Blog

Soundwaves will find their way through the weakest points or links within a structure easily if present.

And if one were to carefully consider a structure, there are numerous weak points that need to be addressed if sound transmission is to be handled effectively.

Flanking noise is just one example of unwanted sound that can enter a building or a room if the structures allow it.

We explore what flanking noises are and how to tackle them in the chapters below.

What is Flanking Noise?

Flanking noise is a term used to describe the noise that reaches a room through an indirect path.

For example, noise can pass through ductwork, slabs, ceilings or floors.

Sound can manage to pass around, under or over the top of a partition that separates two spaces.

Flanking noise, as you can imagine, can be quite a problem as it can essentially reduce the effectiveness of a wall, floor or ceiling installation.

And, it can become bothersome in multi-family residential buildings if the structures produce large amounts of flanking noise.

Sources of Flanking Noise

Flanking can result from both airborne as well as impact sounds.

Any building element, structure or material which penetrates a separating element, structure or material can lead to flanking transmissions via the route created by the continuation.

Structural Steel & I-Beams

Quite a common cause to increased flanking transmissions can be structural components within a building such as steels, beams and lintels.

Due to their positioning spanning over a considerable length and structural integrity, they can offer a perfect pathway or motorway for sound transmission.

Their material and natural resonant frequency can be seriously problematic with certain frequencies as the vibrations can in effect be amplified or resonated the full length of the steel.

Shared Structural Components

Floor joists and boards, continuous drywall partitions and concrete floors are often shared structural components in buildings.

As a result sound can find a direct pathway through which to pass.

Ceilings

Ceilings act as common flanking sound transmission pathways, as sound can pass both above as well as through the ceiling.

Even though the ceiling can be soundproofed with a suitable acoustic isolation membrane, there may well still be residual sound that carries up or down the load bearing walls.

Floors

Sound can pass through the floor and floor joist space.

The weakest point is where the walls meet the floor and this is where most flanking noise manages to pass, especially in multi-storey buildings.

Windows

Windows are weak points in any building when it comes to sound transmission.

If you look at a window and consider it in relation to sound, you soon realise that it is a large empty gap in the wall which ends up allowing noise to penetrate, as well as amplifying sound transmission.

Doors

Consider having a door connecting two rooms, and you need to stop sound from going from one room to the other.

The door is a weak link, as a considerable amount of sound can potentially pass through it.

Even in cases when a door does not directly connect two rooms, sound can still pass through a door, down a hall, and into a neighbouring room for example, bypassing any efforts of a high quality soundproof wall.

Electrical Sockets

Electrical outlets can be a problem when it comes to sound isolation.

Even if small, electrical socket outlets create holes in walls.

Often electrical outlets are poorly sealed as well, which means sound can pass through easily.

Air Ducts & Plumbing

Ducts can be very problematic because they can provide a direct air path through which sound can travel easily from one area to another.

They can be a common cause of flanking noise in buildings with HVAC ducting installed.

Structure-borne Noise

Noise travels as mechanical vibrations through the structure of a building.

This includes walls, subfloors, joists and studs.

It will pass on to remote locations where the vibrations will stimulate the wall, floor and ceiling, and create noise.

Seals

Sealing is of great importance to reduce the amount of noise that manages to pass.

Even the smallest cracks left unsealed will make a difference.

It’s important to choose high quality acoustical sealants such as caulking and noise proofing compounds that can be as effective as possible for flanking noise.

Ways to Prevent Flanking Noise

Ideally, flanking transmission is given due consideration during the design and construction phases of a building.

This will improve the chances that it is reduced as much as possible before it even becomes a problem.

The quality of the workmanship is of great importance too to ensure that good noise control processes are employed and adhered to.

It is also best to ask the architect or builder regarding which steps were taken to ensure sound privacy from neighbouring houses or adjoining rooms as well as to deal with noise ingress from the outside.

Better still, having a professional acoustical consultant involved during the planning and construction stages will help prevent any potential flanking issues from evolving.

Nowadays there are also building codes that have minimum standards for noise control between residential units.

Upon completing construction works, there should be inspections to ensure that the building meets the minimum building regulations for sound isolation.

The following are some ways that can help to prevent flanking noise:

Acoustic Isolation Membranes

Adding acoustic isolation membranes into walls, floors and ceilings will help enormously to mitigate sound passage as well as also minimise vibration through the structure, thus reducing flanking transmissions.

Decoupling

Decoupling methods are a great way of reducing flanking noise considerably.

Where space and tolerances permit, creating a principle of a cell within a cell, or room within a room, by means of decoupled structure can divorce one from the other.

As an example, having two rows of studs used in combination with separate ceiling joists in order to create what is commonly referred to as ‘a room within a room’.

This is because in this case there will be practically no, or at least very little, mechanical connection between the room and the rest of the structure.

Other construction methods such as staggered studs can keep the sound vibrations away from the structure, thereby reducing flanking noise.

Open Cell Cavity Insulation

Installing an open cell cavity insulation (part fill or full fill) as appropriate into cavities is essential to assist with acoustic absorption.

This principle will also greatly reduce resonance, regeneration and amplification of acoustic energy, thus reducing the likely increase in energy and flanking transmissions.

Used extensively in the residential industrial and commercial fields QuietFibre is introduced where reverberant sound and increased resonance is a problem.

Resilient Channels

Resilient decoupling such as resilient channels or cross battening on studs, is a commonly used decoupling method.

Specialist acoustic hangers or acoustic clip systems with rails are also popular.

Using resilient channels can significantly help to reduce the amount of vibrations that pass through the structure, thereby improving the soundproofing of a building.

Adding Mass and Density

Adding mass can help initially by adding bulk and weight to deflect sound.

However be aware that the rigidity of the mass material itself being physically attached to the substrate can also provide a pathway for vibration and flanking transmissions, usually by more problematic frequencies.

The use of resilient channels and acoustic hangers in walls and ceilings for example, can assist with reducing direct linkage as previously mentioned, although this of course is at a cost of the additional depth to the overall buildup.

Floating Floors

Floating floors can help considerably in minimising structural connections.

As a result, flanking noise will be reduced.

A floating floor is one which has a material and surface installed without mechanical linkage and therefore floating over a resilient layer.

The resilient layer can be in various forms, most commonly acoustic isolation membrane.

Ideally a mechanical break is left between the floating element and the structure.

Acoustic Floor Cradles

Used in floating floor systems where increased tolerances and thicker finishes are available.

Made from 100% recycled rubber crumb materials, these AcoustiCradles offer a cost- effective acoustic flooring solution by de-coupling the floating floor from the structural floor.

Suspended timber battens are installed into the AcoustiCradles to reduce direct linkage.

Upgraded Doors

Doors can be upgraded by adding mass in the form of a sheet of MDF or plywood in addition to an advanced acoustic isolation membrane.

This will act as a decoupler, thereby greatly reducing the sound that passes through to other areas.

Using heavy, solid-core doors is a good way to add mass.

It is very important that one avoids installing hollow core doors.

Ideally, the door frame and perimeter jamb will be increased in depth to increase closure contact – more door to jamb.

Adding additional gaskets and weatherstrips to the door jamb can create a better quality seal.

Specialist Acoustic Doors

Nowadays you will be able to find various manufacturers that offer specialised acoustic doors.

These will have enhanced seals and be effective even for lower frequency noise.

Duct & Plumbing Liner

Insulated ductwork contains sound absorbing material, which helps to deal with sound as it travels through the duct.

This plumbing liner, or insulation will be within the duct, making it very effective in reducing flanking noise.

Having long and complex paths is also a good way of making the noise diminish, since with more bends and length, the sound will lose its energy while interacting with the duct liner even more.

Duct & Plumbing Soffits

Where feasible it may also be beneficial to wrap or insulate any ductwork with an acoustic isolation membrane to contain noise breakout.

An effective way to do this is by framing out the soffit and then wrapping with the aforementioned acoustic isolation membrane and open cell cavity insulation followed by a single or double layer of finishing board of choice – plasterboard or drywall.

Soffits can be made from acoustic isolation membrane, open cell cavity insulation, drywall, MDF or other commonly used building materials.

If the ductwork has to be exposed to sound, then a cylindrical duct is better than a rectangular or square duct.

Moreover, it would help if the duct is coated with a viscoelastic material in way of a lagging principle.

Acoustic Putty

Acoustic Putty Pads are flexible acoustic and intumescent firestop pads designed to maintain a building separation and a wall partition’s structural integrity and acoustic properties.

Acoustic Sealants & Caulks

The quality of your seals is also greatly important.

It’s crucial to bear in mind that even the smallest seal failure can translate into the weakest point allowing direct passage of sounds and flanking transmissions.

Even the most expensive partition will end up performing ineffectively if there is poor seal quality.

Remember, one is only as strong and effective as its weakest point.

It is best to apply multiple beads or layers of acoustic sealant on partitions to be super critical at these obvious potential weak points.

By doing so, a quality seal can be achieved, as you would effectively be doubling up on seals.

Hence, should one layer be compromised it would be backed up by the other.

Acoustic Hoods

AcoustiHoody fire & acoustic hoods are flexible fire and acoustic shields designed to retain fire line protection and conformity for fire and acoustic integrity of ceilings.

They can significantly reduce acoustic transmission through penetration.

Conclusion

By taking a look at key aspects relating to flanking noise, you can be in a better position to deal with it and reduce its negative impacts.

The success of any sound isolation project relies on various aspects, and while there are diverse methods and options to use, care needs to be taken to choose the most ideal soundproofing materials and applications depending on the situation, structure and type of noise.