Noise Control for LandscapeDesignPaskal WandaWesley CheruiyotJonathan Chirchir
Introduction Basic DefinitionsSound Control - Design and control techniques for the elimination or reduction of unwanted sound in alandscape.Sound - waves generated by any pulsation or vibration of a source . The surrounding air is disturbed, therebycausing 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 cyclesper 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 againstsome frequencies and giving preference to others, the range of sound pressure which the human ear candetect is relatively broad. Given this broad range, the measurement of sound is made more convenient byuse 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 involvedBecause sound control is a vast subject the information presented here is naturally verylimited and is a basic stepping stone one should make an effort to understand the physics ofsound 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 simplequantification 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 constantdrone of cars on a highway is rarely as offensive as the squealing of brakes at an intersection . Psychological Response to SoundAlthough the acceptability of the type and level of noise is highly subjective, noise oftendisturbs people by interfering with communication, sleep, and other everyday activities . Noisecan 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, bycertain tonal qualities (e .g ., whines, hisses, or squeals), by impulsive sound (e .g ., bangs andclanks), and by intermittent sound . Any frequent or continuous exposure to noise can lead toa reduction of human efficiency by a deterioration of physical and emotional well-being.
Approaches to Sound ControlTwo approaches to sound control in the landscape include acoustical planning, wherepotential noise problems are minimized during design stages, prior to any construction, andretrofitting, where noise problems are mitigated by alteration to existing developments.Acoustical PlanningWhere acoustical planning is possible, setbacks and other methods can be employed tominimize sound transmissions. Acoustical planning should be part of any land use planningproject, especially with such major projects as airports, highways, and railroads . Acousticalmodels should be developed and tested to assess the planning implications both on and offthe property.Acoustical planning is more desirable than retrofitting, because as potential noise problemsare identified, cost-saving mitigative measures can be taken to reduce noise levels toacceptable standards while at the same time designing a physical landscape with improvedvisual qualities .This can be achieved, for instance, through grading concepts that retain significant naturallandforms and existing vegetation, as well as incorporate noise buffer mounds wherenecessary . Preplanning can accommodate public and private interests by reducing noise toacceptable levels, while retaining landscapes of high quality.Grading - Work of ensuring a level base or one with a specific slope for construction work.
This are good example of Acoustical planning. All Weather Sound Panels (Sound proofingpanels) built by Acoustiblok an American firm based in Orlando. • Road noise is not just blocked but now • Soundproofing for noisy generators absorbed and no longer just reflected here is incorporated in the initial to the other side! design as they are being installed
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 Variables1. 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 MeasurementNo single method or process exists for measuring occupational noise. Hearing safety and healthprofessionals can use a variety of instruments to measure noise and can choose from a varietyof instruments and software to analyze their measurements. The choice of a particularinstrument and approach for measuring and analyzing occupational noise depends on manyfactors, not the least of which will be the purpose for the measurement and the environment inwhich the measurement will be made.Sound Level MeterThe sound level meter is the basic measuring instrument for noise exposures. It consists of amicrophone, a frequency selective amplifier, and an indicator. At a minimum, it measuressound level in dB.Noise DosimeterMeasuring noise with a sound level meter is relatively simple when the noise levels arecontinuous and when the worker remains essentially stationary during the work shift. A noisedosimeter is preferred for measuring fluctuating noise exposure when the noise levels arevarying or intermittent, when they contain impulsive components.The noise dosimeter may be thought of as a sound level meter with an additional storage andcomputational function.
NOISE ESTIMATIONS AND CALCULATIONSTo assess the potential impact of noise from a proposed major facility such as a new highwayor airport expansion, noise levels must be predicted. This involves taking into account majornoise contributors like major traffic highways. This is then followed actual site test of noiselevels 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 OUTDOORSMeasures to control noise can be divided into three categories, each of which can beaddressed 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 ofother acoustical control measures may be required .Path and distance of the soundNoise can be attenuated by increasing the distance between the source and thereceiver and/or by introducing noise screening .Sound BarriersThe degree of attenuation provided by a noise barrier is mainly afunction of(1) the diffraction angle a through which the sound path mustbe 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 capabilityof 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 positionin order to maximize the diffraction angleHeight of Barrier:The minimum height of the barrier should be such that the line of sight between source and receiver isinterruptedDistance as a variable influencing the Height as a variable influencing the effectivenesseffectiveness of a noise barrier. Barriers should be of a noise barrier. Barriers should be placed to interruptplaced to lines of sight.maximize the diffraction angle.
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 thebarrier 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 to12 kg/m2 A noise level reduction of 10 to 15 dB(A) is possible with such a barrier however, a reductionof 5 to 10 dB(A) is considered to be more cost-effective .
Earth BermsThe careful design and situation of earth berms can be an effective way of reducing noisefrom traffic or construction operations Berms can either be temporary or remain as apermanent feature of the landscape (Figures 660-9 and 660-10) . The slope of a bermdepends on the type of surface treatment or maintenance involved . For instance, amowed 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 noiselevels (Figure 660-11) .
VegetationThe type of ground surface over which sound travels does have a substantial effect on soundattenuation, particularly when traveling over large distances . Areas covered with grass or othertypes of groundcover are more absorptive than hard, paved surfaces, which tend to reflect thesound . Taller plantings, such as hedges or shallow screen plantings (even though they maycompletely 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 3to 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 manyproblems including noise pollution. As with plantings forwind or visual barriers, the selection and arrangement ofthe plant material is key to a successful outcome.. With these barriers vegetation serves to soften thevisual effect of the barrier and reduce the reverberationof sound. Earthen berms are often used in combinationwith trees and shrubs to deflect and absorb sound whenthe available space is limited (example 2).Vegetation alone can be used where adequate space isavailable. To be effective the planting must be multiplerows to about 40-75 in depth. Care also must be takento plant the first row at 50 from a roadway or any areathat should not be subject to extra snow deposits.Conifers or evergreen broadleaf plants will naturallyprovide the best year around noise reduction.Deciduous trees and shrubs can be added to theplanting for variety and added summer noise reduction(example 3).Vegetation should be selected for site conditions withspecial attention to issues of air pollution and salt sprayif used near busy roadways. See urban tolerance chart.It is also important to incorporate fast growing plantsand long lived plants for a quick and long lasting barrier.
Building Layout and Site SelectionSpecially 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, whichfollows) •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 acousticeffectiveness, economic feasibility, and visual attractiveness . Acoustic criteria include the site planning objectives, the choice of barriermaterial, and the quality of construction . Economic criteria include the cost of materials and labor, implementationease, and operating and maintenance costs . Visual criteria include environmentally acceptable alternatives forhighway users as well as for people who have to live near the barriers . The design of noise barriers should incorporate both the functionalrequirements and the aesthetic preferences of all who are affected .In the case of a highway, for instance, both the actual users of the highwayas well as the users of adjacent lands are factors to consider. They shouldintegrate well with the existing landscape and promote feelings of securityand comfort for both drivers and passengers .
Aesthetic IssuesNoise barriers along highway corridors should be seen as elements which define andenclose linear space. Visual perception in these corridors will be influenced by: Travel speed, light, spatial quality, location, physical distances, roadwaycharacteristics, 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, forinstance, where minimal rights-of-way exist, barriers can provoke feelings ofexcessive enclosure or give a monotonous appearance . In such circumstances, it is necessary to create variety and interest in thedesign of the barriers and related landscape by changing the textures, choosing different materials, using color, and articulating theforms.
A combination of vertical and horizontal lines in a wall (i.e.articulation of texture rather than monolithic mass) can create theapparent height of the wall
MASS:Mass refers to the form and shape of a barrier. Massive, unrelieved forms cansometimes arouse uncomfortable feelings of insecurity (Figure 660-14). The apparent mass of a noise barrier can be minimized by means ofstepped 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 barriercan be minimized by means ofstepped wall sections, staggeredalignments, plantings, shadow linesor reveals, color variation,articulation of form, and integrationwith landform Wall design and plantings can be composed to provide interesting visual sequences along highway corridors
Texture:Texture is a visual, surficial quality referring to the extent of detail of a materialor design Fine-textured walls are often monotonous, and may cause reflective glare
Increased speed of travel, angle ofvision, and distance from an object alltend to decrease the apparent degree oftexture . Surfaces that are relativelysmooth (I .e, fine textured) not onlycause undesirable reflections of lightand sound but also promote monotonyin the landscapeCoarse textured walls minimize reflectiveglare and provide visual diversity alonghighways.
MAINTENANCE CONSIDERATIONSEase of access, intrusion on adjacent property owners, durability ofmaterials, minimum cost, ease of replacement, and visualappearances are the major considerations .Earth BermsThe development of earth berms as noise barriers requires the manipulationof 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 equipmentaccess.Groundcovers other than grass may be used ; they usually require lessmaintenance.
Low maintenance ground covers for earth berms. Long term self maintaining natural plant communities can be used aslow-maintenance ground covers for earth berms.
Recently, there has been an increased use of variousgroundcovers, shrubs, and trees in an attempt to provide a long-term, self-maintaining natural plant community, although theinitial maintenance requirements can be higher.Long term self-maintaining plant communities can be used aslow maintenance ground covers for earth berms
BARRIER WALLSThe maintenance implications of noise barrier walls include such basicconsiderations as access to both sides of the barriers and access topossible cutoff land .Design complexity, quality control during construction, and the choice ofmaterials 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 studyin order to prevent or reduce problems of snow drifting across roadwaysand walks, etc .
References Time saver standard standards for landscape architecture.www.wikipedia.comInfo.acoustiblok.comwww.howthingsaredone.com