dBx Jargon Buster

Welcome to the dBx Acoustics jargon buster! In this section, we list some common acoustic terms as well as standards and guidance you may be asked to comply with. If there’s something you need to know that we haven’t covered here, please let us know.

Sound Insulation

Sound insulation is the term used when talking about how much sound passes from one space to another. There are two types. Airborne sound insulation relates to noise such as speech and music, and is relevant when designing both walls and floors. Impact sound insulation is considered in the design of floors and ceilings, and relates to the control of noise from (typically) people walking on the floor above being heard in the space below.

This is sometimes referred to as ‘soundproofing’, but it is important to understand that nothing is ever truly soundproof! The key is to control noise transfer to within an acceptable level, based on the typical activities which will occur in the spaces under consideration.

Reverberation Time

Reverberation time (RT) is a measure of how quickly sound decays, but in layman’s’ terms it can be considered as how subjectively ‘echoey’ a space is. For example, a church or cathedral typically has a long reverberation time, while a recording studio would typically have a very short reverberation time.

A shorter RT is desirable for speech, for example in offices or classrooms, while a longer RT can support music. Often where a space is considered ‘too noisy’, for example a busy bar or restaurant, control of reverberation can help.

Reverberation is dependent on the quantities of acoustically reflective and acoustically absorptive (‘soft’) finishes within a room – for example, a room with carpet will sound very different when you take that carpet up. In acoustic design, the quantity, specification and placement of acoustically absorptive surfaces, as well as surfaces which diffuse (scatter) sound, can be used to optimise conditions for the proposed use.


ProPG: Planning & Noise (Professional Practice Guidance on Planning & Noise) – New Residential Development is intended for use for new residential developments on land exposed to transportation noise. The guidance proposes a two-stage approach; an initial site risk assessment to be carried out before any planning application is made, and a full assessment where four key elements are considered in detail to produce an Acoustic Design Statement.

The Acoustic Design Statement must demonstrate consideration of good acoustic design (including providing adequate ventilation and avoiding overheating), compliance with noise levels in dwellings and external amenity areas, and the consideration of any other relevant issues.


The National Planning Policy Framework (NPPF) and Noise Policy Statement for England (NPSE) together set out guidance on the suitability of planning conditions, and the planning intent for noise including environmental noise, neighbour noise, and neighbourhood noise.

The policy aims to avoid significant impacts on health and quality of life, and where possible contribute to the improvement of health and quality of life. The NPSE provides some context, describing ‘effect levels’ at which noise may lead to changes in behaviour. This ‘noise exposure hierarchy’ can be used to assess the potential impact of noise and whether further steps to control it are required.

HTM 08-01

Health Technical Memorandum 08-01: Acoustics sets out acoustic criteria for new healthcare developments. It includes acoustic criteria for speech privacy between rooms, noise levels in rooms both from building services and from external sources, and impact sound from rooms above. Specific guidance is given for audiology facilities.

The guidance also covers refurbishments and temporary healthcare premises, and the control of noise and vibration during construction.


The decibel, written dB, is the unit by which sound levels are expressed. A level of 0dB is near total silence; a normal conversation may be around 60dB, a rock concert may be above 100dB.

Decibels often cause confusion as they add logarithmically -two noise sources of 40dB added together results in 43dB, not 80dB! As a rough guide, the smallest change in noise levels that humans can detect is typically around 3dB. Something which seems subjectively ‘twice as loud’ is likely to be around 10dB higher.

Acoustics – where 2+2 really does equal 5…!

Control of Noise at Work Regulations

The Noise at Work Regulations set ‘action values’ dependent on the level of noise to which employees are exposed. This can be considered both in terms of daily and weekly exposure, to take into account different working patterns. Where the lower action level is met, hearing protection must be made available to employees. At the upper action level, employers must ensure that hearing protection is used.

The regulations also put a duty on employers to take all reasonable steps to reduce noise at source.

Code of Practice on Environmental Noise Control at Concerts

The Code considers noise from large-scale music events at outdoor venues, and is primarily used for venues where music occurs for no more than 12 days per year – for example festival sites, or sports arenas used for occasional music events.

Criteria are presented for acceptable noise levels at noise sensitive properties, dependent on the type of venue and the number of events held per year. The guidance also recommends that when events continue beyond 23:00h, music should be inaudible within residential premises.

Guidance is given on appropriate licencing conditions, and noise control methods.