Program to measure string tension

[MarcR]

Hi,

I coded a little program that takes over the measurement of your string-tension.
You just have to prepare your microphone under XP for recording in the
Windows Audio Mixer, unless it's not already properly installed.
Then just launch the program freqmess.exe enter your racket and string
data and click Record. Then hit your strings once and bring the string-plane near
the microphone. Wait.
The tension T will then be displayed in the field T.

You can get the zip-file of the program via
http://www.tennis-altensteig.de/marc/freqmess-eng.zip

Remember the calculated tension is the real tension on your racket, not the
pull-tension that was used to put the strings on. The tension will decrease
by up to 40 percent minutes after stringing.

With my stringing-jobs with polyester I usually loose about 10 kg of tension
(depends on how accurate one does stringing and what strings he uses), so to
convert the real tension in the range of pull-tension I just add up 10 kg
or 4.5 lbs, respectively. The proper procedure would be to use the program
to measure real tension right after finishing your stringing-job and calculate the difference
between pull-tension and measured real-tension and to add this offset to
later real-tensions that were calculated with the program.

NOTE: Before recording the string sound remove string-dampeners.

Further details @ http://tt.tennis-warehouse.com/showthread.php?t=47260&page=1&pp=15

Greets Marc

 

[barry]

Very Clever! Does the tension very using thicker string? (16 & 17 gauge)

 

[SW Stringer]

The constant mu, (or density) in grams per meter takes into account the gauge and material composition (ie, nylon, polyester, zyex, etc.). See Marc's previous posts for the equation and how it is used.

 

[ffrpg]

What a neat program. My palms hurt now. I'm curious, what would you do type in for mu if you have a hybrid (Poly mains with syn gut crosses)?

 

[MarcR]

@ffrpg

I would take the mean-value of main-strings mu1 and the cross-strings mu2.
In the end it's the weight of the vibrating strings that count. And to take
the mean seems to be not too foolish. Maybe one can even weight the
main-strings mu a bit higher when taking the mean, as they are longer than
the crosses. So maybe something like

mu(hybrid)=(w1*mu1+w2*mu2)/2

Where
w1 = length(crosses)/L ,
w2= length(mains)/L and
L=length(crosses)+length(mains) .

I'm always wondering how the electronic measuring devices like the ERT300
acquire the racket data, especially mu. And how they convert the measured
real tension-values in the corresponding pull-tension range.

I once did a hybrid stringing on my old Head Prestige Tour, Poly in the mains
and Nylon in the crosses. As I tried to measure the frequency I couldn't
manage to get a sound from the strings. It seemd the sound fainted to
quickly. Maybe anyone out there already measured a hybrid stringing-job, and
has made some experiences.


Greets Marc

 

[matchpoints]

Instead of using the palm of your hand, why not use another racquet or like a small hammer and tap the string bed to make it resonate better. I suspect the palm to absorb some of the energy due to it's cushioned surface.

 

[SW Stringer]

MarcR says: "As I tried to measure the frequency I couldn't
manage to get a sound from the strings. It seemd the sound fainted to
quickly."

matchpoints replies: " . . . why not use another racquet or like a small hammer and tap the string bed to make it resonate better."

I agree, generating a higher amplitude 'ping' will help. I've bounced a golf ball off the string bed to get a louder thud. But the most important trick is to get the microphone right up next to the string bed - ie within an inch or two - that gets the most energy into the microphone. You can also "Amplify" the signal with the Effects menu in Audacity.

 

[MarcR]

I just tested this old racket with the hybrid.
I excited the string plane with the heel of my hand
as usual. The sound was still hardly recognizeable,
but the programm measured the frequency without
problems. You just have to bring the string plane very near
to the mircophone.

I also tested on another racket the use of the hand,hammer and
stick to excite the string-plane. All methods yielded a frequency
of 595+-0.25 Hz. So the effort of using a hammer is not really needed.
Just use the heel of your hand, thats enough =)

Greets Marc