Damping dilution factor for a pendulum in an interferometric gravitationalwaves detector

Mechanical loss in pendulums is a subject of great importance to gravitatio nal waves detectors being built and being planned, as this determines the l evel of thermal noise associated with the detector suspensions. Relationshi ps between the mechanical loss of the pendulum and the mechanical loss of t he suspending fibres or wires can be derived in two apparently contradictor y ways which give answers different by a factor of two. In this paper the d ifferences are resolved and it is shown that both methods lead to the same answer. (C) 2000 Elsevier Science B.V. All rights reserved.