Suspended vs. non suspended turntable

Based on what I've been able to prove to my own satisfaction by tweaking a VPI belt-drive TT, I'm in agreement with Halcro regarding the merit of a non-suspended TT, but sited on a platform that provides a decoupling suspension.

An unsuspended TT with a standalone motor, combined with a belt made of non-compliant material such as thread or tape, should in most cases have superior speed stability relative to a suspended table with a soft rubber belt. The unsuspended design fixes the geometry between motor & platter. With a suspended TT, geometry & belt tension change constantly with variations in torque on the belt caused by modulation in stylus drag and plinth movement in the lateral plane-- resulting in variations in pitch.

Nonetheless, decoupling the TT from earth is still beneficial. If you can rap the rack with your knuckles and hear the sound through the speakers while the stylus rests in the record groove, then it's likely that the rack is acting as an antennae for LF vibration from earth or from AC transformers on the lower shelves or from acoustic waves from the speakers. Most of this energy can be absorbed in very low-frequency vibration by placing the entire suspensionless TT & motor assy on a decoupling platform of air springs or mechanical springs.

As an ancillary benefit it's easy to level up the TT by shifting the springs around.

Dan_ed, Admittedly, it is speculative to theorize concerning the impact of extreme LF seismic activity. However, though the effect of acoustic resonance & its harmonic content at frequencies above the fundamental LF tone is unpredictable, it is easy to observe anecdotally. A subwoofer or a stereo with good dynamics propagates strong vibrations at varying frequencies throughout the room: in the surface of racks, in the floors & window sashes, in the soft pillows of the couch, through one's foot, in the gut, etc. The TT platform, plinth and arm will all respond differently to this excitement. Tube microphonics is another common example. Whatever the merit of the knuckle-rap test, failure of this test evidences that the TT has not been isolated & suggests a probability that vibration at lesser amplitude is passing through the system. I'm panglossian enough to believe that it's better to pass than to fail this test. It’s not too much trouble to devise a decoupling platform that passes the test, and in so doing one may observe an audible improvement in focus and smoothness of HF. I doubt the improvement would be meaningfully confirmed in a frequency response test. An accelerometer on the TT would probably better indicate what’s happening.

I would posit that a sprung suspension is the best way to reliably dissipate vibration into benign LF mechanical energy. The mechanics of other more complex approaches involving constrained-layer damping are more complicated to execute reliably and with repeatable results in combination with the wide variety of rooms, platforms, racks & floor compositions in general use.

As one moves up the food chain to very expensive TTs (e.g. Rockport, Caliburn, Grand Prix), an integral platform and/or rack design becomes a holistic design element. My sense is that most standalone TTs are compromised partly by cost & partly in order to optimize performance independent of siting issues. With belt-drive TTs, there might also be trade-offs between the sometimes competing design goals of transient speed stability & resonance control. As remarked by one TT pro in these forums, even small amounts of compliance in a TT suspension (such as rubber footers under a motor) sacrifice speed stability by creating an unstable geometry between motor & platter.

A suspensionless TT on top of a decoupling platform is at least one way to separate variables that affect speed stability and resonance control, and to reconcile these two design goals. I was myself skeptical of the approach, but positive feedback from owners of unsprung tables like Raven and Scout TTs (who counter-intuitively found benefits even in combination with wall racks and concrete floors) confirmed my own results with a modded unsuspended VPI TNT. If one accepts that TT and platform/rack are a system, it’s not much of a stretch to justify tweaking individual design elements in each as to logically complement each other. The question of whether this transgresses the immaculate conception of an original designer is a matter for religion.

The springs I'm using are rated 40-60lb. each & six springs are used to support a 100lb TT plus a 200lb. sandbox.