Understanding Acoustic Emission Testing- Reading 1 Part B-A

As a practical matter, the maximum distance between piezoelectric
transducers, or between the transducers and the source of the acoustic
emission event, should not be very large. Berthelot and Robert required an
array of transducers arranged in a 40-cm square mesh to locate acoustic
emission events reasonably accurately. They found that for ordinary concrete,
with a fifth transducer placed in the center of the 40 x 40-cm square mesh,
only about 40% of the events detected by the central transducer were also
detected by the four transducers at the corners; with high strength concrete,
this proportion increased to 60 to 70%. Rossi also found that a 40-cm square
mesh was needed for a proper determination of acoustic emission events.
Although more distant events can, of course, be recorded, there is no way of
knowing how many events are “lost” due to attenuation. This is an area that
requires much more study.