How many hours are required to fully ‘burn’ in a pair of new speakers?
It depends on the speakers. Some take a long time while others take a shorter time. My view is that speakers with metal components like metal tweeters (aluminium, titanium, beryllium) or woofer cones (aluminium, magnesium alloys, etc) take a longer time to burn in.
Allow me to SKL here! In my experience metal/kevlar type drivers that are typically made from stiff materials tend to need longer break in time compared to the usual paper/poly material cone which are softer. There are no hard & fast rules about speaker or cable, or just about any hifi equipment break in.
Just watch out for the following symptoms, if the equipment sound shrill, or even ear piercing sometimes on the high frequencies, it’s not broken in yet. Speakers in particular are very guilty of this trait, when properly positioned in a given room, sound should not be beaming from the left and right speakers. Well run in speakers should sound out of the box, rather than sticking around the box. Although sometimes, an under powered amplifier used to drive a pair of given speakers could result in the same effect too!
Use your hearing experience is best, even if most equipment manufacturers say 200-500 hours to burn in is sufficient.
Specifically I am referring to the KEF LS50. I have read that some speakers may even take a few hundred hours. It seems 200 hours is the minimum at least for a new pair.