Radial tracking, also known as linear tracking, refers to a turntable tonearm design that moves the cartridge in a straight line across a vinyl record. This movement directly mirrors the path taken by the cutting lathe that originally inscribed the grooves onto the master disc. The goal of this design is to maintain a consistent and accurate relationship between the stylus and the record groove from the beginning to the end of playback. This contrasts with more common pivoted tonearms, which swing in an arc across the record surface.
The Problem of Tracking Error
The majority of turntables utilize pivoted tonearms, where the stylus travels in an arc across the record. This arc-like motion inherently introduces tracking error. This error occurs when the cartridge angle deviates from the true tangent of the record groove at any given moment during playback.
This angular deviation means the stylus is not perfectly aligned with the groove walls. Such misalignment can cause measurable distortion in the audio signal, affecting the balance between the left and right channels and leading to a less accurate stereo image. The distortion can become more noticeable as the stylus moves closer to the center of the record, where the groove’s wavelength becomes smaller.
Another consequence of this angular error in pivoted tonearms is “side-thrust” or “skating force.” As the stylus moves through the groove, the friction created pulls the tonearm toward the center of the record. This uneven pressure can lead to imbalanced wear on the record grooves and the stylus over time.
How Radial Tracking Works
Radial tracking tonearms eliminate tracking error by moving the stylus in a straight line across the record, precisely replicating the motion of the cutting lathe. This design maintains the cartridge at a consistent 90-degree angle to the record groove throughout playback.
Achieving this linear movement involves various mechanical principles. Many radial tracking tonearms employ a servo system where sensors detect minute deviations from the ideal tangential path. If the arm moves slightly off-tangent, these sensors trigger a small electric motor to advance the tonearm carriage along a rail, bringing it back into perfect alignment.
Other designs, such as air-bearing tonearms, achieve extremely low friction, allowing the stylus to guide the tonearm passively across the record. These systems use a cushion of air to support the tonearm, enabling smooth movement without mechanical resistance. Some older designs, like those from Harman Kardon, used a rotating drive-shaft with an angled runner wheel to maintain alignment.
Benefits of Radial Tracking
Radial tracking systems offer several advantages in vinyl playback by minimizing tracking error. By maintaining a constant 90-degree angle between the stylus and the record groove, these systems reduce angular distortion, leading to a more accurate and detailed sound reproduction.
The elimination of side-thrust, or skating force, is another benefit. Since the stylus is always aligned tangentially to the groove, there is no inherent tendency for the tonearm to pull towards the record center. This means radial tracking turntables do not require anti-skating adjustments, which can be a compromise in pivoted designs.
This consistent alignment and balanced force distribution contribute to improved channel separation and more precise stereo imaging, as both groove walls are read simultaneously and evenly. Reduced side-thrust also helps preserve the record grooves and the stylus, extending their lifespan by minimizing uneven wear.
Practical Considerations
While radial tracking offers advantages, practical considerations exist. Their mechanical complexity, often involving motors, sensors, and precise bearing systems, makes them more expensive to manufacture than conventional pivoted tonearms. This complexity can also lead to higher maintenance requirements and greater susceptibility to issues if not properly cared for.
Setup and calibration of radial tracking turntables can be more involved. While they eliminate the need for anti-skating adjustments, achieving precise alignment of the linear tracking mechanism can be a delicate process. Some designs, especially those with air bearings, may require an external air pump, adding to the system’s footprint and potential noise.
Despite these considerations, advancements have made radial tracking turntables more reliable and accessible than earlier models. The market for these systems remains smaller than for pivoted turntables, and finding replacement parts or specialized servicing can be more challenging.