Environmental Health: Sound

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Sound is a neutral term that encompasses both noise, which we find a disturbance and an intrusion, and pleasurable sounds, which we generally welcome. It is noise, and how to control it, that we are most concerned with in this section. How we experience noise is mostly subjective: it often depends whether we are making the noise or on the receiving end of it.

HOW OUR BODIES REACT TO SOUND

Sound impinges on our bodies as a series of pressure waves or vibrations that vary in intensity and frequency. The intensity (or pressure) of the waves determines the loudness of the sound, and the frequency determines the pitch (how high or low it sounds). When these pressure vibrations reach our body, they set up vibrations in all the cells immediately adjacent; if the sound is loud enough, the vibrations will travel to all parts of our body. There is evidence that each cell in the body is affected by the vibrations of sound. The ear is of course the organ that makes sense of these waves; it is able to pick up an incredible range of frequencies and loudness. These are transformed into nerve signals for the brain to decode and interpret.

The range of response of the ear is truly amazing. It is possible for the human ear to pick up sounds that are one-billionth the strength of the loudest sounds that can be heard without causing physical damage. Because of this vast range, a logarithmic scale is used to measure sound. This decibel scale starts with 0 decibels for the threshold of hearing, assigns 60 decibels for normal conversation and 120 decibels for the threshold of pain. The chart on the below gives some typical noises with their approximate decibel rating. Levels of sound fall into four categories:

• Background (ambient) sound

• Normal (healthy) sound levels

• Danger levels (for continuous exposure)

• Painful or damaging levels

Like other forms of sensory awareness, there is a level of sound stimulation that is both healthy and necessary for well-being. Below this, we suffer from sensory deprivation. However, with sound there is almost always back ground noise no matter where you are. It is only in deep space or in specially constructed studios that it is possible to experience no environmental sound at all (and it is impossible to eliminate the sounds produced from within our own bodies).

Above this basic background level comes the normal sound range with which we usually deal. It is within this range that we find the levels of speech and the sounds we find harmonious, such as most music and most of the sounds of nature. Within this range are also the sounds that we find socially unacceptable or embarrassing, including those we hear through the walls from our neighbors, as well as bodily noises that we know people do not wish to hear. Mostly it depends on how our brains label these sounds. The more they are labeled as annoying, the more stress they are likely to create. Sensory fatigue is another form of stress which occurs with a constant unwanted noise, especially if repetitive. Think of the sound of a dripping faucet during the night and you’ll get the idea.

Danger levels of noise are those at which our ears can be damaged with prolonged exposure, particularly if the sound remains at a single frequency. Such levels of noise can cause permanent damage to our ears, but are rarely encountered in domestic circumstances (except when listening to music too loudly with headphones).

Most solutions to noise problems that occur in our homes fall under one of the following four strategies:

• Avoid making noise that causes annoyance to others, which usually means controlling a noise at its source.

• Reduce noise that travels from one part of the house to another, to give greater privacy and reduce annoyance.

• Reduce noise from neighbors that is transmitted through a shared (“party”) wall.

• Reduce noise from external sources such as road or air traffic.

Sources of Noise

Perceived Decibels

Jet engine at 100-foot distance

Pain threshold — loud thunder

Large amplifier speakers at 6-foot distance

Motorcycle engine at 6-foot distance

Heavy truck

Danger level if noise continuous

Vacuum cleaner

Normal conversation

Inside average home

Refrigerator

Whispering

Swallowing

Rustling leaves

Hearing threshold

130-140

120

110

100

90

80

70

60

50

40

30

20

10

0

CONTROL OF NOISE IN YOUR HOME

In order to be able to begin controlling the noise in your own home, it is necessary to understand the various ways in which noise is created and transmitted.

Airborne Sound

Noise is most easily transmitted if there is an uninterrupted pathway from outside to inside the house—for instance, through open windows, gaps around doors, or even small cracks. To reduce airborne sound, it is simply necessary to seal gaps in the element that you wish to act as the sound barrier.

Impact Sound

This is the type of sound that is produced by the impact of shoes or furniture on floors, or by a masonry bit drilling into a wall. Heavy objects and hard surfaces produce the most impact sound, so by using soft-soled shoes and soft floor coverings, this type of sound can be greatly reduced.

Structure-Borne Sound

Impact sound is carried through the walls and floors of your home by the structure itself, which carries the vibrations and transmits them to various parts of the house. Structure-borne sound can be reduced by introducing discontinuities, such as a resilient layer of material. An example of this is the “floating floor’ where flooring is laid on resilient pads or matting, such as rubber underlay, in order to isolate the floor surface from the structure (see illustration). Noise from the use of stairs is a common structure-borne sound.

Panel Sound

This is a particular type of transmission that occurs when a whole partition or pane of glass is made to vibrate like a drum. It is most likely to occur with lightweight partitions. The transmission is also greatly increased if the noise has a frequency similar to the natural resonance (vibrating frequency) of the panel. This type of transmission can be reduced by increasing the weight of the partition in such a way as to damp the vibrations. Panes of glass can also act in this way, and in this case secondary glazing will reduce noise transmission considerably.

Reverberation

Reverberation occurs when sound is reflected backwards and forwards between hard-surfaced walls: a completely empty room, for example, has a particular hollow echo. Sometimes we like a room to have some reverberation, such as when playing music, or even when singing in the bath. However, it is normally more restful, especially with children, to have rooms that act to deaden the sound. This is usually easily achieved with soft furnishings such as carpets, curtains, and furniture.

Reducing Noise at Its Source

Theoretically, you have control over noises that emanate from within your own home. Examples of noises that people find annoying are those from garden or kitchen machinery, amplified music, noisy stairs, noisy plumbing, banging doors, or DIY construction. Some examples will help you to see that there is almost always something you can do to reduce any kind of noise, if you are prepared to do something about it.

A washing machine, for instance, produces:

• Noise directly from the machine itself

• Impact sound from vibrations on the floor; and

• Structure-borne sound from these vibrations.

The noise of the appliance itself can often be reduced by damping the metal panels making up the body of the machine. One way of achieving this is to glue rubber or foam to the inside of the panels, provided this does not interfere with the running of the machine. Alternatively, the machine could be partly or wholly enclosed to help isolate the sound.

The noise from the vibrations on the floor are helped by placing the feet of the washer on thick rubber bases to absorb the vibrations. If there is still a problem with structure-borne sound, the whole machine could be placed on an insulated pad to further isolate the vibrations from the main structure of the building.

Noisy stairs: The sound can be reduced by using a carpet or other covering with a resilient foam-rubber underlay.

Noisy plumbing: This problem can often be solved easily if the cause is correctly identified and action taken. If you can't do this yourself, find a plumber who is interested in dealing with such problems. It is often the result of too sharp a bend in a small pipe. Restraining vibrating pipes effectively can also help reduce the problem.

Banging doors can be prevented by installing weather stripping in the rabbet joint.

We can also exercise control over many aspects of the noise we ourselves produce, such as the volume of the music we listen to and the loudness of our voices.

Reducing the Transmission of Noise

The two most common examples of noise problems within a home are:

• Noise being transmitted through the floor to the room below

• Noise being transmitted through a lightweight partition to an adjacent room

Sound deadening for floors: Skirting fixed to wall only compressible strip to floor; Resilient layer (for example, old carpeting)

The most effective solution to the first problem is to lay a new floor, such as chipboard or plywood on top of a resilient underlay, making sure that the edges of the new floor do not contact the walls or skirting. A soft floor covering can be then laid on top of this new surface. This means of soundproofing is illustrated below.

The problem of reducing noise that is transmitted through a lightweight partition can be solved by increasing the effective weight of the partition. This can be done by adding a layer of drywall to the partition, fixed with an acoustic sealant to help damp the sound. Alternatively, fitted shelving or cupboards can be used to add weight.

Reducing Noise through a Shared (Party) Wall

This is the most difficult noise to deal with: it has already carried through a heavy party wall, and the measures applied to a lightweight partition will have little effect. However, the following measures should help:

• Check that there are no cracks in the wall, as these will tend to weaken the acoustic integrity of the wall.

• Apply all the measures that are appropriate for partitions (see above), such as adding a layer of drywall, fitted shelving, or cupboards.

• Use your social skills to negotiate a reduced noise level — and don’t give up!

Reducing Noise from External Sources

Noise from traffic and airports can be very wearing. The most important way that this sound is transmitted into the inside of the house is through the windows. To soundproof windows, you will need secondary glazing installed with a 6- to 8-inch gap between the two panes of glass.

Ensuring that all gaps are sealed is another important measure; you will also need to think out your ventilating system very carefully. It could be worth considering a full heat-exchange system (see DRAFT-PROOFING and VENTILATING).

Pleasurable Background Sounds

Creating our own pleasant sounds can have a powerful calming effect. If we produce these sounds when we are feeling stressed, we can induce a feeling of well-being and tranquility. If you live in the country, the natural sounds of birds singing, water bubbling, or leaves rustling may surround you anyway. However, if you live in a town, alternative sources can include a fountain, a hanging arrangement of tinkling shells, or specially produced tapes of natural sounds in order to mask an unpleasant background noise. These can all help provide a harmonious acoustic environment, reducing stress levels and promoting a sense of well-being.

PRIORITIES FOR ACTION

+ We can usually do something about all types of noise in our homes. It helps to first identify the source and method of transmission.

+ Be aware of when and how loudly you make noises that might annoy others, such as amplified music, loud conversation, DIY noise, etc.

+ If you have a problem with noise from the floor of a room in your house, consider introducing a floating floor using the method illustrated.

+ If you have a problem of sound being transmitted between adjacent rooms, you will need to increase the weight of the partition, either by adding a layer of drywall or by introducing built-in shelves or cupboards to add weight and help damp and absorb the sound.

+ Reduce noise from appliances such as washing machines by isolating the appliances on rubber or insulated pads.

+ If you find the quality of sound in your home a bit dead, or if there is annoying background noise, consider adding your own pleasurable sounds (see above).

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