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BLOG 'A chronology of soundproofing systems London'
Noise, Sleep and Health:
Sleep is a biological necessity, and disturbed sleep is associated with a number of health problems.
Noise disturbs sleep by a number of direct and indirect pathways. Even at very low levels physiological reactions (increase in heart rate, body movements and arousals) can be reliably measured.
Based on the systematic review of evidence produced by epidemiological and experimental studies, the relationship between night noise exposure and health effects can be summarized as below.
| Average night noise level over a year Lnight,outside: | Health effects observed in the population: |
| Up to 30 dB |
Although individual sensitivities and circumstances may differ, it appears that up to this level no substantial biological effects are observed. Lnight,outside of 30 dB is equivalent to the no observed effect level (NOEL) for night noise. |
| 30 to 40 dB | A number of effects on sleep are observed from this range: body movements, awakening, self-reported sleep disturbance, arousals. The intensity of the effect depends on the nature of the source and the number of events. Vulnerable groups (for example children, the chronically ill and the elderly) are more susceptible. However, even in the worst cases the effects seem modest. Lnight,outside of 40 dB is equivalent to the lowest observed adverse effect level (LOAEL) for night noise. |
| 40 to 55 dB | Adverse health effects are observed among the exposed population. Many people have to adapt their lives to cope with the noise at night. Vulnerable groups are more severely affected. |
| Above 55 dB | The situation is considered increasingly dangerous for public health. Adverse health effects occur frequently, a sizeable proportion of the population is highly annoyed and sleep-disturbed. There is evidence that the risk of cardiovascular disease increases. |
Inside/Outside Differences:
Night-time environmental noise affects residents mainly inside their homes. In order to protect residents inside their homes from noise from outside sources, attention should be focused on windows since they are generally the weakest points in the sound propagation path. Roofs must also be considered with regard to aircraft noise. There are many types of window in the EU, varying from single thin panes within frames without additional insulation, to four-pane windows within insulated frames.
The simplest types of facade have a sound reduction (from outside to inside) of usually less than 24 dB, and the most elaborate facades (built to cope with cold climates, for example), have sound reductions of more than 45 dB. In central Europe, most windows are double-glazed, mounted in a rigid and well-insulated frame. Their range of sound reduction is between 30 dB and 35 dB when closed.
Background Level:
A simple definition of background level or “ambient noise” level is the noise that is not targeted for measurement or calculation. Background noise can interfere with the target noise in a number of ways. It can:
- – mask the signal
- – interact physically
- – interact psychologically.
As this report is often dealing with low-level target noise, masking is an important issue. Masking, however, is a complex process. The human auditory system is uncannily good at separating signals from “background”.
The rule of thumb that a noise can be considered masked if the signal is 10 dB below the background is only valid if the noises have the same frequency composition and if they actually occur at the same time. This is particularly important to stress where LAeq levels are compared: even a relatively continuous motorway of 50 dB cannot mask aircraft noise of 30 dB, because this may be composed of five aircraft arriving at an LAmax of 57 dB. Neither can birdsong, because the frequency domains do not overlap.
Another factor relevant for this report is that background levels are lower at night time than they are in the daytime. This is true for most man-made noises, but also for the natural background levels as wind speeds at night slow down.
Most levels mentioned in this report do not take background levels into account – explicitly. Where long-term LAeq levels are related to effects like hypertension and self-reported sleep disturbance, background levels are ignored, but they could obscure the effect at the lower end of the scale. This then influences the lowest level where an effect starts to occur.
In sleep laboratory studies the background level is kept as low as possible, around 30 dB. The background of the instrumentation is 20 dB.
In semi-field experiments it has been found that background noise levels inside bedrooms are very low, partly because people tend to choose their bedrooms on the quiet side of the building. This may have the side-effect of exposing children to higher levels.
Protection Measures and Control:
What is the best strategy to reduce sleep disturbance? The first thought should always be to reduce the impact, either by reducing the number of events or by reducing the sound levels, or both. For some effects reducing the number of events may seem to be more effective (although that depends on the exact composition). Other effects are reduced by lowering overall noise level by either the number of events, the levels per event or by any combination.
In combination with other measures, sound insulation of bedroom windows is an option, but care must be taken to avoid negative impact on inside air quality. Even then, many people may want to sleep with their windows open, thereby making the insulation ineffective.
Exposed areas could be a good choice for uses such as offices, where there will be no people at night, or where it is a physical impossibility to sleep with the windows open (fully air-conditioned buildings, for example hotels and sometimes hospitals).
A simple measure is the orientation of noise-sensitive rooms on the quiet side of the dwelling (this applies to road and rail traffic noise).
Zoning is an instrument that may assist planning authorities in keeping noise-sensitive land uses away from noisy areas. In the densely populated areas of the EU this solution must often compete, however, with other planning requirements or a simple lack of suitable space.
