Technical Information
Soundproofing
We know a lot of people use this term, but we don’t really like it, let us explain
why. The dictionary definition of the adjective soundproof is ‘not penetrable by
audible sound’. With high sound levels it takes a very dense structure to totally
eliminate audible sound, acoustically this is usually impractical, if not impossible,
to achieve. So, when it comes to unwanted sound (noise to you and me), we prefer to
consider its attenuation or reduction.
A lot of enquiries we receive relate to common acoustic problems, such as the sound
of traffic transmitted through windows and noise from neighbours penetrating party
walls, floors, ceilings or doors. We will take a look at each of these here and offer
some practical advice and solutions.
Traffic Noise
If you live near a busy road you are probably well aware of the nuisance this can
present. The transmission of traffic noise into buildings is usually through windows
or doors. In most cases it is unlikely that high levels of sound will penetrate the
building structure, as the high mass provided by walls will usually adequately
attenuate much of the sound energy.
What can we do about sound entering through windows?
We get asked a lot whether our acoustic curtains can help, the answer unfortunately
is no, as they do not provide additional mass. You’ve probably guessed by now that
increasing the density or mass of the weak parts of the structure is the key to
controlling noise intrusion. So with windows secondary glazing, which unfortunately
we do not supply, or blocking up openings is the only solution. The airspace between
any additional and existing glazing needs to be as wide as is practical and the new
pane should be of dissimilar thickness and as heavy as possible, say 6.4mm or 8.8mm
laminated glass. This must be seated in a frame that is acoustically sealed and with
opening elements to meet the building regulations. It is also useful to acoustically
line the reveal between the panes to absorb sound within the cavity.
If the sound is only a nuisance say at night or perhaps you play a musical instrument
and you want to contain the sound, a panel to cover the window could be the answer. Clubs
and bars sometimes use this approach when they have music or live acts late in the evening.
This can be a relatively inexpensive way of adding mass over a weak area but you do need
somewhere to store the panel when not in use. Figure 1 shows how this can be done. Prices
for supply and installation are available on request.
How do I improve doors?
Well the easy answer is to replace poorly performing doors with purpose made acoustic
doors (Acoustic Doors.pdf). This can, however, be expensive and is not always necessary.
There is probably not much that can be done to improve a hollow core door or one that has
huge gaps at the threshold and around the jambs, but if the door is of solid construction
and well fitted, the addition of acoustic seals (Acoustic Door Seals.pdf) may be all that
is needed. Prices for supply and installation are available on request.
Another option is to use a panel to fit within the doorway, as per the above window
treatment. This can be manufactured in a similar fashion to that shown in Figure 1, but
adapted to keep the floor area clear of any permanent fixtures.
Noisy Neighbours
A common problem with flats or offices shared by several occupants, or any building with
party walls, is the passage of sound from one space to another. This can take the form of
either airborne or structure borne sound transmission. The first step is to try and identify
which is the problem and what route the sound is taking – not always an easy task!
How do I stop sound travelling through a wall?
With airborne sound transmission the best way of adding additional mass to reduce sound
intrusion or escape is to construct a secondary wall over the face of the existing substrate.
This should comprise isolated battens attached to the wall, with mineral fibre between, over
which should be fixed two staggered layers of Soundbloc plasterboard, separated by a decoupling
barrier mat (Secondary Wall Structures.pdf). Once constructed this can be plaster skimmed and
decorated in a conventional fashion.
How can I stop the sound coming through the ceiling?
If this is structure borne sound, such as the impact of footsteps on the floor above, it is
usually better to treat the floor. This can be readily tackled with composite construction
boards, laid over the existing floor surface, to provide a means of decoupling the impact and
adding a little additional mass (Overlay Acoustic Flooring.pdf).
In multiple occupancy dwellings there is usually little chance of getting the resident above
you to treat his/her floor, so the only respite from the noise nuisance may be to add mass to
the existing ceiling structure. This can be done in various ways. In its simplest form this
could comprise the direct fixing of further layers of plasterboard to the existing ceiling
substrate. Whilst this may seem a practical and easy way of adding mass the acoustic benefits
will be much greater if the additional treatment is suspended from the existing structure to
form an airspace. This is known in the trade as an MF (metal frame) ceiling. This comprises
lightweight metal sections, suspended from the existing substrate, to form a framework that
Soundbloc plasterboard can be attached to. The plasterboard should comprise two or three layers
with staggered joints, isolated from the existing wall around the periphery with a neoprene seal.
The top side should support a layer of sound absorbent mineral fibre. The structure can be
mounted relatively close to the existing ceiling where height clearance is a concern although
greater depth airspaces will provide better performance. The new ceiling can be plaster skimmed
and decorated following completion.
What can I do to stop sound travelling through my floor?
If the floor is solid concrete then there is, in all honesty, probably little you can do. It will
be difficult to add sufficient mass to provide an acoustic benefit where there is already a high
mass structure. If, however, the floor is a timber construction, composite construction boards
can be laid over the existing floor surface, to provide a means of decoupling impact sound
transmission such as footfall and adding a little additional mass to mitigate airborne sound
transmission (Overlay Acoustic Flooring.pdf).
It should be noted that with respect to all of the above room treatments it is assumed that sound
is transmitted directly through the substrate that is to be treated. In many cases flanking
transmission may be experienced. This is where the sound is bypassing high mass elements within
the building structure and travelling via the weakest elements. This could include windows, doors,
stairwells, service ducts or common elements between dwellings.
If you require any further information or would like to arrange for an engineer to visit, please
do not hesitate to contact us.
