We have provided a list of Acoustic Terms that you will come across in regards to Acoustics, Sound Insulating and Sound Absorption.


  • Absorption Coefficient

Absorption Coefficient is the measurement of how much of a particular wave length is absorbed into a material

  • Airborne Sound

Airborne Sound consists of sound waves travelling through the air, e.g TV, Music, Speech.

  • Ambient Noise

Ambient noise is the background noise of any given location, this excludes the noise source e.g. with traffic noise, the background noise would be measured with no traffic and would gather information of the ambient noise of the room.

  • Attenuation (dB)

Attenuation is lowering the overall dB level from the noise source.

  • Building Regulations Part E

Building Regulations Part E is a government document addressing sound issues within new builds, specifying a requirement for high performance partitioning against sound transmission from room to room. (http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_E_2010.pdf)

  • dB(A)

dB(A) is a measurement of sound using the A-weighing scale, which is set to simulate the human hearing response – it has now become the standard measurement for dB.

  • Flanking Transmission

Flanking transmission consists of the various paths sound can travel into a receiving room, for example, it could pass through joists and cavities in the floor, ceiling and wall. It can also be heard in chimney breasts which can reverberate into the a-joining rooms as it travels up and down the chimney. [See Fig.1 for a diagram showing this]

  • Frequency

Frequency consists of the number of cycles per second. This is expressed in Hertz (Hz) Kilohertz (Khz) in regards to acoustics.

  • Impact Sound

Impact Sound consists of a transference of sound energy onto a surface, e.g someone walking on the floor above. [See Fig.2 for a diagram showing this]

  • Mass Law

Mass Law theory explains that a doubling of density will result in a 6dB decrease.

  • Sound Absorption

The control of sound in a room and absorb reflections to reduce an RT60 or, for example, in a recording studio, it would be used to control Early reflections, in a theatre hall, it would be used to control Late reflections

  • Sound Insulation

The method used to keep sound from transferring to a-joining spaces. The use of various methods to insulate the sound is adopted here, for example, rock wool used between wall cavities.

  • Sound Transmission

Sound Transmission is a sound wave passing through any given medium that transfers from source to receiving.

  • Vibration

Vibration is an oscillation in both structural and airborne, usually unwanted in the case of structures. E.g. Train motion in a nearby railway causing vibrations within the structure.



Dn : Normalized Level Difference (Airborne)

DnT : Standardized Level Difference (Airborne)

DnT,w : Weighted Standardized Field Level Difference (Airborne) - Field measurement standardized to 0.5 second reverberation time, results will include flanking

DnT,w + Ctr : Weighted Standardized Level Difference with Spectrum Adaption Term Ctr (Correction) (Airborne) - Associated with a single number quantity on a field measurement (with correction)

LnT : Standardized Impact Sound Pressure Level (Impact)

L'nT : Standardized Impact Sound Pressure Level (Impact)

LnT,w : Weighted Standardized Impact Sound Pressure Level (Impact) - Associated with a single number quantity on a laboratory measurement

L'nT,w : Weighted Standardized Impact Sound Pressure Level (Impact) - Associated with a single number quantity on a field measurement



  • Early Reflections

The Early Reflections in reverberation are the first reflections off nearby surfaces heard after the source sound. [See Fig.3 for a diagram showing this]

  • Late Reflections

Late reflections are sounds that are heard as a delay are considered late reflections, these build up to create reverberation. [See Fig.3 for a diagram showing this]

  • Reverberation

Reverberation is the decay of sound after the source is emitted and consists of Early and Late reflections. [See Fig.4 for a diagram showing this]

  • Reverberation Time

This is the length of time after the source sound that takes to decay, this would often be measured with an RT60 measurement.

  • RT60

RT60 is a measurement of reverberation time, it starts with the original signal noise and is calculated by the duration of the decay to reach 60dB. In smaller spaces, or where it is not possible to achieve an RT60, an RT30 or RT20 may be used. This is measured in seconds.

  • Speech Intelligibility

Speech Intelligibility is the clarity of speech, how well the source speaker can be heard and understood in a given space. Poor speech intelligibility has been linked to poor concentration in multiple work environments regarding communication. Also, schools are largely effected by poor speech intelligibility, please refer to Builders Bulletin 93 (BB93).

  • Speech Transmission Index

Speech Transmission Index is a type of measurement used to measure Speech Intelligibility used in rooms where reverberation is an issue. It is rated between 0-1, where 0 is Bad1 isExcellent.



  • Cavity

A cavity is any given space between two surfaces, e.g a timber flooring with joists. An untreated cavity causes reverberation that would appear to resonate much like a loudspeaker.

  • Dot and Dab Plasterboard

Dot and Dab Plasterboard is a quick and cheap method of putting up a plasterboard using dabs of mortar and placing it onto the brick/block work. What this causes is an open air gap between the Dot and Dab and the brick/block work leading to poor acoustic performance, with walls to appear to resonate in the air gap. (We recommend removing Dot and Dab Plasterboard before installing any product.)

  • Floor Finish

Floor Finish is the top layer of the flooring, which may consist of; laminate, carpet, ceramic or any other finish that is available. Your floor finish will affect the acoustics in a room, where carpet is most desirable, laminate/tiled will reflect a large portion of sound and is less desirable.

  • Joist

Joist is the horizontal beams that support the structure, in regards to joists, we are looking at the ceiling and floor, and these can differ in spacing.

  • Stud Frame

Stud Frames are the vertical support in a structural frame and come in both Steel and Timber. These are sometimes untreated and act as an open cavity in a partition, it is recommended to treat the studded frames to increase acoustic performance.

  • Subfloor

Subfloor is what is placed onto the joists, the subfloor (if on a timber structure) needs to be a certain thickness to support the load in the room. In a concrete structure, a subfloor isn’t always required – it all depends on the condition of the floor.

Fig.1 – Flanking Transmission

Fig.2 – Impact Sound

Fig.3 – Early and Late Reflections

Fig.4 - Reverberation


[1] http://www.steelconstruction.info/images/thumb/8/8d/F_Fig2.PNG/400px-F_Fig2.PNG

[2] http://www.controlthenoise.com/16

[3] https://beatsandbots.wordpress.com/2013/03/21/reverb-reverb-reverb-part-1/

[4] http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/reverb.html