What Sound Characteristics should a Good Tonearm Have?

Good question, should a tonearm sound at all? Should it appear superficially and put its bass or treble stamp on it? There are certainly a few playing possibilities on the part of the manufacturer, but the majority of the effects are created by the interaction with the mounted pickup.

Do we like it at all when a tonearm tries to “sounder”? No. From our point of view, the tonearm has one central task above all: it must guide the mounted cartridge and at the same time give it the necessary freedom, while not itself becoming sonically apparent and above all resonating as little as possible. In order for the tonearm to be able to guide the cartridge consistently, its effective mass must fit the cartridge and it must be able to adapt to it by means of the finest adjustment possibilities. And of course the bearings must be of the highest quality.

Compliance: why the compliance of the needle suspension affects the sound.

Compliance indicates how hard or soft the suspension of the needle carrier is, which in turn supports the scanning diamond. The unit of measurement of compliance is µm/mN. It is measured, and this is where it gets exciting, at 10 Hz – most of the time. Some measure at 100 Hz, especially Audio Technica. And the value is already 1.5 to 2 times higher than the specification in the brochure. In addition, especially with Audio Technica, that – for whatever reason – the compliance data often looks quite different in practice, even with correct interpretation. With a measuring plate, it doesn’t get any more precise than that. Why this is so: quite honestly, we don’t know, but the experiences are also worth something.

In addition, there is the distinction between dynamic and static compliance. Dynamic counts; and you get it if you divide the static value by two. Very roughly, bean counters will certainly find numerous objections, because the specified contact force also plays into it – but we simply don’t care about that at this point.

Our basic rule for compliance

(slightly different interpretations/limits are common and legitimate, but also not decisive, more on this later)

• Low compliance = hard suspended systems = values between 6 and 12 µm/mN
• Medium compliance = medium-hard/medium-soft suspended systems = values between 11 and 22 µm/mN
• High compliance = soft suspended systems = 22 to 30 µm/mN
• Very high compliance = very soft suspended systems = 30 to > 40 µm/mN

Tonearms can be roughly classified according to the following scale

(here, too, there are logically “floating” limits)

• Ultra-light tonearm: 4 to 5 grams
• Light tonearm: 6 to 9 grams
• Medium-heavy tonearm: 9 to 15 grams (most arms in use today)
• Heavy tonearm: 19 to 24 grams
• Very heavy tonearm: 25 grams and more

Important: for tonearms with interchangeable headshells, always include the headshell.

Tonearm and pickup as a mass-spring system

The values/divisions mentioned are important because the combination of tone arm and pickup represents a spring-mass system. Like all classical spring pendulums, such a combination has a natural frequency that depends on the hardness of the spring and the mass of the overall system. This is the famous “moving mass”, and only this is decisive: If the hardness of the spring increases (i.e. at lower compliance), the resonant frequency increases. If, in turn, more mass is added, the resonant frequency decreases.

The excitation of the mass-spring system and the consequences

What happens if you excite this mass-spring system with its natural frequency? Logically: it resonates, so that the oscillation builds up extremely. These oscillations in turn superimpose other frequencies. They lead to interference or droning and color the sound image or limit the exact reproduction of the music. For example, if the resonant frequency were 40 Hz and you were playing a nice Kraftwerk record, your needle might do a dance and bounce out of the groove.

The “right” resonant frequency for tonearm/cartridge combination.

Derived from the 40 Hz example, one might conclude that the resonant frequency should be as low as possible, and then be “inaudible.” Unfortunately, there are other troublemakers in the frequency cellar:

• The natural resonance of subchassis players (e.g. some Thorens models), whose platter board is spring-loaded. Depending on the model, the natural frequencies of subchassis players are usually in the range of 2 Hz to 5 Hz. So pushing into this range is counterproductive.
• The groove of the record itself. The groove itself is not exactly round – especially with our great new pressings. This means that groove noise and thus interference waves are generated during playback. Engineers at Shure have conducted a study on this and found that 70% of such waves are below 5 Hz and 95% below 8 Hz. This makes it clear why the resonance frequency should not slip too far down even with board players or mass drives.
• Excitations by impact sound: one should not dance around like Rumpelstiltskin in front of the turntable anyway; nevertheless it is not good if the needle becomes unsteady due to frequency excitations over the floor.

Thus, over time, a “rule of thumb” emerged that the resonance frequency should be between 8 Hz and 12 Hz, so as not to negatively excite the tonearm / cartridge with either low-frequency music signals or wavy records.