Discussion Articles

The importance of the pickup arm

 

 

I am determined to prove that the arm plays a fundamental role in the overall performance of the vinyl playback system. A first step is this article.

 

Traditionally, and still today, the turntable has been considered the main component of the analog system. Most of the design and artistic efforts have been directed to this component and still today is the center of most attention.

 

Then there is the cartridge, a tiny piece of equipment which is regarded as a sort of black box, a mystery component surely in part because of the “hidden” secrets inside of it. It seems to me that many audiophiles see them as crafted to possess specific sound character and qualities, as musical instruments. Nearly every analog fanatic has thoughts of upgrading to a better cartridge, as they have a big influence in the character of the sound reproduction - after all they are transducers!

 

Finally, the most underestimated component in the system is the tonearm (I would rather call it pickup arm and that is the term I prefer to refer to my arm for reasons explained here). It is generally seen as a simple link between the cartridge and the turntable, holding the cartridge in the right position relative to the groove, having practically no effect on the final reproduction. Well, that is the idea - the arm should not have any effect on the sound reproduction - but unfortunately the vast majority have a very significant effect! Even the SAT has it ;-)

 

The great majority of audiophiles believe the turntable plays a leading role on the sound reproduction compared to the arm. Consequently, they get as good a turntable as they can afford and do not put as much attention and budget into the arm. I am going to tell you why this is not objectively what makes more sense, once we have reach a decent level of performance and quality in the turntable and the arm.

 

 

First, it is fundamental to understand that the turntable and arm are purely mechanical systems (we do not consider the drive here) and are solely governed by the laws of Physics that apply to Mechanics. Still there are many designs and designers that ignore the laws and create atrocities.

 

The forces generated while the stylus is reading the groove, are equally applied to the vinyl record and to the stylus - equal and opposite forces. The forces applied to the record will affect the system record-platter, while the ones applied to the stylus will affect the system cartridge-arm.

 

Turntables , by their nature, are several times bigger and more massive than the arms sitting on them. They can actually be made very massive without negatively affecting their performance -it significantly improves if the mass is correctly used.

 

On the other hand, arms cannot be made nearly as massive as their turntable counterparts, because they need to be moved - linearly or pivoting- by the forces caused by the deflection of the cartridge minute suspension system. These forces are small and limit the mass the arm can have in order to be able to accelerate fast enough to follow the groove.

 

The forces applied to the turntable side will induce an acceleration of the system record-platter- provided the record is firmly hold against the platter and move as one solid. This is why it is so important to use clamping/hold-down systems for accurate sound reproduction. If there are some areas of the record not touching the platter, the record itself will be the main mass the forces will act upon, thus inducing much higher acceleration and movement of the record under the action of the stylus.

 

 

 

 

 

 

 

 

Massive platters present high inertia and rigidity to the forces trying to accelerate it and deform it, which translates in smaller deflections and therefore improved conditions for the cartridge to read the groove.

 

When these same forces in the opposite direction are applied to the cartridge-arm system, the situation becomes more compromised because of the small mass and dimensions of the components affected. What the cartridge is enduring under these circumstances isn’t short of amazing - I will not go into detail in this article. For now, is enough to accept the forces will go through the cartridge and be applied to the headshell. These forces will accelerate the arm and cause deflection of its structure.

 

Now compare the equivalent mass of the arm at the stylus point -the effective mass- with that of a massive platter. We are talking about 10-30g for the arm and 6.000-40.000g for the platter. That is a 1:1000 ratio!

 

This accounts only for the acceleration caused by the forces acting on both systems. The deflection - deformation of the bodies- will be dependent on the rigidity of each component. The platter has great advantage here as it can be made very thick with stiff and heavy materials; this makes possible and easy to design platters and turntables of great rigidity, but very difficult to even get closer to those levels with an arm.

 

Acceleration and deflection in the record-platter and cartridge-arm systems will generate distortion as the stylus will not exactly reproduce what is in the groove. Therefore, it is of outmost importance to keep accelerations and deflections to a minimum.

 

It becomes much more clear now how much tougher conditions, compared to the turntable, the arm has to work in and why very few arms are really designed to cope with them. An improvement in the mechanical performance of the arm will have much bigger effect in the sonic performance of the system than a comparable improvement in the turntable. This is because the platter-turntable are already much more rigid and massive by default than even the most massive and rigid of the arms - doubling the rigidity of the arm will yield a substantial improvement, while doubling the rigidity of the already much more rigid and massive turntable will only have a slight effect.

 

The arm is potentially responsible for far more distortion than it is the turntable. An improvement in the performance of the arm has a bigger effect on the overall reproduction accuracy of the system.

 

 

 

Turntables are comparatively easy to design and manufacture to get quite good results, which explains why there are so many brands and models, many of them doing a good job. Pickup arms are much more difficult to engineer and manufacture to achieve very good results and have an enormous effect on the reproduction accuracy; this is why there are so few arms which can be considered really good or exceptional. With that said, exceptional turntables require very good engineering and manufacturing skills too, as do cartridges, but we are talking exceptional!

 

 

Disclamer: this is not intended to be a scientific article; I try to keep it strict and accurate without being heavy to read. It does not cover the whole system and interaction between components. Nevertheless, this does not change the outcome!

 

 

Marc Gomez

2013-12-12

 

Upcoming articles:

 

  • More performance for your money

 

 

  • Why I am using industry-reference design & manufacturing tools

 

 

  • Dynamically balanced arms

 

 

  • Arm geometries and alignment geometries