# Stringbed frequency to monitor string tension

Discussion in 'Badminton String' started by visor, Feb 27, 2013.

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there are theories. but actual measurements?

it is hard to do.

1. where to find a environment where we can achieve such temperature variation? we need some sort of temperature controllable oven / fridge.

2. how to do the experiment so it is fair? hard to describe but let me describe this scenario. if i string a racket at 25lbs at 30C. i move it to 0C. we know that will increase the tension. and then afterwards, we move it back to 30C. will it still be at 25lbs? the increase in tension will more effectively stretch the string and modify it's property. so how is it possible to make such measurement? do we start cold? start hot? start somewhere in the middle?

#41

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imho, temperature is a orthogonal variable to this experiment / data gathering. as long as we keep the temperature relatively close, ie. the racket is strung in Canada and used in Canada, strung in Singapore and used in Singapore. then it will be good enough.

the temperature experiment can be done independent of this experiment and will take a lot more thoughts to plan it in such a way to make it reliable and accurate.

#42
3. ### Licin Regular Member

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Yes agreed. we must indicate the countries when we post the data. So that members who are living in a country with the same weather condition should be able to use that data as a reference.

#43
4. ### visor Regular Member

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Just did a simple test re temp vs freq... racket (RKEP XP70 with zm62 at 22x23lbs) was placed indoor and outdoor for at least 2 hours before measuring.

1077 Hz at 20C
1075 Hz at 5C
1077 Hz at 20C again

Does that make sense? So there is no difference, and even so, the freq dropped with lower temp, meaning that the string loosened instead of contracting? Huh? I would have expected the freq to rise with lower temp due to string contraction...

In any case, if there's not much significant freq difference with a 15C drop, then can we safely assume there won't be much difference going in the other direction, with a 15C rise? Anyone in Malaysia/Singapore want to measure that?

Hmmm... I should also test vs850 tomorrow night.

#44
Last edited: Mar 4, 2013
5. ### cobalt Moderator

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The string probably didn't loosen as much as the metal on the frame would have contracted...

A lot of places in Malaysia/Singapore/Indonesia etc etc do away with air conditioning (or limited a/c) so the temperature is probably consitently above 25C... prolly 30C in some places. Now, if a racquet was strung at say 26/28 and remained at the same temperature for a couple of days, would it return a significantly different frequency to one (same racquet preferably) strung at 26/28 in say, Edmonton in winter?

#45
6. ### visor Regular Member

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Last time I checked my racket frame is not made of metal. Perhaps you're still using an old Yonex B500.

But in any case, the frame whether metal or graphite is a closed loop of an oval... there's no room for it to expand or contract. In other words, the surface area remains the same, whether it's hot or cold, whether it's under 36 lb tension or 0 lb tension.

Now your second part is where I want people with accurate tensions to provide their frequency readings from all over the world, at different temperatures. My guess is within 15-35C, there's not much difference...

#46
Last edited: Mar 4, 2013
7. ### cobalt Moderator

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Nanomeasure would leave nothing to chance! Who are you, imposter???!!! What have you done with Nanomeasure!!!

#47
8. ### visor Regular Member

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#48

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i have to disagree. the head will expand and contract under heat/cold and result in a bigger/smaller oval.

#49

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the temperature experiment is interesting and reveals something that we didn't take into account and that's the expansion and contraction of the frame due to temperature. if the rate of expansion and contraction of the frame is similar to the string, then there is nothing to worry about. however, it looks like the rate of contraction is actually higher on the frame resulting in a almost negligible change in the observed frequency.

#50
11. ### alispecs New Member

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There is a lot of good info and insight here. I also notice the relationship between the frequency droppage vs time elapsed after stringing. It seems to me that there is few consensus among our observations.

1. Frequency loss is the greatest during the 1 week. It will stabilize after 1 week if unused.
2. Frequency loss will further deepen with use even after 1 week.
3. Factors such as strings, stringers, temperature, humidity may play a role in affecting frequency loss but it is hard to quantify at the post with our scale or set up.

If the object of this exercise is to fine the best tension for our string, one can ignore all other factors and just focus on the frequency. It is best to test your new tension after 1 week when it is stabilized and test it again after use. Or, use the Carltune the measure the frequency of the racquet at the session that you feel you have the best tension. Use the frequency to determine the tension you need to achieve and the time you need to wait for it to achieve that frequency.

For example, for your racquet and string, you best frequency is 1000 Hz. The string will achieve that 1000 Hz at 24lbs after 1 week OR at 26 lbs after 1 week and 1 or 2 session of play. Then we should only judge our play with the same frequency every time to find any subtle differences with other changes in our game (etc, changing to a different string).

This may explain the psychological feelings that new string is better only the 1 week and it degrades after 1 or 2 sessions. Just measure the frequency to confirm.

Use the frequency as a guide can give us an objective measurement and tell us if the 2 racquets are identical in tension even if they are stringed by different stringers, machine, etc. (ie. if they have the same frequency)

By keeping the one factor constant (frequency/tension) stable, it enables us to perform a better judgment if we are going to alter any other part (ie. racquet, string type) in our equipment.

I won't be surprised if Yonex engineers also possessed a complete data for all the strings.

Hope this helps.

#51
12. ### visor Regular Member

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You're correct.

Coefficient of linear thermal expansion of pure graphite is 4.4 x 10^-6 in/in°F, and for aluminum is 12.3.

So for 15C change is 27F change. Plug in 27 in for frame circumference.
Results in 0.0032 in, or 0.081 mm.
Somehow that is very negligible.

#52

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hehe. so there IS!!

i agree though, it is negligible.

but how do we explain your observation then?

#53
14. ### cobalt Moderator

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Have you tried it? Did you measure it with your electron microscope? Did you leave your favourite racquet out on the cold, cold mountain for a day, then slow-roasted it over the barbeque, and measured the difference?

If everything in the real world could be explained through physics and theorems and stuff, we would all be visor than we are...

#54
15. ### visor Regular Member

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Lol! Lemme check the coefficient for cobalt and see if I need to subject it to extreme temps...

#55
16. ### visor Regular Member

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I don't know... I'll check vs850 tonite.

#56

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2 rackets. NS9000, AT900P

both strung with NBG98 @ 23.8/26lbs

0hr:

NS: 1212.3Hz
AT: 1193.4Hz

3 hrs:

NS: 1188.4Hz
AT: 1162.1Hz

17hrs:

NS: 1177.0Hz
AT: 1150.4Hz

#57
18. ### visor Regular Member

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VS850 at 24 lb on SW30 from 9 months ago, rarely played

1027 Hz at 20C
1023 Hz at 5C
1027 Hz at 20C again

So, there is a trend. Tensions fall off a tad when colder. But this is only like 0.1 lb and the string material hardening with colder temp is probably more significant in causing a harder brittle feel in the cold.

Still would be interesting to see what happens in Asia going from 20C to 35C. Anyone?

#58
19. ### ucantseeme Regular Member

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Today, at 1123 Hz. String and tension feel comfortable, powerful and are superb IMO.

#59
20. ### blableblibloblu Regular Member

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Looking at a few frequencies provided and comparing, it seems to me like Victor racquets tend to have a lower frequency at the same tension as lets say Yonex. Could have to do with the fact that they don't fill the racquets with foam.

#60