Turntables, Arms & Cartridges

Incorporated in 1993, California's Minus K Technology operates at the sharp end of industrial and scientific vibration control. Laboratories carrying out critical laser experiments, high resolution microscopy or other imaging, or NMR spectroscopy with huge, super-cooled magnets, all need to be very mindful of how the smallest of external vibrations will impact on the performance of these often very large instruments. Costly active isolators typically employ slaved sensors and actuators to mitigate incoming vibration – active noise cancellation – while passive 'air suspension' tables, using bladders and pumps, have also been a common go-to solution for heavyweight industrial isolation.

Minus K's solution is passive and elegantly 'tuneable' but side-steps the potentially noisy pump of a pneumatic platform for what it describes as a negative-stiffness mechanism (NSM). In its ultimate form this technology would comprise three isolators stacked in series: a tilt-motion isolator on top of a horizontal-motion isolator on top of a vertical-motion isolator. For a turntable only the vertical and horizontal isolators are employed – the former taking the form of a stiff spring whose compliance can be adjusted, according to the mass placed atop, by either compressing or relaxing the spring from below. This is the function of the 'Suspension' wheel that sits proud of the Helix Two Mk3's top-plate and allows the springs' compliance to counter the weight above (no more, no less, hence the phrase 'taking the stiffness out of the spring').

In practice the low ~0.5Hz suspension frequency is achieved by the flexure of thin metal supports from which this spring assembly hangs – it is these flexures or cantilevers, not the support spring, that sets the compliance of the suspension. Horizontal isolation, typically at 1.5Hz and above, is achieved by a series of beam columns – flexible rods – that connect between the top (load) and bottom (spring) plates. Readers can learn more from Minus K's own video https://www.youtube.com/watch?v=m9J8-YAMQKo. PM