SME M2-9 Tonearm

SME engineers, recognising the potential of the latest complementary equipment, accepted the challenge to design and build a pick-up arm which unlike others in existence would make no detectable sound contribution of its own. The work took almost four years and the measure of its success is the acceptance of the Series V precision pick-up arm by technical experts and users as one of the world's truly great audio products.Series V sound has an almost startling dynamic range and neutrality enabling high levels to be enjoyed. It escapes the 'LP' sound and demonstrates that structural resonances in pick-up arms are responsible for much that makes vinyl records readily discernible from master tapes.

The functioning of a pick-up arm appears simple but is in fact very complex. All cartridges employ relative motion between armature and stator portions of a generating system to produce the signal output. Reproduction can only be true therefore when all movement representing groove modulation is made by the armature to which the stylus cantilever is attached and none by the stator represented by the cartridge body. Unless the pick-up arm holds the latter against even the minutest movement at audio frequencies the signal will be modified in some way. The result is a subtle loss of clarity, dynamic range and transient attack that can make the sound from even the best system tiring to listen to.

The following notes will help a better understanding of the problems and how they were resolved in this radically new design.

In common with any mechanical device the behaviour of a pick-up arm is governed by three properties of matter that also define the laws of motion. The first property is mass which opposes any change in motion. The effective mass of an arm and cartridge resists motion least at low frequencies but increasingly as frequency rises. It is this resisting force which makes the operation of a cartridge possible. At subsonic frequencies the armature and stator move as one allowing the slow movements needed to negotiate the record surface without generating a signal. At audio frequencies however the increased resisting force causes the armature to move relative to the stator and a signal is produced. The transition point between these two conditions is important for a clean low frequency response and is established by the compliance of the cartridge and the total effective mass of the arm and cartridge body.

The second property is stiffness which resists bending or flexing. It is a restoring force, proportional to position or deflection.

The third property is damping or resistance to motion. Here motion means velocity and without it there is no damping. The total equation of force acting on a pick-up arm is therefore the sum of three parts: acceleration acting on the mass, velocity acting on the internal or applied damping, and bending or deflection acting on the stiffness.



Mass and stiffness determine how much a pick-up arm will flex and vibrate and damping determines how long it will vibrate. Damping alone cannot prevent flexing or vibration, it can only lessen its effect. The stiffer the arm the less it will flex and vibrate; the more massive the less it will vibrate.

Very high tone arm mass would therefore be ideal to control the cartridge had it not to be strictly limited to preserve the required relationship of compliance and mass already referred to. Stiffness, the second part of the equation of force, must therefore be used also. Infinite stiffness would be ideal but we have to be more realistic. In a beam of given length stiffness is dependent on the material used, its cross-sectional area and in the case of a cylindrical beam increases as the cube of its diameter. Doubling the diameter will make it eight times as stiff.

Features & Specificatons of the SME Model 2 Tonearm