Instrumentation for geognostic investigation
The principle of the sonic tests on masonry is the same as principle of Ultrasonic Pulse Velocity on concrete.
The only difference is the method to produce the longitudinal elastic wave used for the measurement: a hammer is used instead of an ultra-sonic pulse.
The frequencies thus produced (a few hundreds of Hz), lower than those of the ultra-sounds (a few tens of KHz) are able to also cross scarcely compact masonry walls, such as brick-faced or brick walls, thus allowing to evaluate the conservation state, through the speed and/or mitigation values of the wave produced.
This type of test can also be applied on concrete structures, which sizes do not allow to use ultra-sounds, because these can no longer be measured at a few metres from the source. The sonic tests give less accurate values compared to the tests with ultra-sounds, but they can be performed also on scarcely compact materials and/or at a distance of a few metres.