The theory goes that around Stradivari’s time (a 100 or so years before) europe went through a mini ice-age, thus forcing the growth of the wood to be more compact, effectively tightening the annular rings of the wood during growth. Legend has it he used these particular trees when constructing his instruments, and as a guitar builder myself I can testify through a series of experiments that tighter-grained wood has a higher capacity of reflection of soundwaves (whereas looser grained woods have a higher propensity of absorbing vibration through air pockets) thereby increasing volume output and audible harmonic content.

His method of varnishing his instruments is also revolutionnary, using a thin and incredibly solid varnish that minimally impacted wood vibration capacity, the constitution of which I would be unable to specify here. Also his glues were most likely self-made using tendons and cartilage of animals, mostly rabbit and deer and other indigenous, rapid-moving animals. Tendon and cartilage have extremely high tensile strength with low density and superior flexibility, making them an ideal base for creation of a polyvalent, lightweight and durable adhesive substance.

His implementation of standard luthier techniques was spot on, and he even further developed techniques by experimenting and rigorously testing different internal and external bracing patterns (the bridge, in strict acoustic terms, is considered a brace.).

Hope this shines some light!

But the worst mistake this list made is bessler's, a well known hoax…. and especially strads violins, which were only particularily good because of the way the climate at the time affected the trees he used to make instruments from….. srsly, look it up and stop being lazy and sensational.