So according to this adding lead at 10 & 2 would provide very little vibe damping since it's right at the node? I've always preferred weight at 10 & 2 as it seems to change the way the racquet behaves the least, maybe this is why. But it certainly seems to absorb some shock and make the frame feel more solid and comfy. In my exp, adding lead at 3 & 9 seems to add the most comfort (seems to absorb the impact the most), and 12 the least, which would go against this. Are impact shock and vibration two separate factors?
Hello Again Keith
I apologize in advance for the lengthy reply. Lots of overlapping factors, and numerous scenarios at play. Regarding shock and vibration, there are a few different flavors, and it mostly depends on where the ball is striking the string bed.
1. Impact shock: Is the very first initial jolt of the vibration wave pattern, and is strongest when you miss the sweet spot high. It's that first initial dull "thud" you feel most noticeably when you strike near the tip of the frame on a flat first serve. We all know what that feels like, and it's not pleasant. What is happening is the handle is being jerked forward in your hand violently, (as the racquet rotates around the center of mass in the throat) and your arm goes right along with it. The vibrations are what comes after that, and vibration occurs well after the ball has left the string bed. See my 2nd photoshop image below. Much more detailed explaination in the links below.
2. Impacts in the sweet spots (COP+Node) : These two points are only a few centimeters apart, if you hit one you are probably hitting the other as well. There are some very fine differences btw the two sweet spots, but what it boils down to is that both shock and vibration are minimized when you hit center. The frame flexes a little bit, snaps back, but does not overshoot the center point, and finds equilibrium as a straight beam. Thats why you feel little or no vibration when hit on center. It's also why flexible frames are just as powerful as stiff frames when you hit the sweet spot (Yes I said that!). The racquet isn't vibrating very much in either case, so there isn't much kinetic impact energy being lost to frame vibration. Both impacts are pretty efficient. For more on flexible frames, stiff frames and racquet power see link #119 in the thread below.
http://tt.tennis-warehouse.com/showthread.php?t=455102&highlight=flexible&page=6
3. Impacts off center low : You get the vibration in the uniform beam pattern, but now the frame is translating more (pushed straight back), and rotating less. There is impact shock and vibration here as well, but is a bit more muted than the sensation you experience when you miss high.
4. Flexible frames travel a greater distance when they flex. This increases dwell time, and makes for a "softer landing" so to speak, when the ball strikes the string bed. Stiffer frames bend less on impact, dwell time is shorter, so this increases impact shock. Stiffer frames bend less, and the vibrations are happening much quicker. That's why the EXO Tour 100 18x20 has a vibration frequency of 123 cycles per second, and the 2012 PDR+ has a vibration frequency of 164 Hz. Given that spread, what we are talking about with customization is akin to fine tuning, rather than transformation.
http://twu.tennis-warehouse.com/cgi-bin/vibfrequency.cgi
http://twu.tennis-warehouse.com/learning_center/vibration_explanation.php
http://www.physics.usyd.edu.au/~cross/tennis.html
5. On Adding mass and increasing flex and Dwell time: A recent study (see link below, and props to corners for bringing this to light first) has indicated that adding 30 grams of lead to the tip of a frame will drop the vibration frequency by 12 hz. While that can probably be felt, adding 30 grams to the tip is not typical and adds quite a bit of SW. If you assume (and that's a big assumption) that mass at the butt will be just as effective at lowering vibration frequency, as it is at the business end of the stick, that could make a noticeable "fine tuning" kind of a difference, but not a "transformational" type of difference in my estimation at least. Just to get a feel for the frame of reference here: A 2012 PD has a vibe frequency of 170. Exo Tour 100 is 123. Volk C-10 is 137. IG Prestige MP is 150. Another good reality check is simply looking at the PD vs the PDR. They are essentially the same frame, but one is heavier. The 2012 PD is sw 318 and 170hz, the PDR is sw 328 and 163 Hz. So in this case, with this frame, ten more SW units = drop in 7hz.
http://www.physics.usyd.edu.au/~cross/PUBLICATIONS/16. Customising.PDF
6. Adding lead at the tip does nothing for stability on off center hits out toward the edges at 3-9, but adding mass at 3-9 does. That added stability is felt as a wider sweet spot, which is why mass out there feels more comfy. When you miss high, the impact shock will you always let know it, and you are likely to chalk it up to operator error. When you miss out towards 3-9 you dont always know it, but you feel the very real effect of an expanded sweetspot with mass there.
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-Jack
