I thought I might add something to this discussion I don't know if this paper has been mentioned here, but you can calculate the actual string tension on any racket. It's very accurate but also very sensitive to the variables so it can be hard to get measurements. If you do it right though you know the true tension accross different rackets. In the appendix what the paper shows is that a string bed can be modelled as an elastic membrane. Such a membrane's vibrational frequency depends on its mass and surface area while shape has very little effect (useful for us). If you take a square membrane, it vibrates at the same frequency as the average of many independant strings layed out in the same shape, which is much simpler to model. They verified this was also the case with an eliptical membrane, within 1%. So you can take advantage of that and turn it into: All SI units, so f being frequency in hz, T being string tension in Newtons, μ being string mass per unit length in kg/m and L being string length in m, which in this case is (closely) approximated by: A being the area of the racket head. So there are three things you need to measure at least reasonably accurately. - Frequency - The area of the racket head (close to the outside edge) - Mass of that type of string That's all you need but I've found it hard to hunt down string mass. Frequency we can all do given this thread Area of a racket is bit fidley with isometric heads but at least you can pull out a tape measure and get something close. String mass is really important and I've tried finding manufacturer specs to no avail. I suppose those of you who are stringers can just weight a piece. Anyway, let's do an example. I just got a VT7 (yeah, I'm no pro) and specified to string with BG80 @ 23 lbs. The frequency is close to 1050 hz. A casual measurement of the racket seems to give an area of about 392 cm^2 or 0.0392 m^2, which makes L = 0.198 m. I don't have an accurate value for string mass because I'm not about to cut the string off I can at least approximate for illustrative purposes though. I read that stringing a racket adds somewhere around 4-6 g to the racket and by my estimate it's around 9 m of string or so. That gives a string mass of roughly 0.55 grams per meter or 0.00055 kg/m. Here's a rearrangement: So, Giving us a force of 95.1 N of tension. 95.1 N / 9.8 N/kg = 9.7 kg equivalent down here on earth Or 21.34 lbs. The only problem is the huge error on my area/string numbers. It's probably 21.34 +/- at least 20%. Gotta get some good measurements. Any volunteers? There's another paper floating around that has excellent data on tension loss over time but I can't seem to find it right now. I hope someone found this interesting
[MENTION=114759]Lieu201[/MENTION] Wow, tks! Very interesting indeed! I'm not accessible to do the recalculation at the moment, but BG80 is 3.5g and length is approx 9.1m on the racket. We'll need a stringer to help us nail down accurately on the length.
I found this article extreme relevant to this thread : How the fundamental frequency of a vibrating string depends on the string's length, tension, and mass per unit length is described by three laws: 1. The fundamental frequency of a vibrating string is inversely proportional to its length. Reducing the length of a vibrating string by one-half will double its frequency, raising the pitch by one octave, if the tension remains the same. 2. The fundamental frequency of a vibrating string is directly proportional to the square root of the tension. Increasing the tension of a vibrating string raises the frequency; if the tension is made four times as great, the frequency is doubled, and the pitch is raised by one octave. 3. The fundamental frequency of a vibrating string is inversely proportional to the square root of the mass per unit length. This means that of two strings of the same material and with the same length and tension, the thicker string has the lower fundamental frequency. If the mass per unit length of one string is four times that of the other, the thicker string has a fundamental frequency one-half that of the thinner string and produces a tone one octave lower. Source : http://science.howstuffworks.com/sound-info4.htm
Frequency: ~1194Hz Racket head area: 54 inch^2 (manufacturer data; TC700) String mass NBG98: ? (two piece 22x22 instead of 22x23 as recommended) = tension? Just installed a few tuner apps on windows phone and very hard to get a reading. Across three or four of them this number roughly pops up (1192-1198 spotted along a host of nonsensical ones at ~max sensitivity). Accurate Tuner is supposed to be the best one and it (painstakingly) gives 1194-1195Hz. Taken from a long lost/misplaced (back of the closet) racket that was strung 3 years ago (@ iirc 13x14KG) and has never been used apart from a few short serves and wall hits at home after it should have settled down a bit
i'm gonna guess 26 lbs if that frequency is right off the stringing machine or 28 lbs initially if that frequency is on a racket that's strung more than 2 weeks ago
Mizuno had listed it as 54 inch^2 for this model and 56 for their (more) conventional isometric shaped models. "3 years ago" (strung at 13x14kg or 29x31lbs). Thought it might be of interest in the tension holding capacity but I will try to re-measure with the PC software Mark mentioned. To press it still feels pretty tight, comparable to BG80 at 28 or 29lbs ... so 26 might be close. Kwun listed a NBG98 at 26 with around the same frequency I saw somewhere above (so 24x26 actually it was). This is what I am working with atm (has to be set at max sensitivity to pick up the sound and as you can see this has certain consequences ) [video=youtube;pi5a0wW1jG4]http://www.youtube.com/watch?v=pi5a0wW1jG4[/video]
3 yrs ago?! Shouldn't you cut the string at such high tension if you're going to store it and not play with it for that long? Isn't it going to eat into your grommets? Not only that, but you don't know when and if the string breaks in storage, you wouldn't see it and could possibly end up with a deformed racket.
Can someone explain how I use and set up ClearTune (iphone) and how to strum the strings to get some measurements? I have next to no knowledge of musical instruments so please explain in simple terms! I had a quick go at this but the frequency seems to fluctuate quite a lot (550hz to 1300hz)... Many thanks in advance!
With the back of your 3rd finger nail, lightly strum across the stringbed to generate a solid ring, while holding the racket head close the mike. With practice it'll become easier to judge how much pressure is required. The frequency should be in the range of 950-1400 Hz for tensions of 20-30 lbs. Each lb variation is around 30-40 Hz.
Do you "pick" a string with your fingernail or do you brush across the stringbed with your fingernail? I just can't seem to get any consistent values... is it something to do with the settings? I'm in Equal Temperament mode (whatever that means) and the other settings are as default... A4 Calibration is at 440, Transposition = C. Needle damping = ii and pitch pipe waveform = sine. I have no idea what any of this means and most of my frequencies are around 400-500hz, even though they feel like around 28lb.
Not sure what I'm doing wrong but I'm struggling to get over 585hz on a racquet originally strung at 31/30 but is now probably around 27-28lb.
I've tried and tried for ages last night with a pen and fingernail and even on two different devices, still couldn't get over 600hz on any of my racquets. In fact, it seems to fluctuate between around 250-580hz. I've even downloaded several other apps, all showing low figures - although Cleartune seems to be the most consistent. I also noticed a difference in the frequency if I strum near the top of the frame or in the centre. No idea why this is... does my app need calibrating?
So strange. Make sure you're pinging close to the mike? Maybe reboot your iPhone? Or if that fails, switch to Android? And if you're consistently picking up the same frequency in that range, then that's most likely a harmonic frequency, so just double that for your actual frequency. So 580 Hz becomes 1160 Hz, which is more consistent with 26-28 lbs, depending on your string diameter.
I've no idea to be honest as my knowledge of harmonics isn't that good. If you're saying that its possible my phone is picking up the harmonic frequency and that doubling it gives the actual frequency, then I'll just take your word. Most of my strings are NBG99. Some are VS850, BG80P and NGB95.... so it's around 0.69mm mark. Oh and yes, I always ping close to the mic.
Dang it... ClearTune must have changed something with the latest update. I also get halved frequency with ClearTune on my old iPhone. I use the free CarlTune on Android and it's excellent. I see that it's also available for iOS for free, so use that and let us know how you do with it.
Glad you're getting the same result with cleartune. I was beginning to think I was going mad. I'll give Carltune a go tonight and will report back. Shame I just paid for ClearTune with no use for it now!
These are the readings I'm getting with CarlTune. But I'm getting 1736 and 1102 much more often than the others. It's better, but still not consistent enough to be useable. The strings feel like they are around 27lb now, down from 30lb. 1736 2322 2442 4186 1102
