# Thread: Stringbed frequency to monitor string tension

1. ## Stringbed frequency to monitor string tension

(Updated and summarized Nov 2015. Original post quoted below the update.)

Have you ever wondered if there is a way to determine whether your newly strung racket is at the right tension that you asked for? Perhaps you're trying out a different stringer, or you're stringing yourself and you're not sure whether the string job is consistent. Or perhaps you're wondering why after playing a few weeks your strings don't feel as crisp as it did initially, and you just want to monitor the inevitable tension drop so that you'll know to string a bit higher next time. Or whether the 30 lb that your friend says he plays with is really that when it feels less tight than the 25 lb that you play with. Or perhaps you just want to monitor more precisely and objectively your preferred tension than just by pushing the stringbed with your fingers or pinging the strings to the ear.

Fortunately with the ubiquitous existence of smartphones, there is an easy way to achieve this by using a smartphone app to measure the fundamental or dominant frequency of the stringbed.

For tennis, an app exists that measures the frequency, and given information on string diameter and racket face area, it will calculate the string tension. This however doesn't work as well for the lower tensions used in badminton.

For badminton, there are several tuner apps for smartphones that can be used to measure stringbed frequency, eg. CarlTune for Android, and ClearTune for iOS. It's quite easy; just flick or strum lightly across the stringbed with your 3rd and 4th fingers like a guitar, and let it ring close to the mic on your smartphone preferably in a quiet room. As in this video.

https://youtu.be/ahW2gZbVg4I

The dominant frequency reading should be in the range of 1000-1300 Hz for most strings strung in the usual range of 20-30 lbs, where each 1 lb change in tension results in about 30 Hz change in frequency. Obviously the frequency will be in the higher range with higher tension, thinner string (eg. ZM62, BG66UM), or smaller racket frame (eg. Jetspeed 10, ZForce ll) in accordance to

(See reference #1.)

I had initially started a thread to pool data points for various strings at different tensions here (http://www.badmintoncentral.com/foru...string-tension). Kwun and other stringers had kindly contributed tables and tables of data points and soon we could see the difference between thick and thin strings. Interestingly, Kwun's measurement of a single piece of ZM62 string under various tensions correlated directly to my measurements of a ZM62 stringbed after a few weeks of play.

Soon after, discussions naturally turned to whether measurements should be done immediately after stringing or after being played. Due to irreversible stretching at the molecular level within the string material itself in the first 24 hrs after it comes off the stringing machine, there's about a 30-60 Hz (corresponding to a 1-2 lb) loss, and that's before even any shuttle is hit. And then there's a more gradual drop of another 30-60 Hz (again reflecting another 1-2 lb) loss after a few sessions of play. (This however is not as serious as in the tennis world where a typical 60 lb job will lose 5-10 lbs in the first 24 hrs before any balls are hit and another 10-15 lbs after the first 100 hits!)

Higher initial tensions will lose more, and certain strings (eg. BG65, VS850) that are well known for their tension loss will also lose more if not properly prestretched.

Other factors that mitigate tension loss include mostly stringing techniques such as ECP (electronic constant pull) machines, slower and longer pulls, sturdy clamps and side supports, 2 knots 1 piece stringing (possibly) vs 4 knots 2 pieces, special finishing knots etc.

Accepting these sources of tension loss then, the real tension that we play with is dependent on the time it has been since strung and the time it has been played with. So a requested 27 lb job will drop to an actual 25-26 lbs 1 day after stringing without play and then continue dropping to 23-24 lbs after 10-20 hrs of play. Maybe that's why pro players need to restring their rackets every week! In any case, the most important thing is that we all like to play with a certain consistent tension, hence this objective method of monitoring string tension.

References:

#1) How string frequency is related to tension, string length and density.
https://en.wikipedia.org/wiki/Vibrat...cy_of_the_wave

#2) Changes In String Tension Affect Racket Performance (http://www.ashawayusa.com/BadmintonTip2.php)

#3) Post by Lieu201 on treating the stringbed as an elliptical membrane to directly calculate the frequency

As some of you may know, I'm pretty meticulous in measuring my equipment... (now get your mind out of the gutter)... I'm referring to my rackets.

I also like to keep track of string tension and retention, so naturally I've also been measuring the dominant frequency of the stringbed. I do this because I want to keep track of my optimal string and tension preference. And also to make sure that my stringer is not messing up on me.

There are several tuner apps for smartphones that can do this, like CarlTune for Android/iOS . It's quite easy, just strum lightly across the stringbed with your 3rd and 4th fingers like a guitar, and let it ring close to the mic on your smartphone.

The dominant frequency reading should be in the range of 1000-1300 Hz. Obviously the higher the tension and the thinner the string, the higher the frequency. From my experience, each 1 lb change in tension results in about 30-40 Hz change in frequency.

Also from my experience and contrary to previous notions, different rackets and brands do not affect the frequency as long as they are the same shape and string density. Therefore you can't compare between isometrics and oval / iso-ovals like Cabs or VZTF. Or between regular 22x22 pattern with Forza’s 96 hole monster with 24x26 pattern.

Now the purpose of this thread is to pool together in one place the various strings, tensions, and frequency readings. Hopefully this will allow us all to see how accurate and consistent our stringer is (which could be ourselves!), and also to have a common measure of understanding when someone says they’re playing with 28 lbs but in reality is only 24 lbs because their stringer has poor technique or uses a poorly calibrated manual crank machine. If you're using BG65 or VS850, this will also allow you to see how poor the tension retention is!

To achieve the highest consistency and accuracy then, please follow these requirements:
1. Isometric rackets with 22x22 pattern preferred. If not, please specify.
2. Must be only strung with ECP (electronic constant pull) machines, preferably by experienced stringers. No exceptions, otherwise you’ll pollute the data.
3. To allow for tension to stabilize after stringing, must wait for at least a week or play for a few hours before measuring frequency.
4. Zymax strings preferred, due to its wonderful tension retention property. But if other strings used, please specify how long since being strung.

I’ll start off with:

ZM62, 23x24 lbs, 1135 Hz, 2 weeks
ZM62, 22x23 lbs, 1105 Hz, 3 weeks
ZM62, 22x23 lbs, 1100 Hz, 3 weeks
ZM62, 22x23 lbs, 1085 Hz, 6 weeks
ZM65, 20x21 lbs, 1020 Hz, 2 weeks
ZM65, 19x20 lbs, 1000 Hz, 6 weeks

Please submit your data so that we all can benefit from knowing!
If there are any questions or discussions, please ask and join in.

2. @visor

What a useful & informative thread.

Perhaps, we could also include the name of the racket, since racket head shape & number of string holes in the racket do matter. Additionally, i think it is useful to list down number of usage hours and playing characteristic whether smasher at the back or controller at the front for MD. The X factor would be the quality of the game the racket being used, weather & shuttle quality & type also play some part too.

We could also measure our stringer ability versus the other stringers in the other parts of the world, by comparing the frequency, the stringer claimed tension, the tension lost rate, and number of quality hours the racket being used.

3. ^^ Re racket head shape and string density, you didn't read my OP carefully...

Also, number of grommets doesn't matter.

Yes, agree on the amount of time played and player characteristic, whether hard hitter or not... which affects the rate of tension loss.

But yep, it's interesting to note that some people claiming to play with zm62 at 26 lbs get a frequency of only 1100 Hz after a few weeks of play. This correlates to only 23 lbs from my experience.

4. Originally Posted by visor
^^ Re racket head shape and string density, you didn't read my OP carefully...

Also, number of grommets doesn't matter.

Yes, agree on the amount of time played and player characteristic, whether hard hitter or not... which affects the rate of tension loss.

But yep, it's interesting to note that some people claiming to play with zm62 at 26 lbs get a frequency of only 1100 Hz after a few weeks of play. This correlates to only 23 lbs from my experience.
Originally Posted by visor
Also from my experience and contrary to previous notions, different rackets and brands do not affect the frequency as long as they are the same shape and string density. Therefore you can't compare between isometrics and oval / iso-ovals like Cabs or VZTF. Or between regular 22x22 pattern with Forza’s 96 hole monster with 24x26 pattern.
I thought you mentioned that we could not compare the frequency of different racket frame, for example VTZF vs Ordinary Isometric frame ?
Therefore, i am thinking that mentioning racket name is necessary since VTZF & ordinary Iso head racket will not indicate same frequency given same stringer, tension, stringing machine, and type of string.

5. I used to record the frequency of each of string job s. I had a thread with a graph drawn. Let me dig it out when I go home.

6. Originally Posted by Licin
I thought you mentioned that we could not compare the frequency of different racket frame, for example VTZF vs Ordinary Isometric frame ?
Therefore, i am thinking that mentioning racket name is necessary since VTZF & ordinary Iso head racket will not indicate same frequency given same stringer, tension, stringing machine, and type of string.
Heh... guess I wasn't clear enough... but I did mention that the first requirement is that iso frames are preferred, and if not iso, then must be specified

7. Originally Posted by kwun
I used to record the frequency of each of string job s. I had a thread with a graph drawn. Let me dig it out when I go home.
Originally Posted by kwun
here are some data that illustrate it:

this is a graph of frequency (vertical axis) vs. tension (horiz axis). i measured it on a single piece of ZM62 (not a whole string bed).

Attachment 77249

if you extend the line linearly, it won't intercept at the origin. i did a curve fit of a square root plot, and it fitted perfectly.

the 25Hz/pound gradient is the gradient around where we are interested in, which is between 20-30lbs.

Interesting... I dug up one of your graphs from 2 years ago from this thread
where you measured one single length of zm62.

The data correlates directly with my frequency data on the whole stringbed!

8. Originally Posted by visor
As some of you may know, I'm pretty meticulous in measuring my equipment... (now get your mind out of the gutter)... I'm referring to my rackets.

I also like to keep track of string tension and retention, so naturally I've also been measuring the dominant frequency of the stringbed. I do this because I want to keep track of my optimal string and tension preference. And also to make sure that my stringer is not messing up on me.

There are several tuner apps for smartphones that can do this, like CarlTune for Android, and ClearTune for iOS. It's quite easy, just strum lightly across the stringbed with your 3rd and 4th fingers like a guitar, and let it ring close to the mic on your smartphone.

The dominant frequency reading should be in the range of 1000-1300 Hz. Obviously the higher the tension and the thinner the string, the higher the frequency. From my experience, each 1 lb change in tension results in about 30-40 Hz change in frequency.

Also from my experience and contrary to previous notions, different rackets and brands do not affect the frequency as long as they are the same shape and string density. Therefore you can't compare between isometrics and oval / iso-ovals like Cabs or VZTF. Or between regular 22x22 pattern with Forza’s 96 hole monster with 24x26 pattern.

Now the purpose of this thread is to pool together in one place the various strings, tensions, and frequency readings. Hopefully this will allow us all to see how accurate and consistent our stringer is (which could be ourselves!), and also to have a common measure of understanding when someone says they’re playing with 28 lbs but in reality is only 24 lbs because their stringer has poor technique or uses a poorly calibrated manual crank machine. If you're using BG65 or VS850, this will also allow you to see how poor the tension retention is!

To achieve the highest consistency and accuracy then, please follow these requirements:
1. Isometric rackets with 22x22 pattern preferred. If not, please specify.
2. Must be only strung with ECP (electronic constant pull) machines, preferably by experienced stringers. No exceptions, otherwise you’ll pollute the data.
3. To allow for tension to stabilize after stringing, must wait for at least a week or play for a few hours before measuring frequency.
4. Zymax strings preferred, due to its wonderful tension retention property. But if other strings used, please specify how long since being strung.

I’ll start off with:

ZM62, 23x24 lbs, 1135 Hz, 2 weeks
ZM62, 22x23 lbs, 1105 Hz, 3 weeks
ZM62, 22x23 lbs, 1100 Hz, 3 weeks
ZM62, 22x23 lbs, 1085 Hz, 6 weeks
ZM65, 20x21 lbs, 1020 Hz, 2 weeks
ZM65, 19x20 lbs, 1000 Hz, 6 weeks

Please submit your data so that we all can benefit from knowing!
If there are any questions or discussions, please ask and join in.
I've been considering getting a PC microphone and doing this myself... no iPhone, so I'd have to find an appropriate PC application.

9. Originally Posted by Mark A
I've been considering getting a PC microphone and doing this myself... no iPhone, so I'd have to find an appropriate PC application.
There was a program mentioned in one of the frequency threads. Had it installed once but not sure which measurement to read ...

10. Originally Posted by Mark A
I've been considering getting a PC microphone and doing this myself... no iPhone, so I'd have to find an appropriate PC application.

11. Originally Posted by MarkA 047667
I've been considering getting a PC microphone and doing this myself... no iPhone, so I'd have to find an appropriate PC application.

Originally Posted by demolidor
There was a program mentioned in one of the frequency threads. Had it installed once but not sure which measurement to read ...

Google also shows these java aplets that run in windows explorer.

12. Frequency also depends on frame size. Though it can be hard to tell, it definitely makes a difference.

It would also be interesting to see frequency differences due to different string patterns, on the same type of racquet

13. Originally Posted by demolidor
Turns out there are plenty of freeware frequency analyzers... I'll get a mic and get cracking. My first "subject" will probably be NS30.

It might be worth stickying the resulting "database"...

14. Originally Posted by zombie7
Frequency also depends on frame size. Though it can be hard to tell, it definitely makes a difference.

It would also be interesting to see frequency differences due to different string patterns, on the same type of racquet
@zombie0517 :
Yep, frame size affects frequency probably due to a change in string density. So vztf,
z slash, cabs will ping about 30-50 Hz higher, wheras
bs series (with slight pinching in at 2 and 10 o'clock) ping the same.

2 knot vs 4 knot stringing doesn't affect the frequency, from what i've
seen.

15. MX80 with @26lbs = 1143 Hz
AT900 LCW with @26lbs = 1129 Hz
AT700 with @26lbs = 1127 Hz

Some data from that RacquetTune thread.
String=BG65

Yonex VT80 w/ BG80 @ 27lbs = 1270 Hz
Victor MX80 w/ VS850 @ 27lbs = 1246 Hz

Yonex VT80LTD w/ BG66UM @ 27lbs = 1315Hz

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