Flanking is the transfer of noise through paths around a building element, rather than through the building element itself. Flanking can describe the transfer of noise through: gaps and cracks in a building element; incorrectly sealed junctions between two materials; or other indirect paths such as air conditioning ducts or ceiling cavities. These noise flanking paths can defeat noise reduction techniques.
All sounds can be described by their frequency or their mix of frequencies. Sounds have a mix of frequencies that are particular to the nature of the sound. Frequency can be measured on a scale in units of Hertz (Hz). Higher frequency sound is generated by sources such as tire squeals or speech. Low frequency sound is generated by sources such as music subwoofers or truck engines. Low frequency sound is more difficult to control or reduce than high frequency sound and requires specialised design and construction.
Impact noise is caused by impact or collision on the walls or floor of an adjoining room. Typical sources of impact noise are footsteps on the floor above a residence, washing machines and dryers that are incorrectly mounted to a wall and slamming doors on cupboards mounted on a common wall.
Sound insulation refers to the ability of a material to stop or reduce airborne sound. High mass, dense and well sealed materials generally offer improved sound insulation. Internal sound insulation is important when designing a wall (or other partition) to stop noise passing through from an adjoining room. External sound insulation refers to the ability of materials to reduce sound transmitting into or from a building. Good external sound insulation is important when designing and constructing the external elements of a building. This includes walls, windows, doors, ventilation and roofing.
The decibel (dB) is the unit used for sound level measurement. Variations of the dB are used for different types of noise measurement. The most commonly used variation is the dBA.
Unit of sound level, in A weighted decibels. The human ear is not equally sensitive to all frequencies of sound. The A weighting approximates the sensitivity of the human ear by filtering these frequencies. A dBA measurement is considered representative of average human hearing.
Referred to as the Weighted Standardised Field Level Difference, DnT,w is a measure of the sound insulation performance of a building element that indicates the level of speech privacy between spaces. It is characterised by the difference in noise level on each side of a wall or floor. Measured in the field, DnT,w is subject to the inherent inaccuracies involved in such a measurement. . It is a field measurement that relates to the R w laboratory measurement. The higher the number, the better the insulation performance.
Referred to as Weighted Standardised Field Impact Sound Pressure Level, L’nT,w is a measure of the noise impact performance of a floor. It is a field measure of the amount of impact sound reaching a space via a floor. L’nT,w is characterised by how much sound reaches the receiving room from a standard tapping machine. It is measured in the field and is therefore subject to the inherent inaccuracies involved in such a measurement. It is the equivalent field measurement to the L’n,w laboratory measurement. The lower the number, the better the performance.
Known as the Weighted Sound Reduction Index, R w is a single number (dB) referring to the ability of a wall or other building structure to provide sound insulation. The higher the number, the better the sound insulation. R w refers to sound insulation achieved in an acoustic testing laboratory.
Rw + C tr
This measure is the same as R w but includes an adaptation factor (C tr ) to take into account low frequency sounds generated by home theatre and sound system equipment. The adaptation factor is a negative number and therefore R w + C tr is lower than R w.
Loudness is a subjective term describing the strength of the ear’s perception of a sound.
The ability of a building component to diminish the intensity of vibration energy passing through it, and to minimise any vibration being transmitted to a connected element. It is analogous to the absorption of sound in air.
Anti vibration pads are used as damping between building elements. This term refers to any connecting device that provides some level of resilience between components such as rubber or damping springs.
Vibration control materials are also used when installing an isolated building component such as a floating floor, stairs or suspended ceiling. They can also be used when underneath devices such as air conditioners, heating systems and chillers.