Noise within buildings can travel through air or through structure. These two types — airborne noise and impact noise — behave very differently and require specific design approaches. Knowing the difference is the first step toward effective sound control.
1. Airborne noise: vibration through the air
Airborne noise is transmitted through air as pressure waves: speech, music, traffic, HVAC systems, or office equipment. When these waves hit walls or floors, they cause them to vibrate and re-radiate sound. To limit this, acoustic insulation is essential. Dense, airtight, and decoupled partitions are key to stopping airborne transmission.
2. Impact noise: vibration through the structure
Impact noise results from direct contact with the structure — footsteps, furniture movement, dropped objects. The vibration travels through solid elements such as concrete, steel, or wood before being heard in other rooms. It often produces dull, low-frequency sounds.
Reducing impact noise involves mechanical decoupling: floating floors, resilient layers, or suspended ceilings that interrupt vibration paths.
3. Measuring and differentiating both types
Acoustic diagnostics rely on two standardized indices:
- Rw (Sound Reduction Index) — rates resistance to airborne noise (the higher, the better).
- L’nT,w (Normalized Impact Sound Level) — measures structure-borne sound (the lower, the better).
Both are measured in decibels (dB) and define a building’s overall acoustic comfort level.
4. When to address airborne or impact noise
In offices, restaurants, or housing, both types often coexist. - Airborne noise dominates when voices or music cause discomfort. - Impact noise is the issue when footsteps or furniture vibrations are heard between floors.
5. Best design practices
- Design double walls or floors with separate layers to reduce transmission.
- Ensure airtight construction — air leaks are sound leaks.
- Use resilient mountings to avoid rigid connections between materials.
- Complement insulation with sound absorption to control reverberation within rooms.
6. Balancing isolation and absorption
True acoustic comfort combines isolation (blocking sound transmission) and absorption (reducing echo and reverberation). Both must work together to create calm and intelligible environments.
FAQ
What is the difference between impact and airborne noise?
Airborne noise travels through air (speech, music), while impact noise is transmitted through the building’s structure (footsteps, shocks).
Can impact noise be completely eliminated?
No, but it can be greatly reduced through mechanical decoupling and vibration control design.
How does material density affect noise control?
High-density materials block airborne noise effectively, while impact noise reduction relies on structural decoupling rather than mass.
How is acoustic performance verified?
Rw and L’nT,w measurements, carried out by an acoustic engineer, provide quantitative data on sound insulation performance.