Acoustic comfort is a valuable and important aspect in buildings. That is why acoustic consulting, acoustic consulting and design, and sound insulation within building structures are essential to ensure the isolation or complete reduction of airborne sound and structure-borne sound. Let’s explore all the necessary information about these two types of sound with DASM in the article below.
What is sound?
Sound is a general term that refers to mechanical vibrations in an elastic medium, which can be gas, liquid, or solid. These vibrations propagate through the medium as sound waves. In the air, sound waves are fluctuations in pressure and density.
In everyday terms, sound is what we perceive through our auditory system – including the ears and the brain. Useful sound is the kind of sound we find pleasant, such as music or voices in conversation. In contrast, noise – like the sound of traffic or construction sites – is often perceived as annoying or disturbing.
What’s the difference between airborne sound and structure-borne sound?
Sound becomes noise when it causes disruption, stress, or harm to the environment. Most often, the reason sound is perceived as noise is due to its volume.
Whether a sound is considered noise or not largely depends on the listener’s perception. Noise can disrupt sleep patterns, reduce concentration, and interfere with rest. Even though our bodies may adapt over time, prolonged exposure can have negative effects on both physical and mental health.
Direct sound
Direct sound is the first sound that reaches the listener’s ear in an enclosed space – meaning it hasn’t been reflected. Ambient or diffuse sound travels indirectly, bouncing off surfaces before reaching the ear.
Direct sound helps us determine the direction of the sound source, while reflected sound contributes to the reverberation or clarity in a space. For example, if the delay between direct and reflected sound is about 30 milliseconds, listeners may feel as if they’re in a large room.
Structure-borne sound and airborne noise can transform into each other at the boundary between solid and air.
Types of sound
When a solid material (like a wall) is excited by a sound wave, it’s called structure-borne sound. In contrast, when air is excited, it’s airborne sound.
These two types of sound can convert into each other at the interface between air and a solid object. Air-transmitted sound travels around 330 m/s, while in concrete it can travel up to 3,400 m/s – about 10 times faster.
What is structure-borne sound?
Structure-borne sound travels through walls, floors, or other solid materials and can be generated in several ways:
• Direct structure-borne sound: Caused by direct mechanical impact – such as drilling into a wall. Impact sound, like footsteps, falls into this category.
• Indirect structure-borne sound: Occurs when Air-transmitted sound is strong enough to make solid objects vibrate.
We don’t hear structure-borne sound directly, but we can feel it – like strong bass vibrations from techno music. In order for the ear to perceive it, structure-borne sound must first be converted back into airborne sound at the surface.
How to measure structure-borne sound?
Using a structure-borne sound transducer, which converts mechanical vibration into an analog electrical signal. Common parameters measured include:
• Displacement amplitude
• Vibration velocity
• Vibration acceleration
How to reduce structure-borne sound?
Reducing structure-borne sound is challenging, as it travels through hard materials like walls, ceilings, and floors. But here are highly effective methods:
1. Decoupling the structure
Use isolating materials between structural parts to prevent vibration transfer.
Examples:
• Rubber pads, acoustic foam, or suspended ceilings with isolation hangers
• Double stud walls (independent wall frames on each side, not touching)
2. Damping layers
Install damping membranes or anti-vibration mats between two rigid layers (e.g., gypsum boards).
They absorb vibration energy, reducing transmitted sound.
3. Adding mass
Heavier materials transmit less sound.
Options:
• Add extra layers of drywall, cement board, or specialized soundproofing panels
• Use heavy masonry or concrete walls where possible
4. Isolating mechanical systems
Pipes, HVAC systems, and fans often cause vibration.
Solutions:
• Use flexible joints, acoustic sealants, or suspended mounts
• Avoid direct contact between systems and the structure
5. Prevent flanking paths
Structure noise can “sneak” around via small openings like ducts, door gaps, or electrical conduits.
Solutions:
• Seal all gaps using acoustic sealant
• Use acoustic doors and seal wall penetrations properly
6. Isolate floors and ceilings
If noise travels through floors or ceilings:
• Use floating floors with isolating layers
• Install suspended ceilings with resilient hangers or springs
• Avoid mounting subwoofers to walls or floors
To effectively treat structure-borne noise, combine isolation, mass increase, and vibration damping. Especially during the design phase of a project, it’s essential to plan for potential noise issues to optimize cost and performance from the start.
What is airborne sound?
Airborne sound – or airborne noise – is sound that travels through the air from a source as a sound wave. Human ears can hear sounds in the 20–20,000 Hz range.
How to measure airborne sound?
Use the unit decibel (dB) to express sound pressure level.
• 0 dB = quietest audible sound
• 140 dB = pain threshold
• The scale is logarithmic: +10 dB sounds twice as loud
dB(A) is a frequency-weighted scale that reflects how the human ear perceives loudness (less sensitivity to low frequencies).
How to reduce airborne noise?
Rely on sound absorption:
• Soft, porous materials absorb sound better than hard, reflective surfaces
• Thick, heavy walls (brick, concrete, stone) block sound more effectively
• For lightweight walls, consider building a second, separated layer
• Avoid gaps or holes that could reduce sound insulation
Sound absorption materials are rated from Class A to E:
• Class A: Absorption coefficient 0.9–1.0 (very high absorption)
• Class E: 0.15–0.25 (low absorption)
The key difference between airborne and structure-borne sound
The main difference is the transmission medium:
• Airborne noise travels through air
• Structure-borne noise travels through solids (stone, concrete, wood, etc.)
Examples of structure-borne noise include footsteps or machinery in a building.
Structure-borne sound can convert into airborne noise when it reaches a surface – only then can the ear detect it.
Professional Acoustic Solutions from DASM
DASM Institute, equipped with modern tools, can help you survey, evaluate, and advise on the best acoustic solutions for your building’s noise problems.
Right from the design phase, acoustic analysis should be included. Identifying the type of sound and choosing the right treatment is the key to minimizing airborne and structure-borne noise, providing a peaceful, high-quality living and working space.
DASM is always ready to support businesses, architects, and engineers in managing sound, vibration, and shock in construction projects.
👉 Contact DASM Institute now for professional acoustic consulting and optimal acoustic solutions tailored to your project!
