Soundproofing Basics

Basic Soundproofing Help and Advice

INTRODUCTION

Sound Insulation is the name that is given to describe the reduction of sound which passes through a structure. When sound is carried between two spaces the sound energy takes two routes.

The first is directly through the wall/floor.

The second is indirectly through the surrounding structure and this is called ‘flanking’ noise.

This type of noise often takes deceptive routes around a structure such as the walls and floor which flank a partition or an open window, air ducting, doorway or corridors etc.

This is why it is extremely important, when building an acoustic partition, to make sure that everything is airtight as the smallest crack or hole can let huge amounts of sound through.

If you have a noise problem the first thing to address is the weakest part of the structure in question.

The sound insulation of walls is normally only related to airborne sound such as speech or the TV but floors usually need to protect against the transmission of impact sound such as heavy footsteps etc.

Generally the average airborne sound insulation of a solid structure is governed by its mass. The heavier the material the more effective it is at resisting airborne sound transmission.

The soundproofing performance of any additional structure will always be better if the additional higher mass layers are isolated from the existing structure.

Remedial actions for improving wall acoustic performance

If you are having noise problems with an existing partition wall the first thing to do is inspect the wall and adjoining areas of abutting walls closely to ensure that optimum sound insulation is being achieved.

Any small holes or cracks will let significant amounts of sound through so they will need to be sealed with mastic if small or mortar if large. DO NOT USE EXPANDING FOAM FILLERS for this purpose.

The area of the wall in the roof space should also be examined. Any missing bricks should be replaced. Any small holes, cracks or unfilled mortar joints should be sealed with sand and cement mortar mix.

There may also be holes, cracks or bad mortar joints in concealed areas such as behind skirting boards, in the space between the floor boards and ceiling or underneath a wooden ground floor. You will need to lift the floorboards to check these areas.

If the joists run into the wall then check for gaps between the joists and wall. If any are found they too should be sealed with the appropriate material. Any cracks at the junction of the wall with the ceiling or floor should be sealed.

To give you an idea of the difference this alone can make: Any hole or gap will reduce the performance of a partition SIGNIFICANTLY. A 25mm square hole, in an otherwise acoustically sound partition, can reduce the performance by up to 15dB!

A sound leak, amounting to one-tenth of one percent of a partition area, will limit the effective performance to around 30dB even if the partition was rated to be around 55dB.

For example, in a wall of area 10m² a gap this size would have an area of 10cm² and would be obvious as a hole. HOWEVER a crack 1mm wide by 1m long at a periphery point would be just as detrimental.

Cracks such as these can often go unnoticed especially where a mastic seal has been omitted or incorrectly applied.

Acoustically Uprating Domestic Masonry Walls

How your walls approximately rate:
Normal speech can be heard easily – 25dB
Normal speech audible but unintelligible – 30dB
Loud speech can be understood – 35dB
Loud speech can be heard but unintelligible – 40dB
Loud speech can be heard faintly – 45dB
Shouting can barely be heard – 50dB
Shouting cannot be heard – 55dB

To increase your wall’s performance we offer two primary solutions:

The first is to use our CAD20-WP panels and two additional sheets of 12.5mm (or thicker) plasterboard. The CAD20 panels ‘isolate’  the additional plasterboard from physical contact with the existing wall and damp the vibrations before they are transferred to the outer plasterboard. The whole assembly glues together and only takes up 50mm of space from the wall. An average 100mm (4″) brick wall gives around 39dB and even a 100mm cavity brick wall only gives around 47dB of performance. CAD20 with only 25mm of additional plasterboard has a figure of 48dB DnT,W+Ctr. M20 is also much more efficient than standard mineral wool backed plasterboard liner board.

The second, much better option, is to build an isolated studwall in front of, and not touching, the existing wall. This ideally involves incorporating Acoustic Mineral Wool  or even better 2FTex quilt in the cavity space, resilient bars to hang additional plasterboard to the studs and soundproofing mat sandwiched between the two sheets of plasterboard. The more isolation and damping that is applied to the studwork and materials the better the performance will be. 
VL65 acoustic membrane can also be applied across the entire bare framework first for even better performance. The deeper the cavity space the better the performance especially at the lower bass frequencies.

Acoustically Uprating Domestic Plasterboard Partition Walls

To increase the performance of a stud partition, that already has a plasterboard face, you can use our  CAD20 panels  with 25mm of additional plasterboard on top.

If you are happy to remove the plasterboard that is already there you can fill the cavity space with Acoustic Mineral Wool or even better 2FTex quilt before adding resilient bars then two layers of plasterboard with soundproofing mat sandwiched in the middle of the plasterboard sheets. Again VL65 acoustic membrane can also be applied across the entire bare framework first for even better performance.

Care must be taken to avoid direct contact between the additional plasterboard sheets and the existing structure (floor/ceiling/side walls).

If you are building a new stud partition it is essential to do everything you can to damp and isolate the structure. You should add two strips of soundproofing mat around the periphery of the frame to help isolate the frame from the surrounding structure. You should mastic seal the frame airtight (around the edges) before adding the additional materials. Plasterboard should ideally be screwed to the studs rather than nailed.

If you are really limited to room space the most basic thing you can do is to add a strip of acoustic membrane to the front faces of the studwork which will help isolate the plasterboard from the face of the studs. You should then add two layers of 12.5mm plasterboard with a layer of soundproofing mat sandwiched in between. This will bring the wall face out only 30mm. You should still make sure that the additional plasterboard does NOT touch the surrounding structure, this small gap should be sealed with flexible mastic sealant.

Uprating Domestic Timber Floors

A standard tongued & grooved (T&G) chipboard floor will stop around 37dB of airborne noise reduction and let through around 80dB of impact noise. If you have ‘gapped’ square edged floorboards then you have very little soundproofing performance because the only layer of sealed mass will be the plasterboard ceiling below. The noise will NOT be blocked, in any way, by floorboards with gaps between them so the performance will be even worse than that described above.

The most basic thing to do is to lift the floorboards and add 100mm Acoustic Mineral Wool  in the cavity space. You should then seal up the gaps and cracks between the existing square edges floorboards and then add a sealed hardboard top layer. You ideally also need to add an additional sheet of 12.5mm plasterboard to the ceiling below. This will improve the airborne noise reduction from less than 37dB to around 43dB.

In most situations it is impractical to install additional plasterboard to the ceiling below so instead you should add one (preferably two) layers of  Tecsound 50 acoustic membrane to the floor above. This will significantly increase the floor’s mass as well as damping out the vibrations which will still try to get through. This will increase the airborne noise reduction up to about 45dB.

If impact AND airborne noise are the problems then you need something more resilient under the top floor layer.

The simplest option would be to install a really good quality carpet underlay beneath the carpet. This will improve impact noise by up to 15dB but will only marginally (if at all) increase the airborne noise performance. Alternatively you can lay Quietfloor Premium+ directly beneath carpet to improve both the airborne AND impact noise even further.

If you are laying a wooden top floor (with no carpet) you should consider using either Isobase R50 floor isolation OR lay our Quietfloor Premium+ beneath the proposed top floor.

Both the previous options ideally require acoustic mineral wool in the joist space and for the floor to be sealed airtight before proceeding.

It must be remembered that increasing the mass of a floor will inevitably increase its height in the room and that doors may need to be trimmed so that they still close. This can also make a stepped lip between rooms which may not be convenient.

To improve the floor performance with reduced height rise you should lift the floorboards and install plasterboard plank inserts between joists to bring the surface level flush with the top of the joists. This will give you a sealed base floor the same height as the top of the joists. From there you can add whatever products are necessary and save yourself about 10mm of height rise.

The thicker and denser the inserts, the better.

Your noise problem, space limitations and budget will determine what product(s) will be your best solution. If you are unsure please call us so we can help find the most appropriate option for your situation.

Some examples are as follows:

• You can add acoustic membrane if airborne noise is the only problem.
• You can add a decent carpet underlay if impact noise is the problem and you are having a carpet finish.
• You can add acoustic membrane and decent carpet underlay if airborne and impact noise are both contributing to the problem.
• For improved performance you can add Quietfloor slabs if the problem is both airborne and impact noise. These can be installed directly beneath carpet or wooden top flooring.
• You can add isobase floor isolation if impact noise is the problem and you are installing a wooden top floor.