"That [sand-filled tonearm] may have contributed to the findings of Stereophile founder J. Gordon Holt, who first wrote about the WT Tonearm in 1984, and who declared that Firebaugh's tonearm was the first in his experience to prevent the average moving-coil cartridge of the day from sounding bright, overly aggressive, and altogether unlistenable. More important, JGH suggested that the reason for the improvement was no mere euphonic distortion, but rather that the WT Tonearm did a better job of preventing unwanted resonant energy from adding its gritty fingerprint to the sound."
That JGH was a pretty bright man.