Noise control is the control of unwanted sound, typically, between distinct spaces. Where the sound source cannot be controlled directly, this is largely achieved by installing sound insulating systems, to form new or upgrade existing partitions. For more information on effective system design, please go to: ‘How effective are sound insulating systems?’

Acoustics (sometimes referred to as ‘interior’ or ‘room’ acoustics) is typically the control of sound within a distinct space, for example, moderating coloration, through the use of diffusers or reducing reverberation, through the use of absorbers. PSL – Case Study 1  shows an example of a sound absorbing system, applied to the ceiling of a school assembly hall. The system was designed and installed by Mute Soundproofing® to reduce reverberation times from 3.1 to 0.4 seconds, specifically to satisfy Building Regulations – Part E4 – Acoustic Conditions in Schools.

In certain circumstances, acoustics can be used as a method of noise control. Imagine, for example, a highly echoic room – when sound is omitted inside the room, the subsequent multiple reflections cause an increase in the overall sound pressure level, i.e. the sound source and reflected sound levels combine in intensity. This increase can cause a subsequent increase in outward sound passage, subject to the sound insulating performance of the separating structures. To mitigate this effect, the acoustics inside the room can be altered, i.e. to suitably reduce reverberation.

Flanking sound transmission, as defined by the National House Building Council (NHBC), is sound which travels in any direction, other than directly through the separating element. For example, under a door, via an open threshold or over a partition wall, via a suspended ceiling cavity (commonly observed in office buildings).   

The ‘A’ means A-weighted, an internationally agreed frequency response, generally similar to that of the human ear, so that A-weighted sound levels in dB correspond reasonably well with what is heard.

L = Sound Level

LA90 (dB) = The sound level exceeded for 90% of the measurement period.

LAeq (dB) = A measurement parameter designed to represent a varying sound source, over a given period of time, as a single number. This number is a measure of the energy contained within the sound at the point of the receiver.

LAFmax (dB) = The A-weighted, fast, maximum sound level. An LAF measurement will take approximately 0.6 seconds to reach 80 dB and just under 1 second to drop back down to 50 dB.

LASmax (dB) = The A-weighted, slow, maximum sound level. An LAS measurement will take approximately 5 seconds to reach 80 dB and just under 6 seconds to drop back down to 50 dB.

The ‘S’ function may be more appropriate when measuring a signal that oscillates very quickly, whereas the ‘F’ function may be more suitable when the signal is less impulsive.

Planning permission is generally required for alterations affecting the external fabric or footprint of a building. Effective sound insulation often involves upgrading exterior windows and doors; architectural features which typically fall within the remit of the local planning authority, particularly in conservation areas. Where restrictions do apply, alongside any planning applications, it’s worth exploring internal solutions, such as secondary glazing.

In terms of listed buildings, extra caution should be employed, as numerous external and internal features may be protected. These can only be altered on receipt of listed building consent. It’s a criminal offence not to seek consent when it’s required and not knowing a building is listed is not a defence to any criminal proceedings. Accordingly, any doubt should be investigated and discussed with the local planning authority.

A licence to alter (or freeholder’s consent) is the consent required by a leaseholder wishing to alter a leasehold property. It’s issued by the landlord or freeholder, therefore, it’s prudent to consult with them, before undertaking any notable works. For share-of-freehold properties, consent should be sought from the co-freeholders and/or presiding management company.

Party wall agreements are generally required where works involve structurally altering the party wall and/or integrating with party wall, ceiling or floor cavities. Cavities between dwelling-flats, for example, are often shared spaces or, in the case of leasehold properties, the property of the freeholder.

Robust domestic sound insulating systems, for ceilings and walls, involve independent structures, typically extending out, from the primary structure, between 170mm and 250mm, subject to levels and clearance depths.

Certainly, there are systems available which occupy less space, i.e. starting at 30mm, for both ceilings and walls. Moreover, there’s often the option to utilise existing cavities, which is clearly a space efficient way to work. That said, space efficiency should not take precedent over utility, i.e. there’s little point in implementing a system that physically fits, but is not fit-for-purpose. For more information on effective system design, please go to: ‘How effective are sound insulating systems?’

Building Regulations – Part E only apply to new builds and/or where there’s material change of use, i.e. there’s a change in the purposes for which or the circumstances in which a building is used. So, for example, after that change:

1. the building is used as a dwelling, where previously it was not;
2. the building contains a flat, where previously it did not;
3. the building is used as a hotel or a boarding house, where previously it was not;
4. the building is used as an institution, where previously it was not;
5. the building is used as a public building, where previously it was not;
6. the building, which contains at least one dwelling, contains a greater or lesser number of dwellings than it did previously;
7. the building contains a room for residential purposes, where previously it did not;
8. the building, which contains at least one room for residential purposes, contains a greater or lesser number of such rooms than it did previously or
9. the building is used as a shop, where previously it was not.

Note, this list is not exhaustive, therefore, it’s prudent to seek comprehensive advice from the local authority building control team, before undertaking any notable works.

For more information, please view the regulations page.

Building Regulations – Part E3 applies to common areas, such as stairways, corridors and entrance halls within buildings containing flats and apartments and including hotels, hostels, nursing homes and student accommodation.

Building Regulations – Part E4 applies to rooms and spaces within schools. 

Office buildings, for example, are not under the jurisdiction of Building Regulations – Part E and very often the sound insulation standards inside these buildings are not fit-for-purpose. There are the Control of Noise at Work Regulations 2005, however, these relate to safe working conditions, rather than construction standards.

For more information, please view the regulations page.

Office buildings are not under the jurisdiction of Building Regulations – Part E (or any similar sound related legislation). Accordingly, office fit-outs tend to prioritise build efficiency, typically employing lightweight partitions and doors, built atop raised floors and/or to the underside of suspended ceilings (with the cavity used to carry mechanical and electrical services, across the floor area). These types of separating structures do little in terms of noise control and often require upgrading, in order to provide office personnel with quiet/confidential work spaces. Mute Soundproofing® frequently undertakes such remedial works, however, wherever possible, sound insulating systems should be designed and installed as part of the original fit-out. For more information on effective system design, please go to: ‘How effective are sound insulating systems?’

Sound insulating systems are effective, if they’re specified correctly. Accordingly, wherever possible, the design process should taken into account the follwing 5 factors:

1. The sound pressure level(s) (SPL) of the sound source and, where applicable, the sound insulating performance of existing partitions, i.e. sound insulating systems are finite – they’re effective, until sound levels exceed their attenuating capacity. For example, if a system provides 50dB sound insulation and the sound source peaks at 80dB, then there’s a potential performance deficit of 30dB. Where there are existing partitions in place, their sound insulating performance should be factored-into the equation.
2. The sound frequencies of the sound source, i.e. different sound insulating systems are more or less efficient at attenuating different frequencies and, as a rule-of-thumb, lower frequencies, i.e. sub 400Hz, are harder to control than mid/high frequencies, requiring more invasive solutions, notably, in terms of mass-loading and structural isolation.
3. The pathway of the sound source, i.e. where existing partitions are in place, sound passage occurs, most prevalently, via the route of least acoustic resistance. This may not always be across the primary partition, rather, it may, for example, be through a connecting ceiling cavity, nearby window or door. This is what’s commonly referred to as ‘flanking transmission’. If overlooked, flanking transmission can significantly undermine the efficacy of any surrounding sound insulating systems.
4. The SPL differential, between the sound source and background noise, i.e. ambient sound can have a masking effect, such that, for example, when it decreases (typically at night, as general activity subsides), the potential audibility of the sound source increases; and vice versa (assuming the sound source remains relatively constant). Ideally, therefore, the design process should, where appropriate, account for any such fluctuations and specify accordingly.
5. The suitability of the space to accomodate the requisite sound insulating system, i.e. it’s not always practicable for the most effective system to be installed. For example, it may obstruct important architectural features, occupy too much space or exceed weight limits.

To fully satisfy the aforementioned lines of enquiry, sound testing and structural investigations are often required. Of course, not all projects warrant such in-depth analysis. In some cases, the circumstances simply won’t permit it, so the feasibility of the project needs to be assessed, based on the information available.  

Sound insulating products should come with supporting test data, issued from an accredited testing laboratory and including the following critical information, i.e. only with the benefit of this information, can the quoted sound insulating performance values be validated and/or compared:

1. The ‘configuration’ tested, i.e. the test data should specify whether a product was tested in isolation or as part of a supporting structure. Very often, performance values relate to a product, in combination with a wall, ceiling or floor construction. In this instance, the precise build-up of that construction should be described, as a product’s performance can vary greatly, depending on how it’s configured with other building elements.
2. The ‘range of sound frequencies’ tested, i.e. how a product performs at 40Hz, for example, is, typically, very different to how it performs at 4000Hz. Therefore, the test data should include performance values for a broad range of frequencies, i.e. a single, weighted value, as is often quoted, is only a partial representation of a product’s overall performance capacity.
3. The testing environment, i.e. the test data should specify whether a product was tested in the field or in a laboratory. Certainly, the latter is a more controlled environment. Accordingly, performance values, recorded under these conditions, tend to represent a best-case scenario, irrespective of extraneous effects, such as flanking transmission, which are commonly observed on-site.
4. The total surface area tested, i.e. meaningful performance values typically relate to a test area of > 10m².

To help answer this question, a ‘real-life’ case study shall be referenced, involving a standard construction, mid-twentieth century Victorian conversion, comprised of four flats (two on the ground floor, one on the middle floor and one on the upper floor).

Mute Soundproofing® delivered a schedule of impact and airborne sound insulation tests, between the middle and upper flats, notably, ‘before’ and ‘after’ a carpet (with underlay) was installed atop engineered timber floors. Table 1, below, details the results.

Table 1:

Additionally, Mute Soundproofing® specified and installed an independent ceiling system, directly beneath the existing separating ceiling, between the 2nd bedroom of the middle flat and the kitchen of the upper flat. These rooms too were subject to the same schedule of ‘before’ and ‘after’ impact and airborne sound insulation tests. Table 2, below, details the results.

Table 2:

So, based on the field data above, in terms of insulating impact sound passage via a separating floor/ceiling, a carpet (with underlay) comfortably out-performs a robust acoustic ceiling system. Whilst, in terms of insulating airborne sound passage, the opposite is true. However, it would be fair to say that, based on the performance differentials between the two options, a robust acoustic ceiling system provides a more balanced solution, overall.

Note, in order to verify compliance with Building Regulations – Part E, impact sound tests cannot be conducted on a floor with a soft covering. Therefore, carpeting is not recognised by Building Control as a means by which to achieve Part E compliance.

For more information, please view the regulations page.

Doors, generally, are not airtight, consequently, in terms of insulating airborne sound passage, they under-perform.

The table below details the results of an airborne sound insulation test, conducted by Mute Soundproofing®, involving a fully-fitted, solid-core, non-glazed, 30 minute fire door, ‘before’ and ‘after’ it was made airtight. The data includes the positions where resistance to sound passage was ‘highest’ and ‘lowest’, i.e. at the door’s centre and threshold, respectively. 

To put these results into context, as per Professor Colin Hansen’s ‘Fundamentals of Acoustics’, a sound level reduction of 10dB, is generally perceived, by the human ear, as a halving of loudness.

So, based on the field data above, the airborne sound insulating performance of an existing solid-core, non-glazed door can be significantly improved through airtightness alone. In large part, this is achieved by installing suitably specified acoustic perimeter and threshold seals. However, features such as key holes, letter plates and spy holes also need to be taken into account, as these too can compromise airtightness.

In terms of hollow-core doors, their airborne sound insulating performance can also be improved through airtightness. However, typically, they lack the intrinsic mass to perform adequately, overall. The same is also true of glazed doors, notably, in relation to the glazed elements, which need to be assessed in isolation.

Where existing doors lack the requisite mass, high-density acoustic cladding can, sometimes, be added. However, this application increases the thickness of the door, therefore, other related adjustments may be necessary.

Many sound insulating materials include a thermal rating and, as such, can be used to provide a combined solution. Moreover, airtightness, i.e. the control of inward leakage of outdoor air, is a critical condition for sound and thermal insulating systems.

Wherever possible, Mute Soundproofing® specifies products which are either, fully or partially recycled and sustainably sourced. Product specific data is available on request.

In terms of workmanship, Mute Soundproofing® provides a 2 year guarantee, with a defects liability period written into all contracts.

In terms of acoustic performance, Mute Soundproofing® is a proponent of pre-works and pre-completion sound testing, as a fail-safe way of verifying compliance with pre-specified acoustic performance criteria.