I have been trying to figure out what mechanical/physical properties might be behind the terms used in the Yonex string guide. It would have been easier to figure out, if the material properties for the strings were available, but afaik they are not. The Yonex string guide from the Yonex website uses the terms 'Hard' as opposed to 'Soft' and 'Repulsion power' as opposed to 'Solid feel'. A similar Yonex string guide is shown at fx. BadmintonBay, not sure if this is created by Yonex. Here the terms are 'Hard feel' as opposed to 'Soft feel' and 'Quick repulsion' as opposed to 'Maximum hold'. 1) 'Hard' or 'Hard feel' as opposed to 'Soft' or 'Soft feel' I think it is likely that the terms 'Hard' and 'Soft' are directly related to the string's stiffness (unit N/m). Or more likely the dynamic stiffness for fast impacts, as from a speeding shuttle. Given the same string pre-tension, a stiffer string will feel harder as it will generate a higher maximum force during an impact. 2) 'Repulsion power' or 'Quick repulsion' as opposed to 'Solid feel' or 'Maximum hold' If I recall correctly, Yonex changed the term 'Repulsion' to 'Quick repulsion' for their string ratings at some point. Probably to clarify that it is about how quickly the shuttle leaves the stringbed after impact (short dwell-time), not about "power" as in the velocity of the shuttle after leaving the stringbed. What mechanical properties could be behind the term 'Quick repulsion'? As far as I can see, it is the dynamic stiffness again. The stiffer the stringbed, the shorter the dwell-time and the quicker the shuttle leaves the stringbed. The opposed term 'Maximum hold' which implies longer dwell-time backs this up. If this is true - that 'Quick repulsion' is (higher) dynamic stiffness - then a 'Quick repulsion' string would also be a 'Hard' string, but that is not what we see on the Yonex string charts. We see 'Hard' strings like the BG 80 with only medium 'Quick repulsion' and we see high value 'Quick repulsion' strings like the BG 66 UM rated to the 'Soft' side. So this puzzles me, hope some of you are be able to help.
