from a resilient ceiling bar system; 10–18 dB from an independent wall lining; 12–20 dB from a floating floor addition. Total perceived noise volume is halved for every 10 dB reduction. A 15 dB improvement is typically transformative for occupant comfort.

Do I need a sound test to sell or rent my property?

For new-build dwellings and material change of use (e.g., house to flats), pre-completion acoustic testing is required unless Robust Details are used. For existing properties being sold or rented, no mandatory acoustic testing is required. However, if you've carried out building work that required Building Regulations approval, the work must comply with Part E.

Why Sound Deadening UK?

• Expert diagnosis support: Not sure whether your problem is airborne or impact? Our acoustic team can help you identify the right solution before you spend money on the wrong product
• Full product range for both noise types: Airborne barrier materials, impact resilient layers, complete systems — all from one supplier
• UK stock and fast delivery: All products available for next-day delivery to mainland UK
• Real performance data: Every product listed with laboratory-tested DnT,w, ΔLw, or Rw data — not marketing estimates
• Trade and contractor pricing: Volume discounts for regular buyers; credit accounts available

Not sure which noise type you're dealing with? Contact our acoustic team — we'll help you diagnose the problem and select the right solution.

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