Why Soundproofing dB figures are only a guide? 

The dB performance figures provided on our website and within our literature are based on laboratory and on-site tests. However, these are not guaranteed, as site conditions, building construction and installation standards may affect the final performance of any soundproofing.

There are four parts of the equation which can influence the perceived performance of dB figures:

1. How we as humans all perceive levels of sound differently ?
2. How well does the existing structure perform?
3. Quality of installation
4. Flanking noise
5. Room acoustics and reverbaration

Sound is ultimately expressed in decibels (dB) however, as humans, we vary considerably in our awareness to noise levels. 

For example:

• In a bedroom at night when it is dark and quiet, we are normally more susceptible to noise. (e.g. you can hear a pin drop at night but would not notice it during the day)

• Once you have heard a noise you tend to listen out for it, which makes the noise appear to be louder than it is

• Different people are susceptible to different sound frequencies (some higher sound frequencies can only be heard by children but not by older adults)

• “The noise that is annoying my partner does not bother me” is a common statement we often hear

• Some people are highly sensitive to noise, and any noise - even leaves rustling may be considered annoying

• External noises such as traffic can be considered as excessive noise, however human beings are very good at adjusting to this and after time, we may no longer notice this noise

• A small clicking noise in your car may be driving you mad because you know how your car should sound, however anyone new entering your car may not notice the noise at all

• Noise on your side may appear louder if you have changed flooring from carpet to a solid floor. Not having anything to absorb sound on your side means any noise will be amplified due to an increase in echo and sound reverberation

• An average quiet room is normally around 35dB which shows we are all used to noise around us, however anything above this might be considered annoying or loud

• How do you measure the noise? Do you put your ear to the wall (which would amplify the noise like putting an upside-down glass to the wall) or do you stand 2 meters away and gauge the noise level?

• If you have emptied your room for renovation and you just have hard surfaces everywhere, then sound will echo and resonate, amplifying the noise from next door. However, once you have put back carpets curtains and soft furnishings there is normally enough soft material to stop sound echoing and reverberating reducing your perceived levels of noise form neighbours

Construction and density of standard structures can vary considerably.

A good example would be a solid partition wall between neighbours which is commonly constructed of brick. A standard brick wall will normally block around 40dB, however different performances will be achieved due to factors such as:

• There being over 150 different types of bricks which can vary greatly in density

• Different bricks degrade over time and at different rates

• The mortar between the brick may vary in quality, be of poor quality, or have degraded over time

• The original wall may have been damaged at some point in its history (i.e. had kitchen fitting piercings through the bricks and mortar) which are hidden by a skim plaster or plasterboard

• There may have been a fireplace at some point which has been covered over, hiding a thinner wall and a cavity

• Some older properties which have been divided in two may have had a door between them at some point in the past, which may now be simply covered over with thin boards

• If the existing wall performs very well for soundproofing to start with, adding soundproofing to this type of wall will not give you the same percentage increase as adding soundproofing to a lower performing wall

Differing performances can also occur on timber joisted ceilings / floors:

• Performance can vary due to the type of wood used on the base floor, as different density woods perform differently

• Old floorboards may have gaps between the boards or may have been patched with different types of wood

• The depth of timber joists also means results may vary considerably

• The type of wood used for the timber joists can impact results, for example wood and metal I-joists perform worse for impact noise

• The span of the floor, as (certain) larger rooms are more prone to flexing and vibration

• The spacing of the timber joists

• The type of insulation, if any has been used between joists

• The type of ceiling boards varies considerably in density i.e. Lath and Plaster is denser that standard plasterboard

• Small gaps around the perimeter where the floor / ceiling meet the walls may provide a path for sound to travel

• Different final floor types (e.g. carpet v wood) affect the results, as hard floors can reduce the impact performance by 3dB

The quality of installation is almost as important as the soundproofing material being installed, as any small gaps will negate the benefits of the soundproofing system. 

An excellent example of this is if you wind down the window in your car a very small amount, you can hear everything outside perfectly clearly, then close the window and your car will be nicely soundproofed. 

This illustrates how much sound can pass through even the smallest gaps.

• All small gaps must be sealed with acoustic sealant and larger gaps filled with standard building materials.

• Plug sockets must be addressed with acoustic putty pads, as these can also be weak points.

Flanking noise is when noise travels around the structure and through weak points. This can also potentially influence dB results.

Typical wall examples below:

• If the floor / ceilings are timber joisted and the timber joists go into the partition wall there may be some poor construction (gaps around the joists in the wall). If there are gaps, any noise that gets into the void between the joists can echo and resonate and amplify in this sealed chamber. Think about shouting down a cardboard tube and how this amplifies noise. 

• The wall may be constructed of very dense concrete and have joining internal walls. When sound hits a wall, it becomes an energy and a vibration which travels through the wall. It also travels up, down and sideways and the denser a material is the further the vibration will travel. Think about the western films where they listen for the oncoming train by putting an ear to the track, or inmates communicating by hitting metal pipes!

• Stud walls can also be subject to flanking noise to joining stud walls if the cavity between the plasterboards and the joining stud walls are open to each other, as this offers an empty space for sound to travel through to the joining wall.

Different sizes of rooms and different hard surfaces within a room can affect the volume of sound within a room.

I.E rooms with hard floors and walls will not have the same ability to absorb sound as rooms with soft carpets, curtains and soft furnishings, and in certain circumstances can actually amplify noises in different areas of the room (I.E corners are base traps)