Belt driven turntables’ chief advantage over direct drive, idler wheel drive, and other drive systems is isolation from motor noise. The belt can be modeled as a classic mass-spring-damper system. Extensible, highly damped materials offer the greatest isolation from motor cogging and noise as these materials bring spring and damping properties to the drive system. As in any vibration isolation system, compliance and damping must be present for effective isolation. PERFECT UNIFORMITY OF THICKNESS The ultimate speed stability cannot be achieved without near perfection in the uniformity of thickness along the length of a drive belt. Limitations in casting techniques of rubber belts places a severe compromise in the speed stability in turntables using belts in the as-cast condition. To achieve more critical tolerances and greater precision a grinding process must be employed. Pertinent facts on grinding of rubber include the following: 1. The more desirable lower durometer materials are more difficult to grind. 2. As a compressible material exhibiting hysteresis effects, highly damped rubber compounds are more difficult to grind. 3. It is worth noting that round cross-section belts cannot be effectively ground. UNPRECEDENTED BELT PRECISION As research continued to confirm that a precision, flat, highly damped rubber belt is the optimal drive for a beltdrive turntable Basis Audio continued the search, over the past 5 years, for a company that could precision grind a rubber drive belt to 1/10,000 inch precision (.0001 inches/2.54 microns). Hundreds of requests for quotation were sent out, hundreds of follow-up telephone calls made, with each company expressing that we were asking for the impossible. In March, 2006 the decision was made to design in-house grinding equipment and develop belt grinding expertise. At various point in 2006 we experienced limited success, with usable belts first becoming a reality in November at a production yield of less than 25%. These belts were of standard thickness. As of February, 2007, normal thickness precision-ground belts (the Basis Revolution Belt) are shipping with all Basis turntables. The grinding operation is running at a 50% yield. We have achieved the desired 1/10,000” (2.54 micron) tolerance on a production basis.