LOCATING DEFECTS BY SOUND,
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THE DEOREE of noise made by vehicle or or engine when in motion is usually an indication of its mechanical • condition, and progress in design is often demonstrated by silent working.. In examining a vehicle for the wear of -moving parts, sound is of great import 'aura. By different types of knocks and -taps the trained :ear can locate undue wear or faulty parts, but it is sometimes difficult to isolate any -particular sound, as other, and possibly louder, sounds may deaden it.
In order:to trace any particular noise to its source, it has been the practice amongst mechanics and others to utilize a stick or piece of metal as a kind of stethoscope. -An zlaboration of this idea is to be :found in an instrument known asithe Sonoscope, and produced by the Capac Co., Ltd.., 2, Woodstock Street, Oxford Street; London, W. 1. This in.strtiment consists of a diaphragm, to the lower portion of which is secured a .test.ro0which can be used in one or more lengths. Above the diaphragm holder is a tube, bifurcatedqat its upper end and 'fitted with binaural attaehmpnts for the ears. The end, of the test rod is applied to the suspected parts until the sound is at a maximum. The user can then judge from' its nature the defect by which it is caused.
With this instrument only the sound of the particular part to which the instrument is applied is conveyed to the ears of the operator, all general noises bring ° excluded. For use on internal combustion engines, both on the C16
'bench. and during test on the road or track, the instrurnent is applied direct, and such defects as piston slap,' loose bearings, incorrect valve tappet clearance, defective cams, etc., can be traced with certainty to the actual part. For gearbox and back axle tests on the road while running, the instrument an :be attached to the part .under test by a' special bracket, whilst the, operator can remain in the vehicle, or even drive it, whilst noting the noises under actual conditions.
. The instrument, is made in various types, and-in order to enable comparison between various sOunds, a damping device has been introduced by which the sounds can either be compared with. each other or with some standard source of noise. TheType A Sonoscope,' with three-joint testing rod extending to 2 ft., is priced at 38s. 6d. The 'Type B, which
has special ear pieces and hinged spring head-band, is priced at 63s..
The actual method of utilizing the instrument' is as follows :—To locate a knock, connect the tubes, of the head piece and instrument, screw in one or more of the test rods in order to. bring the and of the instrument low enough to the point to be tested to suit the convenience of the" operator, and place the head spring over the ears with the ear plugs facing forward.
It should be noted that at the lowest end of the testing rods must always be positioned the plain, round-ended rod. Apply this rod to the suspected. part at three or four :points, well . separated, noting the position giving the loudest noise. This position having been found, the nature of the sound and. the knowledge of the construction of the part will assist in indicating any defects.