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Environmental Acoustics
Environmental acoustics is defined as:
'The science of outdoor sound, its sources, and its propagation in both natural and urban environments'. (Christopher L. Morfey, Dictionary of Acoustics)
Noise that prevails under normal conditions in an environment is known as 'ambient noise'. The sources and levels of ambient noise typically vary with the type of environment and time of day. Typical sources of environmental noise include:
Many planning authorities will permit a new development to emit relatively high noise levels into the environment so long as the noise is not detrimental to people. However, projects are sometimes forced to comply with environmental noise control standards even when the only land affected is vacant. Occasionally, a project may be required to control noise near locations where endangered animal species are present.
For proposed projects that are expected to generate significant noise levels, excessive noise should be anticipated and dealt with during the planning process. Projects may be required to control noise emitted into the environment by:
Apply noise controls to reduce noise to a level deemed 'less than significant' as part of an Environmental Impact Report (EIR) noise analysis or other noise study
Designing the project to comply with existing local, state or federal noise limits
Monitoring noise levels after construction and applying additional noise control as necessary
For proposed projects that are expected to generate significant noise levels, excessive noise should be anticipated and dealt with during the planning process. Projects may be required to control noise emitted into the environment by:
Environmental Noise Mitigation
Methods to mitigate and control noise in the environment depend on the type of noise source and the severity of the noise levels. For industrial noise sources, engineering and administrative controls are effective ways to reduce the sound. With the use of noise modeling, noise consultants can specify maximum noise levels for individual pieces of equipment or design barriers and enclosures to block noise transmission paths.
The reduction of transportation noise can be problematic due to the inability to mitigate noise at the source. For road traffic noise, barriers can be placed alongside the roadway to control noise at external areas. As a general rule of thumb, a roadway barrier will reduce traffic noise by approximately 1 decibel for every foot of height. For situations where the noise must be controlled at indoor locations, buildings can be designed to incorporate acoustically upgraded walls, windows and ventilation systems to reduce transmission into the building.
Music from bars and clubs can be particularly annoying to nearby residents due to its repetitive 'beating' nature; however, this is not the only noise source associated with these facilities. The noise made by patrons walking to and from bars is a common complaint of people living nearby. The problem is exacerbated by the fact that the noise is typically made when during the evening and nighttime hours. Control of environmental noise produced by bars and clubs is often difficult when the building has not been designed to incorporate noise control measures from the start. Administrative controls such as placing limits on the hours of operation can be effective. Some clubs also place limiters on the audio feed to the speaker system so as to prevent the sound exceeding a pre-defined level. The best way to prevent noise problems caused by bars and clubs through an effective zoning policy whereby clubs are not permitted within a buffer zone around the residences.
Residential noise is usually controlled through enforcement of local noise ordinances in one of two ways:
Common noise sources and A-weighted noise levels
| Noise Sources | A-Weighted Sound Level (dBA) | |
|---|---|---|
| Commercial Jet Take-off (200 ft) | 120 | |
| Pile Driver (50 ft) | 110 | |
| Ambulance Siren (100 ft) | 100 | |
| Diesel Truck (150 ft) | 90 | 10 dB change generally perceived as twice or half as loud |
| Garbage Disposal (3 ft) | 80 | |
| Vacuum Cleaner (5ft) | 75 | 5 dB change generally perceived as quite noticeable |
| Passenger Car, 65 mph (25 ft) | 70 | |
| Air Conditioning Unit (50 ft) | 65 | 3 dB change is generally barely perceptible |
| Normal Conversation (5 ft) | 60 | |
| Light Traffic (100 ft) | 50 | 1 dB change is generally not noticeable |
| Bird Calls (distance) | 40 | |
| Soft Whisper (5 ft) | 30 |
If you want further consultation about environmental noise control issues that may be affecting you or
have already decided to take action and would like the sound tested and
analysed contact Noise Monitoring Services today on (323) 546-9902
. As a company of engineers with advanced degrees in acoustical engineering, we can offer sound
measurement and monitoring and consulting on any source and measurement of noise.
