Tonearm Effective Length
Effective length is the straight distance from a tonearm’s pivot, the point it rotates around, to the stylus tip. It is usually specified in millimetres.
Measure between those endpoints, not along a curved arm tube or from the counterweight. Nominal labels such as “9-inch” describe a size class; use the exact effective-length figure for geometry.
Tonearm Effective Length — Tonearm
For a conventional pivoted arm with positive overhang, effective length equals mounting distance plus overhang. Mounting distance runs from the pivot to the platter’s centre spindle. Overhang is how far the stylus extends beyond that spindle when aligned with the pivot and spindle.
For example, 222 mm mounting distance plus 14.5 mm overhang gives 236.5 mm effective length. These are example dimensions, not universal settings. Follow the exact arm manufacturer’s alignment specifications and template. Position the arm mount using its specified mounting distance, not its effective length.
Tonearm Effective Length — Turntable
On a turntable, the figure belongs to the fitted arm, not the deck’s dimensions. Check the arm and configuration actually supplied. After changing the cartridge, use that arm or turntable manufacturer’s alignment guide to restore the correct stylus position.
A replacement arm also needs the correct mounting distance and mounting pattern, with room for arm and counterweight movement and the lid. Effective length alone establishes neither physical fit nor a sound-quality ranking.
Sources
- AT-CAP1 User Manual — Audio-Technica
- RB330 Technical Specifications — Rega
- RB330 Instructions — Rega
- AS-212R — Ortofon
- AT-LPA2 User Manual — Audio-Technica