This make sense?

norcal

Legend
2 identical rackets (Ezone Xi), strung with same string, same tension, same machine. Despite using a DW with floating clamps my string jobs are very consistent (usually within .3 of lb).

Been hanging on to a new Xi for a couple years, it has only been strung 3 times now. the 2nd Xi had been in the rotation for years, been strung probably two dozen times.

The new Xi is coming off the stringer 2.3-2.5 lbs tighter than the old one. First thought it was a fluke but a second stringing of each got the same exact results.

Is this to be expected because of the 'newness' (although it is chronologically old) of the frame, grommets etc? I realize rackets get flexier with use/stringjobs but I didn't realize it translated to tension.

/yes I'm bored
 

AndI

Rookie
Can you please comment on how you determine the tension of the strung racquet? Is this measurement based on resonance frequency of the string bed? If this is what you use, one should not forget that the resonance is determined by a combination of strings and frame, as vibration comes from the whole thing. My best guess is that something in these two frames is not identical, and this "something" makes them vibrate at slightly different frequency. Perhaps stiffness of the frame material has changed over time from playing. You know, like your slalom skis get softer after years of use or skiing bumps, so can change the racquet frame. This, however, does not necessarily mean that the string tension is different. Change of frequency means that the combination of the string bed and the frame is a little softer on your older racquet.

This is an interesting observation. Thanks for sharing.
 

esgee48

G.O.A.T.
Have you checked the length of the frames? If one is slightly shorter, that means the crosses are 'not quite' at ref tension.

I use Racquet Tune. The only time I notice there is a difference is when new grommets are installed. I replace them all the time for clients. When I ping their old racquets/old grommets, I will come close to ref tension ±0.2# max. My records indicate that pinging old racquet/new grommets result in almost a lb less tension, probably due to unsettled grommets.

When I do completely new frames, they exhibit the same behavior by pinging out lower. To compensate, I add 1.5# to ref tension, then go back to normal on subsequent string jobs.

What you described is not what I have experienced. I do know that hoops deform differently based on racquet useage. I try to compensate for this by making sure that the frames' length are the same before and after. If a used frame come in and it is not 27" long when it should be, I will 'pre stretch' the frame to try to get it back to normal. I will also take extra care with the crosses to make sure that I have ref tension along the entire length. Doing this, I have recovered as much as 3-4 mm of length back from short frames.
 

Irvin

Talk Tennis Guru
Only explanation I can think of is the grommets is the frames that have been strung 24x are smoother on the inside and the friction is lower. You may want to try replacing the grommets in all rackets to set if the tensions even out.
 

Rabbit

G.O.A.T.
@esgee48 - yeah, on new frames, the practice/rumor/wive's tale was you needed to bump tension to "set" the grommets. I suspect what @norcal is seeing is a difference in new v old grommets.
 

Irvin

Talk Tennis Guru
A two year old racket that has been strung three times is not like a frame with new grommets.

Been hanging on to a new Xi for a couple years, it has only been strung 3 times now. the 2nd Xi had been in the rotation for years, been strung probably two dozen times.
 

norcal

Legend
These measurements were from racket tune. Didn't know the frame could affect frequency but that makes some sense.

Thanks for the input, I will check the length of the racket as well as check it with a gamma string meter. As for grommets I actually was not accurate when I said the new racket had been sitting around for a few years...it's a 2013 model I believe so that would be 6+ years (I bought it new from a tennis shop on the bay a couple years ago).
 

brownbearfalling

Hall of Fame
Wild guess: maybe the flexing of the racquet hoop (softer older frame and stiffer= newer frame) causes the difference in the tension. Even then I would think the difference would not be that significant.

I’m curious. Do you notice the difference in the way they play?
 

AndI

Rookie
These measurements were from racket tune. Didn't know the frame could affect frequency but that makes some sense.
Well, this makes sense to me, too. Racquet Tune (as well as ERT-300 tennis computer) uses the physical model of standing waves in a fixed-fixed string as the first approximation. If you would use two rigid clamps spaced at a distance L from each other and clamped a piece of string with density P tensioned to the tension T, then its primary resonance frequency would be

F = (1/2*L) * SQRT (T/P)

Density P is the mass of the piece of clamped string divided by its length. These are input parameters into racquet tune.

When string vibrates, it deviates from a straight line, stretches a little, and exerts additional force on the clamps. If the clamps are not rigid, e.g., when a somewhat flexible frame serves as "clamps", then the frame starts vibrating as well, and it has its own resonance frequency which is probably fairly low, on a relative scale. This will create additional harmonics in vibrations of the whole thing, and this could conceivably shift the readings picked up by racquet tune.

Of course when you measure the complete string bed, you measure a very complex oscillation of multiple strings of different lengths and the frame, interconnected into the string bed. I looked at Fourier transform of the sound of the string bed after impact, picked up by a decent quality (about $150 - $200) studio microphone, and it is a freaking mess. Peak after peak after peak, all relatively small, like 5 to 10 dB or less. It is not like a piano or a guitar sound where you see the main note followed by harmonics.

A thought that you can measure tension with a racquet tune is a little bit of a stretch. There definitely is a correlation, but it is more complex than just tension vs frequency, and I am sure the frame (and grommets, for that matter) have an impact. When racquet tune gives you a shifted reading, it does not necessarily mean that your tension is different. It means that the resonance frequency, or whatever racquet tune is able to pick up as the resonance frequency, is different. You can theoretically have different resonance frequency of the string bed on a frame for exactly the same tension. I think you actually do have the same tension, regardless of what racquet tune tells you. But your string bed resonanates at a lower frequency for some reason, and usually this is percieved as a softer string bed. But you know, if you have a softer frame, its string bed, everything else being equal, would also be percieved as a softer one than with a stiff frame, for exact same strings and tension.

Since you are on it, a simple experiment could be to take a measurement with racquet tune on a free-standing racquet and on a racquet on the stringing machine. Grippers of the stringing machine would suppress some of the vibrations of the frame (6 points is much better than 4 and WAY better than 2 for the purpose of this test). I am curious what difference in reading you would see. I suspect, there may be some. I tried the same thing without measuring anything, and I could clearly hear the difference in sound.
 
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norcal

Legend
That's a lot of interesting info Andl. I will try that next time I string them up.

The rackets are the same length (or within 1/16th of an inch).

They do play similar tension wise. The older one does feel more 'flexy' in play (and has a stress crack in the throat).

Thanks for all the input!
 
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