Centroid SG Integrated Tonearm Manual
Thank you for your purchase of the Spiral Groove Centroid SG Integrated Tonearm. The Centroid
SG Integrated model is designed for use with with Spiral Groove turntables. As the name implies,
some functions, such as the arm lift, anti-skate support, and fluid damping, are integrated into the
Spiral Groove armboard. The Centroid Universal Integrated model is designed for use with all
other turntables and many of the arm mounting details are different in procedure than those
outlined in this manual. The discussion of the tonearm design below provides much useful
information for both model tonearms, but can be read before or after the installation and setup of
the tonearm. Those with some experience, and who are eager to get listening, may want to skip
directly to the setup procedures outlined on page 5, which will guide you easily to superior results.
Enjoy!
The Centroid unipivot tonearm
The Centroid tonearm design effort had two main goals. The first, and most obvious: to design a
tonearm that provides the best mechanical and electrical conditions for a phono cartridge to
transmit the signal from a record with the greatest fidelity and lowest noise. The second goal, and
one less frequently considered: to provide the simplest and most consistent means of setting up the
arm and cartridge in order to fully realize the performance capabilities designed in to the arm. As
a result, the Centroid is able to realize the greatest performance benefits in the greatest number of
turntable systems than any previous tonearm. The beauty of the design – its inherent elegance –
allows the basic elements to be understood in fairly simple terms.
A few words about the Centroid’s design...
The Centroid evolved from a holistic approach called Balanced Force Design™, which focuses on
preventing mechanically induced resonances from adversely affecting the music signal by
modulating the moments of inertia and in effect balancing the forces involved during playback.
Moment of inertia can be described as a body's resistance to angular acceleration. In the case of a
tonearm, the lower the resistance, or moment of inertia, the more effortlessly the cartridge is able
to respond to the normal record warps and the basic conditions of disc playback.
It might be easiest to think about the influence of these forces on the arm/cartridge system by
imagining holding a broom at the end of its handle, farthest away from the head or bristles. Your
ability to move the broom under precise control will be very difficult. The moment of inertia in
this case is high. The closer you move your hand to the head of the broom, the easier it is to
control, because the moment of inertia is being lowered. At a certain point, the broom will be
balanced at the center of the mass, or the centroid. At this point, the broom head is easiest to
control, because the moment of inertia is at its lowest.
The dynamic forces involved in controlling a broom during even the heaviest sweeping are not
nearly as complex as those found in the process of tracking of a microscopic record groove. In
order to achieve a similar level of control for a tonearm under those conditions, many unique,
even patent pending, features have been developed for the Centroid tonearm.
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