Holbo Airbearing Turntable Lab Report

Lab Report

Measured directly through its Teflon spindle and bearing sleeve, rumble is a moderate –68.5dB (DIN-B wtd, re. 1kHz/5cm/sec) with a cluster of low-level modes between 75-85Hz making an appearance as the principal resonances. Gratifyingly, this figure improves to a low –71.8dB (through groove) thanks to the isolation afforded by the weighty POM/Delrin platter, and all without the services of an aftermarket clamp. The platter gets up to speed in a relatively swift 3-4secs but, as supplied, our sample was running a full +5% fast – fortunately the rear trim pot adjustment has sufficient range to accommodate at least ±10% either side of 33.33rpm. Absolute speed now achieved (before shipping to Ken) the drawback of many DC motor-equipped decks was subsequently revealed by the low-rate drift visible on the W&F spectrum [see Graph 1, below]. Many listeners are evidently insensitive to these 0.5Hz-1.5Hz changes in speed so the Graph, and 0.15% peak wow, 'look' worse than may be experienced in practice.

The 163mm alloy tonearm tube is damped with an internal foam that holds the silver-plated copper litz wiring in place and successfully quells the harmonics and twisting modes following the main 150Hz bending resonance [Graph 2]. The cartridge mounting platform adds little to the overall 7.5g effective mass, so it remains best suited to higher compliance MMs than low compliance MCs. Friction is low enough at ~30mg within the 'air bearing'. In this case air is forced from within the sleeve rather than perforations in the supporting barrel, so while lower friction might be obtained by a higher air pressure, noise at the arm would increase. Holbo has achieved a fine compromise here. PM


Wow and flutter re. 3150Hz tone at 5cm/sec (plotted ±150Hz, 5Hz per minor division)


Cumulative tonearm resonant decay spectrum, illustrating various bearing, pillar and 'tube' vibration modes spanning 100Hz-10kHz over 40msec

Turntable speed error at 33.33rpm 33.35rpm (+0.05%, adjusted)
Time to audible stabilisation 4sec
Peak Wow/Flutter (Peak wtd) 0.15% / 0.04%
Rumble (silent groove, DIN B wtd) –71.8dB
Rumble (through bearing, DIN B wtd) –68.5dB
Hum & Noise (unwtd, rel. to 5cm/sec) –58.7dB
Power Consumption 4W motor / 6W pump
Dimensions (WHD) / Weight 430x150x420mm / 12kg
Price £6500

Holbo S.P.
Ljubljana, Slovenia
Supplied by: Hi-Fi Traders Ltd, Guestling, UK
020 3714 7236