More and more “tennis-stringers” start to string on stiffness, and string-bed-testers are used in tennis for more than 20 years. Stringing on stiffness means that you aim at a certain stiffness-result in the racquet, advantages of this system are: * The player feels the stiffness in the racquet and not the tension that is used on a stringing machine, so the stiffness is a better reference for the playability of a string bed. * The stiffness in the racquet can be measured after stringing and after play, which makes it possible to check the result and loss of tension after play. * Stringing on stiffness is more accurate because there are a number of “inaccuracies” between the tension on the stringing machine and the final result in the racquet like: - Slipping clamps - Fast stringers which are ‘soft' stringers. - The difference between stretch qualities of strings. - Tension units with good or with bad constant pull action. These inaccuracies cause big differences in result between different stringers with their different machines. * If a stringer uses a string bed tester he can check the quality of his machine, himself and of the string he is using. The stiffness is measured in kg/cm, 20 kg/cm means that 20 kg is needed to deflect the stringbed 1 centimeter. I am interested to hear opinions about this item. Stringtechno
more accurately, we should be stringing on response instead of stiffness. stiffness is static, meaning you are hanging a static weight on the string. while response is dynamic, it is basically the inverse of the natural frequency of the stringbed. i (and some others) have been measuring stringbed frequencies for matching for a while now. and others have been doing it too. but without awaring it. many have suggested using lower tension for cab frames, because cab tend to have a smaller head thus producing a faster response. many also have suggested lower tension for thinner strings, same reason.
If any of you have ever used a Babolat RDC (or similar) before, there's a test whereby a plunger moves into the stringbed to deform it and measure the force/deflection ratio. The units are arbitrary - it's a 0-100 scale - but the principle is, I think, what the OP was referring to.
I think that there are some misunderstandings: I never heard about the term “response” in connection with the deflection of the string bed on impact of the ball or the shuttle. But it is certain that there is a direct connection between the natural frequency of the string bed and the stiffness. f = 1/ 6,28 * root C/m In which f is the fequency, C is the stiffness and m is the mass with or without the mass of the stiffness tester. As you may know the principle of the stiffness testers ERT300 and Stringway Stringlab is based on the measuring the natural frequency and from that they calculate the stiffness with the formula above. It is certain that stringing tensions went down considerably in Tennis since the introduction of these stiffness testers. I think that tensions will go down in badminton also for 2 reasons: 1. In a “2-spring model” like a racquet the weaker spring will deflect more as the other spring gets stiffer. I.o.w; When the stiffness of the string bed gets much higher than the shaft of the racquet , only the shaft will deflect and the shaft will determine the playability of the racquet. The player will not feel the difference between a string bed stiffness which is 2 times higher than the shaft or 2,5 times higher. (Are there any values for the stiffness of modern frames?) 2. When the string bed is very stiff it will not deflect and the string will not stretch. This means that the player does not feel the elongation qualities of strings any more. Is this the intention of those high tensions in badminton? All strings will feel the same. Resuming: * The stiffness of a string bed decides what the player feels of his string and shaft. In tennis the stiffness can make and brake the playability of the string bed; * There is no use in using high quality (concerning the elasticity) strings at high tensions because the player does not feel these qualities anyway. * The ERT300 and the Stringlab can not be used for badminton because the shaft is too weak in relation to the stiffness of the string bed. The tools cannot distinguish the vibration of the string bed from that of the shaft. * A static stiffness tester is better for use with badminton racquets, provided that the racquet head will not bend during the stiffness test.
your formula might be been pre-simplified. there are 3 factors to the frequency: 1. density 2. tension 3. length your formula, as i said, might have taken into account a certain racket head size as well as certain material used. that maybe true for some rackets, but not universally true. badminton rackets comes in many varying sizes and shapes. here is the reference from wikipedia, it references a single string, a string bed of varying size will have similar factors: Frequency of the wave Once the speed of propagation is known, the frequency of the sound produced by the string can be calculated. The speed of propagation of a wave is equal to the wavelength λ divided by the period τ, or multiplied by the frequency f : If the length of the string is L, the fundamental harmonic is the one produced by the vibration whose nodes are the two ends of the string, soL is half of the wavelength of the fundamental harmonic. Hence: where T is the tension, μ is the linear density, and L is the length of the vibrating part of the string. Therefore: the shorter the string, the higher the frequency of the fundamental the higher the tension, the higher the frequency of the fundamental the lighter the string, the higher the frequency of the fundamental Moreover, if we take the nth harmonic as having a wavelength given by λ[SUB]n[/SUB] = 2L / n, then we easily get an expression for the frequency of the nth harmonic: And for a string under a tension T with density μ, then
stringtechno: re your post above, you have to realize that there is a very fundamental difference between tennis and badminton re tension choice. In both sports, it is a given that advanced and pro players are not looking for more power, but for more control. ...... In tennis, string tensions are already quite high 50-60 lbs, and better control is achieved thru lower tensions, as the ball needs a certain amount of time to be compressed on the stringbed for the racket to impart direction. ..... However in badminton, we're stringing around 24-32 lbs. And better control is achieved not by lower tensions, but by higher tensions, because lower tension would allow the stringbed to move too much and become unpredictable in controlling direction. ..... Paradoxical but true.
We are talking about different vibrations: I mean the natural frequency of the hole string bed, which depends on the stiffness of the total string bed. When a stiffness tester like the Stringlab or the ERT300 is used to measure the stiffness of a string bed, the mass of these tools vibrate on the stiffness of the string bed. Because the mass is known the tool can calculate the stiffness of the hole string bed from the measured natural frequency. You mean the natural frequency of one string which is tensioned in the racquet. This is useful but tells nothing about the final stiffness result of the hole string bed. I do not think that there is a difference between tennis and badminton concerning the control of a string bed. In both cases counts the bigger the `spring back effect´ of the string bed the bigger the power that is generated. That is why hard hitting tennis players prefer higher stiffness and top players with more feeling can play with lower stiffness and can use the generated power of the string bed in their advantage. Federer and Nadal both play with low stiffness from 32 to 35 Kg/cm. In my opinion there is a better way of offering control then raising the tension more and more. Offer the player a string with less elastic elongation.
Hi guys, I would like to understand why such a fundamental discussion “ drops dead” while it is really the basis of understanding better what stringers actually create in the racquet. And how the stiffness of the frame and the string bed should be tuned in relation to each other. It does really not make any sense of stringing on a very high stiffness while the shaft is much less stiff. This picture shows the actual system, all the deformation will go into the lower stiffness. Iow, the player will not feel the difference between 12 and 15 kg at all. Could a lot of this very high tension wish not be " between the ears" of players???
