Various objective tests of the legendary Acoustic Research AR-XA turntable demonstrating its stellar performance, even by current standards, including its shock/vibration isolation to eliminate room rumble and incipient acoustic feedback distortion:
00:00 Intro
04:28 Sub-chassis' ground strap dissipates static charge (reduces pops/ticks)
04:57 Neutral balance tonearm (vs. typical stable balance) maintains a constant tracking force even on dips/warps.
08:54 Hefty platter + low friction bearing = speed regulation, but light enough to be driven by a highly accurate synchronous CLOCK motor
10:36 Neutral balance arm perk: tilted shelf friendly.
13:14 ULTRA low mass, acrylic headshell under 7g w/ wiring: low inertial mass where it matters most, to track difficult/imperfect records
14:13 Very rigid/inflexible "box-construction" headshell prevents microscopic flexing (distortion) despite its low mass. WARNING: delicate attachment threads! *
16:27 AR white paper "Skating Force: Mountain or Molehill?"- R. S. Oakley Jr., Audio magazine, Mar. 1967, p.40 summarized: It's unimportant, on this turntable/arm design, if using an adequate tracking force from the get go, however a DIY design like a weight suspended by a thread draped over a bent paper clip, attached to the arm, may be added if desired.
https://www.americanradiohistory.com/...
17:15 Dead accurate speed and very low wow & flutter, including actual stylus drag during the RPM test. [Even with my pulley's oxide and a cheap, aftermarket belt instead of AR's original belt, which were frozen solid and then machined on both sides for precise surface uniformity.]
19:51 Even "flat" LPs have micro warps (bumps/dips). AR keeps its pivot height MUCH lower than competitors so "warp wow" is reduced. I demo the XA pivot height to that of a $28K (TAS:$53,600?) tonearm using a 1 kHz test tone on the CBS STR-100 test record with an artificial warp.
28:15 Shock/vibration immunity hammer test No. 1.
32:07 Acoustic feedback "howl" immunity even @ MAX vol., mounted ON a full-range speaker + no "incipient acoustic feedback distortion", preventing the boominess/murkiness found with many competing designs, even at lower volumes
38:35 Ultra low mass headshell/arm: McProud Test success at 33 RPM. [WARNING: May damage the stylus on the competition!]
40:35 Full-size, NAB broadcast quality spindle diameter to minimize groove eccentricity wow.
42:07 Artificially induced, 1mm eccentricity wow audibility demo

THE FOLLOWING TEST MUST BE LISTENED TO WITH LARGE SPEAKERS WITH GOOD, DEEP BASS, IN A QUIET ROOM, OR FULL-SIZE HEADPHONES:

43:38 Floating sub-chassis to kill ROOM rumble, demo. Thanks to the VERY low resonance bounce (~4Hz) and inverted 3-pt. (like a tripod) spring isolation.

50:37 NAILING WOOD HAMMER TEST 2, literally ON the XA! It must be mounted on a dead solid surface. WARNING: Do not attempt.

THIS IS A 100% STOCK, UNMODIFIED MODEL!
[Other than replacing the organically decayed rubber belt, grommets, and platter mat.]

 The XA turntable and tonearm work together as an integral SYSTEM. [In theory one can mix and match but it opens a whole new can of worms for things that can potentially go wrong if the two designers had different goals or frames of reference for what is "proper".]

The low rpm clock motor minimizes vibration noise, decoupled from the platter via a rubber belt and has a constant, correct speed regardless of temperature or AC line voltage fluctuations.

 
"Despite being cheap, the AR turned out to be the single most important turntable of all time."

- HiFi News Magazine [the oldest audio magazine in the world and the largest in the UK] May 2009, p. 41
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Many top names in music owned this turntable, including Miles Davis:    • Miles Davis's audiophile turntable, t...  

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