FWIW we weren’t actually trying to make a better sounding belt when we started developing the blue belts. The original intention was just to make really high quality well fitting belts belts at a good price. The advantages in sound quality however quickly became apparent and came as a surprise bonus.
All too often the belts people are using do not fit optimally and this can have all sorts of repercussions for bearing wear/noise, premature belt wear and increased wow and flutter.
A correctly fitting high quality belt can bring a very surprising uplift in sound quality. On my own Thorens TD125 for example I was measuring about 0.24% wow when using a new genuine Thorens butyl rubber belt and this dropped to 0.06% when switching to the first version of the Bluebelt. I've since got this down to about 0.02% after some further refinement of the belt spec. Quite an improvement I'll think you'll agree and clearly audible. And all from just changing the belt.
The Thorens TD124 is another case in point. The motor capstan is reversible with two sides. For use in areas with 60Hz main electricity you use the smaller diameter end and for 50Hz operation you use the end with the larger diameter. It’s obvious that the optimum belt length is going to be longer for the 50Hz setting that for the 60Hz setting and yet Thorens themselves only supply one belt which is supposedly universal for both frequencies, which is madness! In practice the genuine Thorens belt is just a compromise size and is actually a much better fit when used on the 60Hz setting. It is far too tight at 50Hz. The situation is compounded by third party manufacturers whose belts all over the place in spec and are usually are even tighter.
The standard way of making belts is to make a closed loop from a open ended ribbon of material. On a quality belt the glued end end is then ground flat to remove any imperfections at the glued join, hence you'll often see descriptions like 'precision ground' applied to these belts. Better still, Bluebelts belts are manufactured as a single continuous circular piece and can accurately be described as 'endless' belts.
Most turntable belts on the market are made from black butyl rubber but Nanocamp blue belts are made from silicone rubber, which is an inherently far superior material for making turntable belts from. Butyl rubber really can be considered an obsolete and defunct material now and should be relegated to the past.
So even without any sound quality differences I consider the Bluebelts to be a generally better quality belt than generic belts on the market.
But sound quality improvements are very consistently reported by our customers when switching to the Bluebelt even in situations in which no there is no measured improvement in wow and flutter. I hear it myself on my TD125. So something else is going on...
A major contender as an explanation is the consideration of motor cogging torque:
From wikipedia: Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a permanent magnet machine. It is also known as detent or no-current torque. This torque is position dependent and its periodicity per revolution depends on the number of magnetic poles and the number of teeth on the stator. Cogging torque is an undesirable component for the operation of such a motor. It is especially prominent at lower speeds, with the symptom of jerkiness. Cogging torque results in torque as well as speed ripple; however, at high speed the motor moment of inertia filters out the effect of cogging torque.
And it's not just cogging either, the motor is a source of other mechanical noise too, some from the motors bearings and other vibrations caused by the imperfect dynamic imbalances of the motor assembly.
Now imagine two alternative belts on a belt drive deck. One is very pliable and elastic and the other is much stiffer and not very stretchy. It's quite easy to imagine that the softer more elastic belt might be better at decoupling the motor noise from the platter and also be better a smoothing out any motor cogging torque pulses.
Another factor which needs to be considered is the resonant frequency of the belt, which is largely determined by the unsupported length of the belt between the pulleys (trum length) but also by the weight of the platter, belt tension and transmission ratio etc. Again it's easy to imagine how a belt with a different resonant frequency may possibly affect the sound as it will be transmitting a vibration to the platter of a different frequency.
FWIW I do consider the Linn belt to be a well engineered product although the price Linn charge is a bit of a joke. There's also no doubt that it works brilliantly with the tapered pulley/capstan design used on the LP12 motor and that's not something that can always be said for our belts, which in fairness don't always get along well with this design of capstan (not an issue with majority of turntables). To that end, I don't consider our LP12 spec belt to be a perfected product in the way that I do consider the TD124 and TD125 belts to be.
