Freqmess

Programm zur Bestimmung der Saitenspannung /
program to measure string tension


This is free software



Besucher / visitors : 5021




Kommentare / user feedback

I downloaded your program, strung one of my HEAD LiquidMetal MP rackets at 66 lbs. in the mains and crosses. Using your program and a simple microphone that came with my webcam, the measured tension was 45.5 lbs. Add in the offset you suggested (22.2 lbs) and this gave me a tension of 67.2 lbs. Very close to the tension setting of my stringer while stringing the racket.

I also own a Stringmeter tension gage. Measuring my freshly strung racket with the StringMeter showed a reference tension of aprox. 48 lbs.

Therefore, I would say that your program is very accurate in measuring the actual tension of the racket (accounting for a 22.2 lb loss in initial strung tension). Well done! A big congrats on what I would call a huge accomplishment.

posted by dufferok @ TennisWarehouse forum
Very nice project and extremely useful application. Very helpful. Congratulations! I was using the first method (Audacity) for few weeks. Then I tried the second application. Both run on Dell workstation on Win2000Pro using external computer mike. Mixer device for second method was SoundMAX Digital Audio. The results were very consistent and close: 568 Hz using first method and 571Hz using second method, which corresponds to only 0.3 lb of tension difference.

Anyway, fully agree with spirit and SW Stringer the main reason to measure the string tension is to have a reference, to measure relative tension loss, to compare tension now and later (after few hours or days). The actual number doesn’t matter and we’ll never know it.

The important thing is to know what’s the reading when racquet performs perfectly (eg. 29 lbs or 51 lbs or whatever, then after 5 hrs of playing it could read 2 lbs less, so we know what’s going on).

With Marc’s PC frequency method it is accurate and takes less than 60 sec.
Mechanical Stringmeter is handy and costs $20-30 http://www.stringmeter.com/index.html
Electronic Tension Tester is $40-50 http://www.eagnas.com/maxgen1/etest.html
Gamma ERT 300 Tenniscomputer is $160 http://209.166.188.140/gammasports/daughter.cfm?ID=283


posted by mido @ TennisWarehouse forum


Inhalt / Contents

Dateien/files
Beispiel/example
FAQ
Hörpoben / audio samples
Quellen / references




Eintrag / entry Quelle / source Beschreibung / description
Programm / program freqmess-de-xp.zip (deutsch) freqmess-int-xp.zip (english) Programm (3.8 MB) Version 0.7 für Windows XP
Programm / program freqmess-de-9x.zip (english) freqmess-int-9x.zip (english) Programm (3.8 MB) Version 0.7 für Windows 98
Saitendaten / string data strings.dat Datei mit neuesten Saitendaten. Einfach runterladen und ins Freqmess-Verzeichnis kopieren. / File with latest string data. Just download this file and copy it into the Freqmess directory.
Spreadsheet zur Analyse des Spannungsverlaufs / spreadsheet to analyze tension progression freqmess.sxc (deutsch) freqmess-eng.sxc (english) OpenOffice-Format
Spreadsheet zur Analyse des Spannungsverlaufs / spreadsheet to analyze tension progression freqmess.xls (deutsch) freqmess-eng.xls (english) Excel-Format
Tutorial: Easily measuring your string tension (Tennis-Warehouse.com) Thread Thread aus dem Tennis-Warehouse-Forum zum Thema Spannungsmessung
"Bespannungshärte selber messen"-Thread (Forumsdiskussion) Thread (saitenforum.de) Thread aus dem saitenforum.de zum Thema Spannungsmessung
Bespannungshärte selber messen (alt) / Easily measuring your string tension (old) freqmess.pdf (deutsch) freqmess-eng.pdf (english) Artikel der beschreibt wie man mit einem normalen PC die Bespannungshärte auf seinem Schläger messen kann. / Article, that describes how to measure string tension with your PC and Soundcard.
Bespannungshärte selber messen II (alt) Messung Erste Gedanken zur Methode.


Standard µ-Werte / default µ-values


Spezielle µ-Werte / specific µ-values


Data from all kinds of strings needed ! I'm glad about every µ-value of a tennis-string. See below for details on measuring µ of a string. Please send string data (string-name,diameter,µ,length of string-set,weight of string-set) to me via e-mail : marc-roettig@web.de.


Saite / string Durchmesser / gauge µ Massedichte / mass-density
String data kindly supplied by SWStringer
Prince Synthetic Gut Soft 16 1.479
Prince Synthetic Gut Original 17 1.335
Gamma TNT 17 1.326
Babolat Super Fine Play 17 1.330
Prince Synthetic Gut Soft 17 1.294
Gosen OG Sheep Micro 17 1.319
Klipper Synthetic Gut w/UltraFibre 18 1.129
Prince Synthetic Gut w/DuraFlex 18 1.129
Kirschbaum Touch Turbo 1.30mm 1.677
Luxilon BigBanger Orig. 1.22mm 1.739
Luxilon TiMo Banger 1.22mm 1.592
Gosen Polylon Ice 1.25mm 1.748
String data kindly supplied by mido
Signum Pro Poly Plasma 1.23mm / 17 1.65
Signum Pro Poly Plasma 1.18mm / 18 1.52
Signum Pro Poly Megaforce 1.19 mm / 18 1.52
Babolat Pro Hurricane 1.25 mm / 17 1.69
Klip K-Boom 1.25 mm / 17 1.64
LaserFibre Synthetic Gut Classic 1.30 mm / 16 1.59
Signum Pro Ultra Power SF 1.28 mm / 16L 1.58
Signum Pro Fiber High Tec EXP 1.24 mm / 17 1.56
Klip Excellerator 1.29 mm / 16 1.47
Wilson Sensation 17 1.25 mm / 17 1.39
Prince Synthetic Gut w/Duraflex 1.30 mm / 16 1.51


Beispiel / example :

Ich hab meinen Head iPrestige MP mit ner PP Plasma Power 1,18mm @ 26/25 kg bespannt. Direkt nach dem Bespannen hab ich mit meinem Programm Freqmess eine reale Spannung von 14.71 kg bestimmt. Das heisst ich habe grob gerechnet 25.5 kg - 14.7 kg = 10.8 kg nach (und während) dem Bespannen verloren. Dieser Verlust ist völlig normal, da die volle Zugspannung nie ganz auf die Saite übertragen werden kann. Für den Verlust sorgen vor allem die Reibung der Saiten, Brechen von Molekülbindungen des Saitenpolymers,etc. Saiten haben direkt nach dem Bespannvorgang bereits ungefähr 35 % der angelegten Zugspannung verloren. Diesen Verlustwert muss ich nun einfach bei weiteren Messungen dieses Schlägers auf die gemessene reale Spannung hinzuaddieren um auf die absolute Spannung im Zuggewicht-Bereich zu kommen [20,30] kg.

Eine Woche nach Bespannen der Saite habe ich eine reale Spannung von 12.61 kg mittels Freqmess erhalten. Ich addieren den Offset von 10.8 kg hinzu und erhalten eine absolute Spannung (im Zuggewichts-Bereich, also der Bereich der uns geläufig ist) von 23.41 kg.

Die Saitenspannung halt also um 2.09 kg nachgelassen. In dem Zeitraum war ein 2 h Spieltest enthalten.

Jeder der also mittels des Programms absolute Spannungen im Zuggewichts-Bereich erhalten will, weil dieser Wertebereich uns geläufiger ist, muss einfach sein persönliches Bespannungs-Offset bestimmen, und diesen Wert einfach auf den Output von meinem Programm hinzuaddieren. Dann bekommt er einen absoluten Spannungswert, also das Gewicht, daß man an seiner Bespannmaschine einstellen müsste um direkt nach dem Bespannen eine Saitenspannung zu bekommen, wie sie gerade auf dem gemessenen Schläger vorliegt.

Hinweis: Spannungsdifferenzen können problemlos auch mittels realer Spannungen bestimmt werden. Eine Transformation der realen Spannung in absolute Spannung ist somit nicht nötig. Man kann jedoch auch mit der absoluten Spannung Spannungsunterschiede messen, da die Transformation linear ist.

I strung my Head iPrestige MP with a Pro's Pro Plasma Power 1,18mm @ 26/25 kg. Directly after I finished stringing, I measured with my program Freqmess a real tension of 14.71 kg. So I lost 25.5 kg - 14.71 kg = 10.8 kg of tension during and after stringing. This is perfectly normal, as the full pull-tension never makes it completely on your strings, due to factors like friction,stress-relaxtion of strings and so on, that cause tension-loss. Strings have generally lost approx. 35 % of the applied pull-tension right after finishing the stringing-process. This tension-loss value has to be added to the tension results of Freqmess to get tensions in the range of pull-tension [20,30] kg.

One week after putting the string on my racket, I measured a real-tension of 12.61 kg with Freqmess. Adding the tension-offset of 10.8 kg to the real-tension value yields a tension-value in the pull-tension range (which we're more used to) of 23.41 kg.

The tension dropped by 2.09 kg after 1 week, which included a 2 hour playing test.

Everyone who wants to calculate absolute tensions in the pull-tension range, just has to determine his personal tension-loss offset by measuring the real-tension right after completing the stringing-job and substracting it from the applied pull-tension. This offset has then to be added to the real-tension values that Freqmess calculates to get absolute tensions in the pull-tension range.

Note: Tension difference can easily measured in the real-tension range, for these no transformation is needed. But of course in the absolute tension range too, as the transformation is linear.


FAQ

Q: Why are the tensions that Freqmess calculates so low, and not within the range of [20,30] kg ?
A: After you have finished your racket with let's say 26 kg, you don't have 26 kg of tension on the strings anymore. Due to factors described below, you will loose approx. 10 kg of your applied pull-tension during and after the stringing process. This is a fact, consult Cross, R., & Bower, R. (2001). Measurements of String Tension in a Tennis Racket. Sports. Eng, 4, 65-175 for more information. So the frequency-method Freqmess uses, can only measure the tension that is still left on your strings (aka real-tension) and not the formerly applied pull-tension (aka reference tension) of the stringing machine. But one can transform the real-tension measured by Freqmess, via adding the tension you lost during and after stringing. This lost tension or tension-offset is defined as difference between the applied pull-tension and the real-tension right after the stringing process. Now to get pull-tension values for your strings, which we're more used to, just add the tension-offset to the real-tension calculated by Freqmess. As an approximation for poly-strings you can also use a tension offset of 10 kg or 22,2 lbs. But for monitoring string-tension progression, the real-tension works well and no conversion needs to be done, as your just interested in tension differences, ie. you want to know the time when you've lost 2 kg of tension.
Q: What effects during/after stringing cause that big tension loss of up-to 35% after stringing ?
A:
  • stress relaxation : The force that acts on the string due to the tension causes molecule bonds of the string-polymer to break. This causes a dramatic loss of tension during and directly after stringing. Overall the stress-relaxation causes approx. 3 kg of tension loss.The tension loss due to stress-relaxation is higher for polys than nylons.
  • friction : When stringing the crosses you loose some tension due to friction between the mains and the crosses. Friction accounts for roughly 2.5 kg of loss in tension.
  • racket deformation : During stringing the racket-head suffers under deformation due to the tensioning procedure.
  • machine : The pull-arm of the stringing-machine is not in the same plane as the strings are. They are displaced by approx. 15 degrees. So you loose some tension here, as they're not co-linear. 1-2 kg are lost here.
  • knot-tying : When you finish your stringing-job and tie off the knots you'll also loose (depending on your tying-method) some tension.
  • minor inconsistencies : pulling two string lanes at once, distraction during stringing, ..
So overall you may loose roughly 10 kg from your pull-tension. As you can see from the list of contributing factors, the tension-loss also depends on the stringer : Is his work accurate ? Does he use sophisticated equipment? And so on. But no problem, you can calculate your personal tension-loss value and add this offset to the values that the Freqmess program gives you.
Q: I don't want the real tension, I want the corresponding pull-tension. So how can I calculate that obscure personal tension-loss(tension-offset) value ?
A: Right after stringing measure via Freqmess the real-tension that made it onto your strings and substract that real-tension from the applied pull-tension. Now you've got your personal tension loss or tension-offset. This offset has to be added to the later-on measured (via Freqmess) real tensions to get tension-values in the corresponding pull-tension range. This whole transformation procedure is in so far useful, as we are more used to the pull-tension range, as that is the value we instruct our favorite stringer to string our racket with.
Q: Would this program require different information for 17 gauge Rip Control, 17 gauge Lightning XX, 17 gauge Timo Banger, 17 gauge Gamma Infinity, 17 gauge XYZ ?
A: The only parameter in the formula that is affected by the type of string is the mass-density µ of the string. One might argue that the microscopic properties of the string (i.e. nylon,gut,poly) must have some influence on the frequency of the vibrating strings. But Cross and Bower conclude in their paper that "provided that the vibration amplitude is small, then the vibration frequency of a steel string is the same as that of a nylon string of the same mass density µ, the same length and at the same tension." So in the frequency method primarly the mass of the string counts, not its microscopic structure. So you only need to calculate the mass-density of the mentioned strings and use these density-values in the formula. Or just take the default values from the table above.
Q: How can I calculate mass-density µ of my favorite string xyz ?
A: When stringing the next time, just weight your prepared string-set (for example you get a weight of 22 g) and divide its weight by the length of the string-set (for example 12 m). You'll receive a mass-density µ=1.83 . [Strictly one also has to consider the extension of the string when pulled. Polys extend by about 4% and Nylons bs 9-15%. So µ should be somewhat lower.]
Q: Where does string gauge come into play ?
A: String Gauge is factored into the mass-density term, as the mass-density term µ can be re-written as µ = σ * π * (d/2)² where d is the diameter (gauge) of the string and σ the (volume) density.
Q:Does one have to have a consistent method of "plucking" the strings in a certain way to reproduce consistent frequency?
A: I suggest to hit the center of the string-bed firmly with the heel of your hand or with a "plucking-device" like a small hammer. Just make sure that the sound of the vibrating strings is quite loud and not too faint.
Q: Doesn't the type of microphone used can also effect the reading?
A: I use a vanilla-type microphone, and it works perfectly. You can even use the mic of your headset for internet-telephony.
Q: I can't reproduce the frequency values, when doing several measurements. I get lots of different frequency-values. Whats wrong ?
A: Make sure your microphone recording level is above 80 percent in the Windows Audio Mixer. Also make sure that you generate a quite loud sound of the vibrating string (i.e. do not hit the strings too weak).


Hörproben / audio-samples

Eintrag / entry Quelle / source
Head iPrestige MP (98 in²) @15.4kg Poly 1.28 mm mp3
Head iRadical MP (98 in²) @12.45kg Poly 1.25 mm mp3
Wilson HyperHammer 3.6 (115 in²) @9.85 kg Poly 1.25 mm mp3
Wilson Triad 5.0 (98 in²) @13.48kg Nylon 1.3 mm mp3


Quellen / references :

Cross, R., & Bower, R. (2001). Measurements of String Tension in a Tennis Racket, Sports. Eng, 4, 65-175
Link to Article


© Marc Röttig 2005