Noise Control for Landscape Design

Paskal WandaWesley CheruiyotJonathan Chirchir

IntroductionBasic Definitions

Sound Control - Design and control techniques for the elimination or reduction of unwanted sound in a landscape.

Sound - waves generated by any pulsation or vibration of a source . The surrounding air is disturbed, thereby causing pressure changes which can be heard .

Noise - Any unwanted sound. Frequency - The rate of repetition of these sound waves is referred to as frequency . It is measured in cycles per second or units of hertz (Hz) . The normal audible range for humans is 20 to 20,000 Hz.

Sound Pressures and Decibels - Although the human ear acts like a sound filter by discriminating against some frequencies and giving preference to others, the range of sound pressure which the human ear can detect is relatively broad. Given this broad range, the measurement of sound is made more convenient by use of a logarithmic scale called the decibel (dB) scale .

TYPICAL SOUND OCCURANCES OF EVERYDAYWeakest sound that can be heard - 0 (db)Rural area at night - 25 (db)Conversation at 1meter - 60 (db)Jet taking off at 50m - 120 (db)anything after this may now become painful to the receiver.

Understanding the Issues involved

Because sound control is a vast subject the information presented here is naturally very limited and is a basic stepping stone one should make an effort to understand the physics of sound and the complexity involved in gathering data prior to sound control design.The science of sound control in the landscape involves much more than the simple quantification of data . The quality of sound may be as important as the quantity of sound. Some sounds can have profound psychological effects on people . For example, the constant drone of cars on a highway is rarely as offensive as the squealing of brakes at an intersection .Psychological Response to Sound

Although the acceptability of the type and level of noise is highly subjective, noise often disturbs people by interfering with communication, sleep, and other everyday activities . Noise can also cause physical discomfort and, if intense enough, can cause damage to hearing.

People are usually annoyed more by high-frequency sound than by low-frequency sound, by certain tonal qualities (e .g ., whines, hisses, or squeals), by impulsive sound (e .g ., bangs and clanks), and by intermittent sound . Any frequent or continuous exposure to noise can lead to a reduction of human efficiency by a deterioration of physical and emotional well-being.

Approaches to Sound Control

Two approaches to sound control in the landscape include acoustical planning, where potential noise problems are minimized during design stages, prior to any construction, and retrofitting, where noise problems are mitigated by alteration to existing developments.

Acoustical PlanningWhere acoustical planning is possible, setbacks and other methods can be employed to minimize sound transmissions. Acoustical planning should be part of any land use planning project, especially with such major projects as airports, highways, and railroads . Acoustical models should be developed and tested to assess the planning implications both on and off the property.

Acoustical planning is more desirable than retrofitting, because as potential noise problems are identified, cost-saving mitigative measures can be taken to reduce noise levels to acceptable standards while at the same time designing a physical landscape with improved visual qualities .

This can be achieved, for instance, through grading concepts that retain significant natural landforms and existing vegetation, as well as incorporate noise buffer mounds where necessary . Preplanning can accommodate public and private interests by reducing noise to acceptable levels, while retaining landscapes of high quality.Grading - Work of ensuring a level base or one with a specific slope for construction work.

• Road noise is not just blocked but now absorbed and no longer just reflected to the other side!

• Soundproofing for noisy generators here is incorporated in the initial design as they are being installed

This are good example of Acoustical planning. All Weather Sound Panels (Sound proofing panels) built by Acoustiblok an American firm based in Orlando.

Retrofitting:Acoustical planning principles can also be effectively applied to existing development,

but the aesthetic results are often unattractive . Establishing adequate rights-of-way or buffer zones is difficult, typically including architectural barriers or walls .

Capital construction and eventual maintenance costs can become limiting factors .

Acoustical Variables

1. Source of the sound.

2. The path and distance of the transmission of the source.

3. The receiver of the sound.

This is a good example of retrofitting. It may impact on the visual outcome given that it has literally killed a view. But at this stage the sound proofing needs must outway the aesthetic desires in a sense. This is referred to as Noise Reduction Fences. Acoustifence does extraordinarily well in not only blocking sound but also producing far less reflective sound than solid walls do. It is easily installed or removed in less than one hour. Totally NON-mold and UV tolerant, this material is virtually indestructible and does a wonderful job as a sound barrier.

images courtesy of http://info.acoustiblok.com

Noise Measurement

No single method or process exists for measuring occupational noise. Hearing safety and health professionals can use a variety of instruments to measure noise and can choose from a variety of instruments and software to analyze their measurements. The choice of a particular instrument and approach for measuring and analyzing occupational noise depends on many factors, not the least of which will be the purpose for the measurement and the environment in which the measurement will be made.

Sound Level Meter

The sound level meter is the basic measuring instrument for noise exposures. It consists of a microphone, a frequency selective amplifier, and an indicator. At a minimum, it measures sound level in dB.

Noise Dosimeter

Measuring noise with a sound level meter is relatively simple when the noise levels are continuous and when the worker remains essentially stationary during the work shift. A noise dosimeter is preferred for measuring fluctuating noise exposure when the noise levels are varying or intermittent, when they contain impulsive components.The noise dosimeter may be thought of as a sound level meter with an additional storage and computational function.

NOISE ESTIMATIONS ANDCALCULATIONS

To assess the potential impact of noise from a proposed major facility such as a new highway or airport expansion, noise levels must be predicted. This involves taking into account major noise contributors like major traffic highways. This is then followed actual site test of noise levels which involves interviews on site of the impact on noise.

Traffic NoiseNoise generated by traffic depends on:1 . Volume2. Mix (e .g ., cars and trucks)3. Speed4. Road characteristics (e .g ., gradient and surface) Noise propagated to a receiver depends on :1 . Distance from traffic2. Type of ground3 . Height of receiver 4. Amount of shielding5. Height of source

Just as a reminder the physics of sound prediction is extensive and one must take a keen interest on this in order to do a good sound control analysis. They are some very useful computer programmes that are used in sound control. Not forgetting they are conventional methods that involve the use of some machinery like the sound level meter.

CONTROL OF NOISE OUTDOORS

Measures to control noise can be divided into three categories, each of which can be addressed in a noise control strategy. These are : 1 . Source of the sound2 . Path and distance of the sound transmission3 . Receiver of the sound

Source of the SoundNoise can be reduced at the source either by architecture or equipment modification . In some instances the amount of noise generated is so great that it is rarely cost-effective or feasible to abate the noise at the source . In such cases a combination of other acoustical control measures may be required .

Path and distance of the sound Noise can be attenuated by increasing the distance between the source and the receiver and/or by introducing noise screening .Sound BarriersThe degree of attenuation provided by a noise barrier is mainly a function of

(1) the diffraction angle a through which the sound path must

be bent in order to get from source to receiver and (2) the frequency of the sound source

Five main factors that influence the acoustic effectiveness of a barrier are: (1) distance (offset), (2) height, (3) continuity, (4) length, (5) mass.An additional factor influencing the acoustic effectiveness of a barrier is the sound absorption capability of the barrier, i .e., the degree to which it minimizes reflection of sound .Distance (Placement of Barrier):A sound barrier should be erected as close as possible to either the noise source or the receiving position in order to maximize the diffraction angle Height of Barrier:The minimum height of the barrier should be such that the line of sight between source and receiver is interrupted

Distance as a variable influencing theeffectiveness of a noise barrier. Barriers should be placed tomaximize the diffraction angle.

Height as a variable influencing the effectivenessof a noise barrier. Barriers should be placed to interruptlines of sight.

Continuity of Barrier:No gaps or holes should be present in a noise barrier. It must be effectively airtight.

Length of Barrier:As a guideline, the length of a noise barrier should be at least 1 to 2 times the distance between the barrier and the protected structure to minimize sound diffraction around the ends of the barrier.

Physical Mass of a Barrier (Material):To minimize sound passing through a barrier, it should have a surface weight, or mass, of at least 6 to 12 kg/m2 A noise level reduction of 10 to 15 dB(A) is possible with such a barrier however, a reduction of 5 to 10 dB(A) is considered to be more cost-effective .

Earth Berms

The careful design and situation of earth berms can be an effective way of reducing noise from traffic or construction operations Berms can either be temporary or remain as a permanent feature of the landscape (Figures 660-9 and 660-10) . The slope of a berm depends on the type of surface treatment or maintenance involved . For instance, a mowed grass berm is easier to maintain if graded to a slope of 1 :3 or less .

Barrier Walls and Earth BermsBarrier walls can be used separately or in combination with earth berms to minimize noise levels (Figure 660-11) .

VegetationThe type of ground surface over which sound travels does have a substantial effect on sound attenuation, particularly when traveling over large distances . Areas covered with grass or other types of groundcover are more absorptive than hard, paved surfaces, which tend to reflect the sound . Taller plantings, such as hedges or shallow screen plantings (even though they may completely block the view of the noise source), will not significantly reduce actual noise levels .However, dense plantings of trees with an understory of shrubs can result in a reduction of 3 to 5 dB(A) per 30 m (100 ft) of depth from the sound source (Figure 660-12) .

Vegetation can be used to barrier the effects many problems including noise pollution. As with plantings for wind or visual barriers, the selection and arrangement of the plant material is key to a successful outcome.. With these barriers vegetation serves to soften the visual effect of the barrier and reduce the reverberation of sound. Earthen berms are often used in combination with trees and shrubs to deflect and absorb sound when the available space is limited (example 2). Vegetation alone can be used where adequate space is available. To be effective the planting must be multiple rows to about 40-75' in depth. Care also must be taken to plant the first row at 50' from a roadway or any area that should not be subject to extra snow deposits. Conifers or evergreen broadleaf plants will naturally provide the best year around noise reduction. Deciduous trees and shrubs can be added to the planting for variety and added summer noise reduction (example 3). Vegetation should be selected for site conditions with special attention to issues of air pollution and salt spray if used near busy roadways. See urban tolerance chart. It is also important to incorporate fast growing plants and long lived plants for a quick and long lasting barrier.

Building Layout and Site Selection

Specially constructed noise barriers are expensive, but fortunately are not the onlymeans available for noise control . Other means available include :1 . The use of existing or proposed buildings to shield others that are moresensitive2 . The use of natural or constructed landscape features (hills and valleys,earth berms, etc.)3 . The optimization of other site planning or design criteria (discussed in 7 .0, which follows)

•Upgrade the windows and doors. The most expensive option is to replace all windows and doors with sound proof models. These windows and doors are thicker and more effective than regular ones at reducing noise levels. The other option is to install a special soundproofing insert inside the window. These inserts are still clear, and are made to reduce noise effectively. Remember that all your windows, both parallel and perpendicular to the road, must be altered for full benefit.•5 Use a fountain or other water feature to mask the noise. The sound of water is relaxing, and a great way to reduce traffic noise that is low.

DESIGN PRINCIPLES IN NOISE CONTROLDesign Criteria

The three most important criteria for noise barrier design are acoustic effectiveness, economic feasibility, and visual attractiveness .

Acoustic criteria include the site planning objectives, the choice of barrier material, and the quality of construction . Economic criteria include the cost of materials and labor, implementation ease, and operating and maintenance costs . Visual criteria include environmentally acceptable alternatives for highway users as well as for people who have to live near the barriers .

The design of noise barriers should incorporate both the functional requirements and the aesthetic preferences of all who are affected . In the case of a highway, for instance, both the actual users of the highway as well as the users of adjacent lands are factors to consider. They should integrate well with the existing landscape and promote feelings of security and comfort for both drivers and passengers .

Aesthetic Issues

Noise barriers along highway corridors should be seen as elements which define and enclose linear space. Visual perception in these corridors will be influenced by:

Travel speed, light, spatial quality, location, physical distances, roadway characteristics, and viewing height, all modified by the basic design elements of planes, mass, and texture .

Planes :Planes are an important element in noise barrier design . In highway design, for instance, where minimal rights-of-way exist, barriers can provoke feelings of excessive enclosure or give a monotonous appearance . In such circumstances, it is necessary to create variety and interest in the design of the barriers and related landscape by changing the textures, choosing different materials, using color, and articulating the forms.

A combination of vertical and horizontal lines in a wall (i.e. articulation of texture rather than monolithic mass) can create the apparent height of the wall

MASS:Mass refers to the form and shape of a barrier. Massive, unrelieved forms can sometimes arouse uncomfortable feelings of insecurity

(Figure 660-14). The apparent mass of a noise barrier can be minimized by means of stepped wall sections, staggered alignments, plantings,

A wall which steps back can open up the view for the motorists and open up psychological relief from feelings of tight enclosure

The apparent mass of a noise barrier can be minimized by means of stepped wall sections, staggered alignments, plantings, shadow lines or reveals, color variation, articulation of form, and integration with landform

Wall design and plantings can be composed to provide interesting visual sequences along highway corridors

Fine-textured walls are often monotonous, and may cause reflective glare

Texture:Texture is a visual, surficial quality referring to the extent of detail of a material or design

Coarse textured walls minimize reflective glare and provide visual diversity along highways.

Increased speed of travel, angle of vision, and distance from an object all tend to decrease the apparent degree of texture . Surfaces that are relatively smooth (I .e, fine textured) not onlycause undesirable reflections of light and sound but also promote monotony in the landscape

MAINTENANCE CONSIDERATIONS

Ease of access, intrusion on adjacent property owners, durability of materials, minimum cost, ease of replacement, and visual appearances are the major considerations .

Earth BermsThe development of earth berms as noise barriers requires the manipulation of landforms and the stabilization of the soil. New grading should blend into existing landscape as much as possible. Slopes should not exceed 1 :3 for ease of grass cutting and equipment access. Groundcovers other than grass may be used ; they usually require less maintenance.

Low maintenance ground covers for earth berms. Long term self maintaining natural plant communities can be used as low-maintenance ground covers for earth berms.

Recently, there has been an increased use of various groundcovers, shrubs, and trees in an attempt to provide a long-term, self-maintaining natural plant community, although the initial maintenance requirements can be higher.

Long term self-maintaining plant communities can be used as low maintenance ground covers for earth berms

The maintenance implications of noise barrier walls include such basic considerations as access to both sides of the barriers and access to possible cutoff land . Design complexity, quality control during construction, and the choice of materials to minimize damage and abuse are factors that will affect long-term maintenance costs . As with berms, the location and alignment of noise barriers require study in order to prevent or reduce problems of snow drifting across roadways and walks, etc .

BARRIER WALLS

Time saver standard standards for landscape architecture.www.wikipedia.comInfo.acoustiblok.comwww.howthingsaredone.com

References