Theory of Operation
Nimbus isolates G&D Transforms CD Transport in system w/ JC-1s driving Rockport Syzygy speakers, CTC Blowtorch preamp and Entec Number Cruncher DAC as well as BBQ amp and Bybee filters, not to mention Rockport Capella Turntable w/ Clavis DC.
Sub-Hertz Performance
Machina Dynamica's Nimbus Sub-Hertz Platform is a unique, 6 degree-of-freedom isolation device with extremely low resonant frequencies - as low as 0.5 Hz. Nimbus is capable of not only isolating the component from "large-scale effects" such as footfalls and traffic-generated vibration that might cause a stylus to jump out of the record groove, but of improving analog and digital playback well beyond expectation - even in the absence of footfalls and traffic. Nimbus' sonic performance in the absence of large scale effects illustrates the profound impact of the Earth's crust movement, frequently ignored, or at least trivialized, on sound quality. Nimbus' unusual design characteristics are examined in the following paragraphs.
Floppiness and Instability
What makes Nimbus so effective in dealing with seismic type vibration? There are a number of reasons -- Nimbus' very low resonant frequency for one, plus a few less-obvious ones. Nimbus is the only pneumatic isolation platform in the world to employ a single air spring. This approach minimizes Nimbus resonant frequencies and maximizes the number of directions of isolation. Virtually all other pneumatic isolation devices employ 3 or 4 air springs/bladders for stability and simplicity; however, tripling the number of air springs/bladders triples the system spring rate, siginifcantly raising resonant frequency. (Note: A single bicycle inner tube is sometimes used to construct an isolator. While providing good stabilty, the inner tube has a very non-ideal geometry for the purpose - i.e., high contact surface area/volume ratio.) Lateral stiffness for the tall, thin and floppy Firestone air spring is achieved only by incorporating both a coil spring lateral support system and a ballast weight system (to lower the system center of gravity). As a consequence of the single air spring (unipivot) design, Nimbus isolates the component in all 6 directions of motion - the vertical direction, all horizontal directions, and all three rotational directions (around the x, y and z axes) and achieves resonant frequencies as low as 0.5 Hz. The resonant frequency in the vertical direction is around 2 Hz, in the horizontal plane around 1 Hz. Conventional pneumatic devices are simpler to construct and can support more weight than Nimbus; however, they represent a considerable compromise in performance. Much lower spring rates - thus lower resonant frequencies and higher performance - can be obtained with the single air spring approach, assuming the lateral support problem can be solved.
Seismic Vibration, a Brief Recap
Seismic vibration is a general term for very low frequency vibration produced by the constant movement of the Earth's crust, but can include virbation produced by traffic, subways, wind, tides, etc. Seismic vibration affects all electronic and mechanical elements of audio components and is quite deleterious to the sound quality. Most of the energy of seismic vibration is in the frequency range 0-10 Hz, with peaks around 1 Hz or lower. Unfortunately, most isolation devices, pneumatic and otherwise, are relatively ineffective for the very lowest frequencies of vibration because their resonant frequencies are simply too high. Recall that isolation cannot occur for vibration with frequencies below the device's resonant frequency and that vibration with frequencies above the resonant frequency are subject to the gradual attenuation behavior of the mechanical low-pass filter.
% Transmission and Resonant Frequency
The majority of sesimic energy is in the frequency range 0-10 Hz; unfortunately, the resonant frequencies of nearly all isolation devices (outside of certain laboratories) aren't low enough to be all that effective for vibrations in this critical 0-10 Hz range. For example, an isolating device with resonant frequency of 3 Hz can't isolate the component from vibrations with frequencies below 3 Hz because attenuation of vibration doesn't begin until 3 Hz. Furthermore, the 3 Hz device is only partially effective for vibration in the 3-10 Hz range due to the gradual slope of the mechanical low-pass filter function -- % transmission of vibration at 10 Hz is about 12%, while % transmission at 5 Hz is about 50%! By contrast, Nimbus' % transmission at 10 Hz is around 1-3% and at 5 Hz around 5-10% for most directions. Furthermore, most other isolation devices are not free to move in all 6 directions, due to constraints in their design, which further limits their performance.
A Wave Travels Under it
What are the "Directions of Motion" and why are they important? The Earth's crust movement (and other low frequency vibration generators like subways, buses, tides, wind, etc.) produces powerful mechanical waves that travel horizontally over the Earth's surface, a lot like shaking out a rug or waves traveling on the surface of the ocean. Imagine a boat on the ocean with a wave traveling under it. The wave forces the boat to move up and down, but also pushes the boat to and fro, or side to side (horizontal motion). Depending on the direction of the wave, it also causes the boat to "pitch" or "roll" or "twist" (rotational motion). The vertical, horizontal and rotational forces of a wave are illustrated below.
Two! Two Isolation Systems in One! - The Pendulum and Gravity Feedback Loop
Nimbus' "unipivot" (single air spring) design has a number of interesting characteristics perhaps not obvious at first glance. The Nimbus subchassis consists of the top plate/component and lower plate/ballast + connecting rods; this subchassis behaves like a pendulum, with its pivot point at the top of the Firestone air spring. The 25 lb ballast on Nimbus' lower plate is the pendulum mass. The pendulum behavior of the Nimbus subchassis serves to isolate the component in the horizontal and two rotational directions, supplementing the isolation characteristics of the Firestone air spring/mass system. A characteristic of this pendulum isolator is that the force of gravity acts as a feedback loop to damp the motion of the pendulum subchassis - when seismic vibration (some percentage naturally makes it up through the mass/spring isolation stage) forces the subchassis to move ever so slightly away from its equilibrium position, the force of Earth's gravity on the 25 lb Ballast Mass acts to restore the subchassis, including the component, to its equilibrium position. Thus, Nimbus can be viewed as a "semi-active" isolation device, with the Earth's gravity acting as the "semi-active" restoring force for the pendulum system.
World's Best Air Spring
The Nimbus uses the World's Best air spring, made by Firestone. This air spring possesses ideal geometry and physical characteristics. This Firestone air spring is a convoluted type (folds within itself) that has a thick fabric that will not leak over time. The thin rubber "fabric" of air bladders in most other pneumatic devices allows the pressurized air to leak directly through it over time, requiring more frequent air replenishment and affecting sonic performance as the system continually readjusts for lower and lower internal air pressure and uneven pressures in the bladders/air springs. An extra-large auxiliary air reservoir is fitted to the Firestone air spring to reduce spring rate and improve Nimbus' isolation effectiveness. The single air spring design completely avoids an important but overlooked problem of other air spring/bladder isolation systems -- the multiple air springs/bladders interfere with each other. Sesimic vibration forces some of the air springs/bladders to compress, which in turn forces the others to expand, ad infinitum. This mutual interference causes "pumping" in the pneumatic system and is quite audible compared to Nimbus. Nimbus produces sound that is supremely dynamic, extended and transparent compared to most other isolation devices.
Lateral Support System
Ballast weight on the Nimbus lower tray is required to obtain sufficiently low center of gravity for the system, given the "floppy" nature of the Firestone air spring, even when pressurized. A complex lateral support coil spring system provides additional lateral support (stiffness) for the Firestone air spring/auxiliary reservoir and acts as an isolating device itself (for horizontal directions). Ballast is 25 lb steel barbell weight, symmetrical in shape with very high stiffness.
What on Earth to Isolate?
Nimbus is intended for CD and SACD players, DACs, turntables, amps, preamps up to about 35-40 lb. All components should be isolated for optimum system performance. Machina Dynamica also designs and sells other isolation devices (Promethean and Nirvana) that are intended for heavier components or where space is a consideration.
The "Machina Dynamica Sound"
Nirvana Base, like other Machina Dynamica isolation stands, has a profound influence on the sound. "Digititis" effects of digital systems are virtually eliminated, with dramatic improvement to signal to noise ratio and dynamic range. Cymbals and other percussive instruments are presented with great solidity and weight, with lack of glare and grain. Bass performance is taut, supple and very dynamic.
Prices
Nimbus Sub-Hertz Platform, clear finished high grade maple with set of 3 Super DH Cones for mounting and high quality air pump $700. Black version $800. Ballast weight not included, customer procures one 25-lb CAP brand flat (Standard) barbell weight.