Types of Sound Transmission
Put very simply, sound is a form of energy produced when a material vibrates. For example, when you flick the rim of a glass, the glass will vibrate imperceptibly. These vibrations move through the air and strike the ear drum of anyone within hearing range (click here to find out ‘How Our Ears Hear’).
In fact, these vibrations, or sound waves, can move through any medium: gas, liquid or solid. Robert Boyle, the 17th Century chemist and physicist, conducted an experiment using a ringing bell, a bell jar and a vacuum pump to demonstrate that sound requires a medium through which to move and can’t be transmitted through a vacuum.
A Little About Waves
The type of wave we are most familiar with is the kind we encounter at the seaside. This is a ‘transverse’ wave. The vibration moves up and down, while the wave moves forward. A sound wave is a ‘longitudinal’ wave. In this type of wave, the vibration moves in the same direction the wave travels.
Sound waves that move through the air are, unsurprisingly, described as ‘airborne’. Examples of airborne sound include:
- Sound coming from a radio or television
- A barking dog
A sound wave that moves through a solid medium is known as ‘impact’ sound. Examples of impact sound include:
- Footsteps on a hard floor
- A slamming door
- Rapping on a window
Although impact sound travels through a solid medium, at some point it emerges and is experienced as airborne noise. So, if the person in the apartment above jumps up and down on their laminate floor while wearing clogs, impact sound is going to move through the materials of their floor and your ceiling. But, in short order, it emerges from your ceiling and travels down to your ear as airborne sound. Similarly, airborne sound can strike a solid medium (for example, a steel beam) and, thereafter, travels through that medium as impact sound. It then re-emerges as airborne sound in, say, an adjacent room. This phenomenon is known as ‘flanking’.
Treating Airborne Sound
The most effective way of reducing the transmission of airborne noise is to block the sound with dense, high-mass materials. Here at Akoustix, we have number of solutions that are highly effective at treating airborne sound, including Karma Soundlay Highload 15 acoustic barrier (which includes two layers of weight-enhanced, high-density material) and Karma Acoustic Overlay 23 (which includes a high-mass flooring grade (P5) chipboard.
The most effective soundproofing solutions to treat airborne noise comprise combinations of materials (overlay boards, acoustic barriers and dense plasterboard such as Gypsum Soundbloc) to create a noise attenuating system.
Treating Impact Sound
The most effective solutions for dealing with impact noise aren’t hard and dense; they are softer ‘resilient’ materials that absorb the impact vibrations. Carpet, for example, can help reduce impact noise. Materials that are effective at reducing impact noise include Regupol® 3912 Acoustic Underlay (comprised of a soft PUR foam) and Karma Acoustic Joist Hoods (ideal for loft conversions).
It’s worth mentioning that if, for example, you have a noisy neighbour living above you, you’re likely to be suffering as a result of both impact and airborne noise (e.g. their clog dancing and their appalling taste in music). So, an airborne-and-impact-noise acoustic solution, comprising both dense and soft materials, is called for.
Treating Flanking Noise Transmission
The most effective solution to the typical flanking problem of noise transmission through a wall (bypassing an otherwise effectively treated floor) is the use of flanking strips sometimes called perimeter strips and frequently produced from materials like rubber crumb. These strips effectively isolate the wall (timber/metal studwork or blockwork) from the floor.
- Soundwaves are vibrations that move through a solid, liquid or gas medium
- Airborne sound moves through the air (e.g. a dog barking)
- Impact sound moves through as solid (e.g. footfalls on a floor)
- Flanking is sound that circumvents an acoustic solution by finding another route (e.g. compromising an acoustic floor by infiltrating through a wall)
- Airborne noise is best treated with dense, high-mass materials (e.g. weight-enhanced barriers)
- Impact noise is best treated with softer, absorbent materials (e.g. rubber crumb, PUR foam or cork)
- Flanking noise is best treated with isolating materials (e.g. rubber-based flanking strips)
- The best solutions tend to be acoustic systems which tackle airborne, impact and flanking noise problems