A folded pendulum consisting of the sum of a conventional compound pen
dulum and an inverse pendulum can be tuned to create a pendulum with t
he dynamic response of a kilometre scale pendulum. Results are present
ed demonstrating the stability and Q-factor of the system down to a re
sonant frequency of 17 mHz. It can be scaled up to form a pre-isolatio
n stage in the vibration isolation system for laser interferometer gra
vitational wave detectors.