Abstract: An attenuator for use in attenuating tube waves in a borehole includes a body formed from a permeable material having a rigid matrix which can be saturated with fluid. In its simplest form, the attenuator is one or more cylindrical bodies as part of a borehole acoustic logging system. Alternatively, the shape, particularly at the end regions, can be modified to reduce the amount of reflection of tube waves in the borehole. Another attenuator includes a body for placement in a borehole formed from an attenuating material, the shape of the body being selected such that the change in impedance experienced by acoustic waves in the borehole is gradual rather than abrupt. One particularly preferred shape for the body comprises one in which the diameter is greatest towards the center of the body, for example the shape formed by two cones placed base to base, or a cylinder having conically tapered ends. A number of bodies can be used where appropriate.