. Basic methods for the calibration of sonar equipment. 152 PRODUCTION TESTING OF SONAR TRANSDUCERS PROJECTOR HYDROPHONE -H 'RE 1. Optimum test geometry in a simjjlc icctant;iilai' tank without liafflcs designed foi a gi\cn lest distance and reflection path length. a PROJECTOR. OPAQUE BAFFLE FitURF, 2. Arrangement of baffles in a rectangular tank for the iruerccplion ol principal reflections. placed in such a way as to intercept the reflection from the side of the tank. One possible arrangeineiit of baffles is shown in Figure 2. This procedure cannot be used to eliminate reflections, but
. Basic methods for the calibration of sonar equipment. 152 PRODUCTION TESTING OF SONAR TRANSDUCERS PROJECTOR HYDROPHONE -H 'RE 1. Optimum test geometry in a simjjlc icctant;iilai' tank without liafflcs designed foi a gi\cn lest distance and reflection path length. a PROJECTOR. OPAQUE BAFFLE FitURF, 2. Arrangement of baffles in a rectangular tank for the iruerccplion ol principal reflections. placed in such a way as to intercept the reflection from the side of the tank. One possible arrangeineiit of baffles is shown in Figure 2. This procedure cannot be used to eliminate reflections, but it will increase the effective path length between them. 84 CHOICE OF SECOND TRANSDUCER The choice of the second transducer to be used in the acoustic production test measurement depends in general on the instrument under test. For receiving response measurements the second transducer must be a sound source, and vice versa. Its res])onse should be fairly uniform over the fretiuency range being in- vestigated, so that it responds i apidly to acoustic and electric transients; that is, the time constant of the second transducer should be small if it is to be used in pulse testing. Also, if its response is uniform, slight inaccuracies in frequency will not cause appre- ciable errors. The transducer should be fairly stable and show only small changes in response with tem- perature. For continuous-wave noise or warble measure- ments, the transducer should be directional. This will help to discriminate against reflections coming from directions other than that of maximum sensitivity. However, since at a given frequency greater directi\- ity can be obtained only by increasing the size of the transducer, there will be a certain maximum direc- tivity beyond which it will be impossible to go. Fur- thermore, the proximity effects increase with trans- ducer size. The NDRC 6B standard projector will be a suit- able transducer for most of the cases encountered. Any other transducer with simil
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