ASME B56.11.5:1992 pdf download POWERED AND NONPOWERED INDUSTRIAL TRUCKS
point and end point as established by the vehicletravel path.
A substantially level open space of not less than165 ft (50 m) radius, of which the central area of 33ft (10 m) radius, consists of concrete, sealed asphaltor similar hard material, free from any soft covering,shall be deemed to satisfy the requirement,but asmaller area may be used if it meets the requirementsfor hemispherical divergence.
NOTE:In practice, any departure from the so-called”idea””arises from four main causcs:
(a) sound abaorption by the surface of the grounds
(b) reflections from objects such as buildings,trees,or persons;(c) ground which is not of uniform slope over a sufficient area;(d) wind; care shoud be taken that gusts of wind do wmot affeea
results of the measurements.
lt is Impractical to specify in detail the effect pro-duced by each of these influences. It is consideredimportant, however,that the surfacc of thc groundand hard surface specifically within the measurementarea be free from snow, grass, loose soil, ashes, stand-ing water, etc.
To minimize the effect of reflection. it is furtherrecommended that the sum of the angles subtendedat the position of the test truck by surrounding build-ings within a 165 ft (50 m) radius, shall not excced90 deg. and that there be no substantial obstructionswithin the radius of 100 ft (30 m) from the truck. SeeFig.1.
Sites located between parallel walls should beavoided due to the effect of acoustical focusing. The presence of bystanders may appreciably influ-ence the meter reading if such persons are in thevicinity of the truck or microphone. No person otherthan the operator shall be in the opcrator stationarea of the truck.All bystanders shall be excludedfrom the test site.
5.3 Background Noise
5.3.1 The ambient sound level，including windnoise, due to sources other than the truck being mea-sured should be at least 10 dB below the lowestsound level generated by the machine being testedduring the work cycle.
5.3.2 If the differencc between the A-wcightedsound level measured with the sound source,thetruck operating，and the ambient sound level aloneis less than 10 dB, corrections for the influence ofbackground noise shall be made in accordance withthe following table:
5.3.3 If, when testing at an outdoor location, it isdetermined that the wind speed in the vicinity of the
truck and microphone is in excess of 2 mph (1 m/s),a windscreen around the microphone shall be used.Also, appropriate compensation for the effect of thewindscreen shall be allowed in calibration of the re-cording instrumentation.
5.4 Environmental Conditions
All instruments employed in the making of soundmeasurements shall be used in accordance with theelectrical andenvironmental conditions recom-mended by the manufacturer.
5.5Operator
5.5.1 The operator shall be in the usual drivingposition. No observers shall be in close proximity tothe driver or truck or in the cab (when provided)during the taking of measurements.
5.5.2 Observers shall be remote from and behindthose microphones in use during the specific test.5.5.3 Operators shall nor wear abnormally soundabsorptive clothing.A “hard hat” may be worn, how-ever, no hat,scarf,or bulky jacket which might influ-ence the sound measurements shall be worn.
In those tests where the microphone is positionedat a point 2 in. (50 mm) measured laterally, from theoperator’s ear. only the mounting frame or shoulderharness for the microphone shall be used.
ASME B56.11.5:1992 pdf download
