A type of acoustic logging tool that uses a large number of receivers, typically 4 to 12. Modern acoustic logging tools are designed to measure not only the compressional wave but also the shear and other acoustic waves generated by the transmitter. The separation and identification of these waves are facilitated by the use of an array of receivers placed about 6 in. (15 cm) apart, which is close enough to avoid aliasing but far enough to sample a significant moveout in the wave. The waveforms at each receiver are recorded and processed by signal processing techniques, such as slowness-time coherence, to measure the velocities of the different waves.