Speckle, although usually characterised as random noise, is a deterministic artefact that affects all kinds of signals that use coherent sources, such as acoustical waves (sound and ultrasound), laser or radar. In the context of ultrasound for non-destructive testing, speckle is responsible for a severe signal degradation leading to misdetection of the material inner structures, like flaws or microbubbles. On the other hand, in medical imaging, the presence of speckle may create a substantial level of subjectivity in the diagnostic. Many methods of speckle reduction are based on the premise that the speckle presence in a signal or image depends on the density of the acoustic scatterers randomly distributed in the material or tissue being investigated. On the contrary, in this paper we want to show that the signal-to-noise ratio of any signal or image corrupted by speckle does not change with scatterer density. Additionally, even a regular grid of scatterers may give rise to an acoustic signal that is corrupted by speckle with a random pattern. We will present results showing that the speckle presence is independent on the scatterer density or on any special distribution. We believe that the proper identification of speckle and its distinguishing from other kinds of noise and artefacts can help the characterisation of materials and may improve the performance of speckle reduction methods.5 41224129Burckhardt, C.B., Speckle in ultrasound B-mode scans (1978) IEEE Trans. Sonics and Ultrasonics, 25 (1), pp. 1-6Wells, P.N.T., Halliwell, M., Speckle in ultrasonic imaging (1981) Ultrasonics, 19, pp. 225-229Thijssen, J.M., Ultrasonic speckle formation, analysis and processing applied to tissue characterization (2003) Pattern Recog. Lett., 24, pp. 659-675Lizzi, F.L., Feleppa, E.J., Alam, S.K., Deng, C.X., Ultrasonic spectral analysis for tissue evaluation (2003) Pattern Recog. Lett., 24, pp. 637-658Dantas, R.G., Costa, E.T., Leeman, S., Ultrasound speckle and equivalent scatterers (2005) Ultrasonics, 43 (6), pp. 405-420Shankar, P.M., A model for ultrasonic scattering from tissues based on the K distribution (1995) Phys. Med. Biol., 40, pp. 1633-1649