Dr. Analogue's Corner

Taking the Tone Out of the Tonearm – Part Two

By September 15, 2017 No Comments

Having the best bearings in the audio world is no guarantee of ideal tonearm performance if they are loaded asymmetrically. For this reason, our starting point should always be an arm tube which is parallel to the vinyl record surface. Traditionally one would adjust parameters such as stylus rake angle (SRA) or vertical tracking angle (VTA) by raising or lowering a tonearm’s bearing housing. In so doing, listeners would hear a definite sonic difference but not for the reasons they might expect and it would certainly never represent an optimised result. It is for this reason that the AQUILAR and AXIOM tonearms, along with the removable arché headshell, allow one to adjust not just the overhang and alignment but also the SRA, VTA, and azimuth at the cartridge mounting point but without compromising the rigidity which is essential for effective transfer of mechanical energy.

Another critical aspect of any tonearm is its geometry. All pivoted tonearms, with the notable exception of designs from Swiss manufacturer Thales which solve one problem while creating what is arguably a far more objectionable one, describe an arc across the record. At two so-called null points the stylus will be perfectly tangential to the groove. Tracking distortion at these null points is zero and rises to maxima on either side of them. The position of the inner and outer null points is determined by a combination of tonearm offset angle, overhang, and effective length. A by-product of the offset angle and the amount of groove friction is a skating force which pulls the arm towards the inner groove.

Only one geometry was conceived with modern 12” stereo records in mind and that is the UNI-DIN curve from Dietrich Brakemeier of Acoustical Systems. Unsurprisingly, his AQUILAR and AXIOM tonearms were specifically designed to showcase this unique geometry. Notably, the UNI-DIN curve features less skating force, significantly gentler distortion gradients, and much lower distortion towards to the most challenging inner groove area. The sonic result is one of more headroom during dynamic musical passages, particularly towards the inner groove area; an overall more relaxed and natural sound with greater stability of musical images within the soundstage. Any good recording of piano music will immediately illustrate the superiority of the AQUILAR and AXIOM’s UNI-DIN geometry.

Just a brief note on linear tracking tonearms which, theoretically, maintain perfect tangency between the stylus and record groove at all points but in practice represent a host of other, more serious, mechanical compromises.

While not intended as an exhaustive essay covering every aspect of tonearm design we hope that you have gained some insight into the key physical aspects and design choices which dictate a tonearm’s sound, or ideally, its lack of any identifiable sonic character. We also hope that you have a better understanding as to why the Acoustical Systems AQUILAR and AXIOM tonearms are the least compromised, and by extension the most optimised, tonearm designs currently available on the market. But please do not take our word for it. Instead, give the team at Audio Fidelity a call or send us an email to arrange a listening session and judge the sonic results for yourself.

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