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Expressing relative blade speed

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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 5:21pm
Update: I don't have had the time to review all my posts below yet, but I have played again with Higgs and, after all, and despite being a 7-ply blade, my impression is that it is not a fast blade (though it's advertised as being fast). Actually, it's speed is not much higher than Violin's.

Amplitude and frequency spectra of a single ball bounce in similar experimental conditions (amplitudes were normalised).

The membrane modes of Nittaku Violin and Nexy Higgs have a similar frequency, though Higgs is considerably faster. The vibration amplitude of Higgs decays much faster than Violin.

Yinhe T-7 and Tibhar Inca share a similar speed (I never played the two side-by-side, however from memory the T-7 is faster than Inca), and also a similar membrane mode frequencies. The vibration amplitude of T-7 decays much faster than Inca, though.

The speed certainly does not reflect in the amplitude of the frequency peaks.
Can anything be said about the amplitude decay rate? ConfusedGeek



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Edited by arg0 - 10/27/2017 at 3:45pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hozuki Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 5:39pm
Since the Nexy is a 7ply, it is probably stiffer than the 5ply.
That backs up my claim: The shorter the decay, the stiffer the blade.
Your observation that the Nexy faster is probably explained by the higher stiffness as well.

Therefore I argue that comparing the frequencies of blades with a similar decay time can yield more accurate results in comparing their speed.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 5:51pm
Originally posted by Hozuki Hozuki wrote:

Not so weird. I have already shown an inherent flaw in this method, which provides one possible explanation for this occurence, but nobody seemed to care.
To see whether it applies to this specific case, the full frequency chart is neccessary, though.

I'll make one more attempt at explaning it in more detail.

Blades can vibrate in multiple frequencies that can be very close together in terms of pitch and volume. This is especially evident in ALL+ Blades. Here is an example: (Hinotec ALL+)

[image removed]

Now I ask you: Which frequency would you pick to insert into the table? 1005? 1500? Or 12000?
As you can easily see, there is good potential for confusion. In fact, the first two peak freqs only have a 0.3 db difference in volume. Thus, a slight variation in blade weight, phone mic freq response or some other factor might lead to big differences between measurements of different people.

So what can we do to make things more accurate? Easy. Just don't rely on a single indicator that condenses the frequency chart into one freq peak number. Either find a better one, or use multiple indicators. Based on this, we can now all start thinking what would be suitable.
[...]

Is the Hinotek an all-Hinoki blade? If so, from experience and gut feeling I would pick 1500 Hz as the membrane mode, and 1005 Hz as a bending mode. The reason is that all multi-ply hinoki blades I measured (with the exception of Nexy Tamar), tend to have a membrane-mode frequency which is much higher than their speed class: compare with Bty Kiso Hinoki V, and TSP Hinoki Pure in my data (not all measurements in there are by me, but those are). I had a similar issue with Nittaku S-5 (all-spruce), which I returned without even testing because of the high frequency. So it must have to do with hinoki/spruce/conifer wood.

As to the double peaks, I also had this a few times, especially for 1-ply blades (Nittaku Miyabi and American Hinoki Ancient Kauri), and could not decide. I would need to look at the frequency spectra again, but if in your case I picked 1500, I suppose that for consistency, I would have to pick the higher frequencies.

As to whether and how those frequencies are related to speed, see my doubts in my previous posts. I suppose that for measuring blade speed we need some way to estimate the blade's elasticity/damping index (to use a simplified name). And most likely we'd have to do this for low speed and high speed impacts, to take non-linearities into account. Not easy to do by hand, a ball cannon would be more appropriate...

My impression is that these vibration mode frequencies are more related to the stiffness feel of the blade, than plain speed. Just, it often happens that the stiffer blades are also the faster.

Or, if they somehow represent speed, by the way we obtain these frequency, by just dropping the ball on the blade, they can at most represent speed of the blade at low impact speed.

It's late here and I cannot perform this test without waking my son, but anyone can make a quick test to see whether the frequency of the main peak varies by just dropping a ball on the blade or by hitting a ball as hard as you can with the blade? Try to grip the blade with the same strength in both cases.
Or better yet, grip the blade with low force and record the sounds of: 1) a ball dropped on the blade while you hold it losely, and 2) the same ball being driven very fast on the blade by someone while you hold it losely, if that makes sense.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 5:56pm
Originally posted by Hozuki Hozuki wrote:

Since the Nexy is a 7ply, it is probably stiffer than the 5ply.
That backs up my claim: The shorter the decay, the stiffer the blade.
Your observation that the Nexy faster is probably explained by the higher stiffness as well.

Therefore I argue that comparing the frequencies of blades with a similar decay time can yield more accurate results in comparing their speed.



Interesting point again about the decay.  I wonder if we can do much other than show the whole spectrum?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hozuki Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 6:15pm
Those are some good points you make, arg0.

Some comments:

The Hinotec just has Hinoki outer plies. But it might indeed be the special attribute of hinoki that leads to this second peak. How this affects speed, we can't say yet.

I also think it would be very helpful to measure blade frequency response at high impact, and see what changes in the frequency chart occur.

For more accurate results, the elasticity / stiffness would indeed also need to be considered. Maybe we can even approximate this by dividing the peak frequency through the decay time, as the stiffer blade feels faster (at least from low to medium impact) even if freq are the same, which can be corrected by such a formula.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 6:21pm
Originally posted by Hozuki Hozuki wrote:

Those are some good points you make, arg0.

Some comments:

The Hinotec just has Hinoki outer plies. But it might indeed be the special attribute of hinoki that leads to this second peak. How this affects speed, we can't say yet.

I also think it would be very helpful to measure blade frequency response at high impact, and see what changes in the frequency chart occur.

For more accurate results, the elasticity / stiffness would indeed also need to be considered. Maybe we can even approximate this by dividing the peak frequency through the decay time, as the stiffer blade feels faster (at least from low to medium impact) even if freq are the same, which can be corrected by such a formula.


Some practical considerations.  Whatever you come up with has to be robust (for example not too sensitive to phone microphone variation), reproducible, and easy enough to implement that non-engineers can do it.  That way it can be generally adopted. If only a small handful of people on these forums have the technical expertise to do this, it can never catch on.  It might be ok to sacrifice a little accuracy if you can get that.  Hopefully we can get something that can be useful to compare different blades within a class of bades (so it might not be a problem if you can't compare a 5-ply ALL+ wood with an OFF+ ALC blade because nobody really needs to do that).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 6:48pm
Simply and robustly estimating decay time is not simple. We could try to use HWHH (Half-Width at Half-Height) as decay time, but that's still requires human intervention and will lead to human error, unless we find an automated way to do this: I suppose that fitting an exponential function to the audio amplitude may do the trick.
Then again, we're not even sure how decay time influences speed, and we would need to have a mechanical model or experimentally validate any formula we come up with, or otherwise it's just guesswork.

Another suggestion. Put a yardstick against a wall, and drop a ball from 1m height (or any suitable imperial length) on the blade and see how high it bounces. I imagine a layman gets about 10% error in the measurement, a tt player 5% ;-) This allows to determine how much energy is absorbed by the blade or lost by friction with air and how much returned to the ball. To factor air resistance out, since working in vacuum is not an option for many, we could use tiny stainless steel balls (e.g., from small ball bearings), but not everyone has some laying around. In alternative, you're only allowed to do this test at sea level :-D.
Then again, tests would need to be performed to compare low-speed and high-speed impact.
If we want to go down this road, better build some professional testing equipment somewhere and collect money to ship blades to the facility and back to their owners...

Or, let's stay simple and let's see how far we can go with just a racket, a ball, a yardstick and a smartphone.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 6:55pm
The alternative is that people record their audio data and share the audio files so that some volunteer can analyse them. Anyone willing to create a public repository?
Also, all the relevant data should be in the file name. What about
Stiga _ Offensive Classic Carbon _ 82g (any other comment).mp3
or the like?
Mp3 is just an example, any other audio format will be fine, as supported by your recording devices.

Edit: I'm not volunteering myself Tongue


Edited by arg0 - 07/04/2017 at 6:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote book4all Quote  Post ReplyReply Direct Link To This Post Posted: 07/04/2017 at 7:57pm
Just send all blades to one people to record and analyze the results. It is more accurate and consistent. 

Notes:  I'm not volunteering myself Big smile.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slevin Quote  Post ReplyReply Direct Link To This Post Posted: 07/27/2017 at 2:27pm
From the latter part of this Butterfly article - I'm assuming Butterfly started using a similar version of this concept to express the relative speeds of its blades:

Exact measurements produce exact values for blades

Mitsuru HAYASE

Mitsuru HAYASE

2015, Butterfly introduced the “reaction” and “vibration” property as means to quantify the characteristics of a blade.

What may seem like a minor change is actually a major switch in philosophy.

Until now, blades have been charactized by a “speed” value into 5 categories (from All- to OFF+) and the feeling had to fit into 3 categories (soft, medium, hard).

For example, the 5-ply “KORBEL” blade was characterized as “medium fast” with a “soft” feeling. These values were given as a result of testing and feedback from professional players.

Vibrationswert

Vibrationswert

Mitsuru HAYASE, expert in fundamental research started to improve on this system 3 years ago:

„Advancements in digital measuring technology allows us to use more precise figures to describe blades. In the course of the last three years we were able to analyze and quantify this data.

As a result we wanted to update the “subjective” value of “feeling” given to us as feedback of professional players and use a value which can be proven and reproduced methodically. This will help customers to inform themselves on the characteristics of a Butterfly blade and we have adapted these values to all blades.”



Edited by slevin - 07/27/2017 at 2:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 07/27/2017 at 5:05pm
I know I've posted these links before, but now I do it in a different context.

These papers describe some of the equipment that can be used for a professional analysis:
http://www.sciencedirect.com/science/article/pii/S1877705812017316
http://www.sciencedirect.com/science/article/pii/S1877705814005840

I find it particularly clever when they use a thin layer of fine sand to visualise the modal lines and mode shapes. More complex and costly approaches use laser techniques for measuring distances.

Similar analysis techniques are used by ARTTE (an new Italian brand).

I don't have any insight on what equipment XIOM, ITC and other brands use for measuring their blade performance indices, but I suppose that it's not just surveys among testers.
In his previous TT blog (on a service closed by Apple), igsstern was assessing blades based on indices derived from objective measurements (he never disclosed how he measured, though). If I understood well, he was also developing blades for Adidas and now for ITC. So I assume the performance indices of ITC blades are based on similar objective measurements.


Edited by arg0 - 11/16/2017 at 1:56am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 07/27/2017 at 8:48pm
Butterfly revealed the testbed in their own magazine "Table Tennis Report" first in 2007, and started the column "Gear Analyse" in 2008 in which their testings for various setups were published.

Nonetheless, they started measuring vibrational frequency for blades far earlier than that, as I found data for the ALC series as early as 1993.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote book4all Quote  Post ReplyReply Direct Link To This Post Posted: 07/27/2017 at 11:50pm
Four Friendship/729 V-6 blades:

1) Shakehand, 1476 89.5g
2) Shakehand, 1429, 93.7g
3) C-Penhold, 1523, 81.8g
4) C-Penhold, 1476, 79.6g

Used both Nittaku 3 Star 40+ and DHS 3 Star new material D40+ balls. Both are plastic balls. The recorded frequencies are the same.


Edited by book4all - 07/27/2017 at 11:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lcsmw Quote  Post ReplyReply Direct Link To This Post Posted: 08/01/2017 at 12:25pm
Without using any of the technology in this topic, this bat is extremely fast. It is made out of burled black walnut. The blade was traced from a cypress-x blade. It was originally shake hands but too heavy with rubber on both sides. It is of a reasonable weight as a pen hold.  I made a few walnut bats using a planer in a woodshop in the early seventies. It is not plywood. The other bats had straight grain and no special playing characteristics. The circular grain pattern makes the bat very hard. You could pound nails with it. It was originally covered in Butterfly Tempest. It played extremely fast.

stevew
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cobalt Quote  Post ReplyReply Direct Link To This Post Posted: 11/08/2017 at 7:11am
I've used this to test a couple of broken bats lately.  Do you think the tone would be different to a normal bat if
1) There is a crack through the handle but its still intact though wobbly
2) The handle is snapped off completely.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slevin Quote  Post ReplyReply Direct Link To This Post Posted: 11/09/2017 at 1:54am
Added readings for Xiom Feel ZX2 and ZX3

I wish the mods would sticky the two related threads in the equipment forum - this way we don't have to search each time we want to add to the relative speed table.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote arg0 Quote  Post ReplyReply Direct Link To This Post Posted: 11/09/2017 at 4:30am
Just bookmark the link...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatt Quote  Post ReplyReply Direct Link To This Post Posted: 11/09/2017 at 9:32am
Originally posted by slevin slevin wrote:

Added readings for Xiom Feel ZX2 and ZX3

I wish the mods would sticky the two related threads in the equipment forum - this way we don't have to search each time we want to add to the relative speed table.
I 2nd that. A link to Slevin’s thread at the top of h0n1g’s would be enough though (stickies take valuable place away from the main page and should be used scarcely), then h0n1g’s could be stickied. Remember: after it’s stickied, a thread will unstick if its OP is edited.
Congrats again, It’s a rare endeavor enough to be saluted so thanks a lot to both of you for bringing something useful.
Definitely a step forward from hitting our head in a skull test. . Note that the skull test is still valid as from 2 blades with the same frequency speed, one may sound better and warmer in the skull test. There is no way I am going away from the skull test.
Have all a good day/night

Edited by fatt - 11/09/2017 at 9:42am
rl gear ( •_•)O¯`·.¸.·´¯`°Q(•_•) feedback
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatt Quote  Post ReplyReply Direct Link To This Post Posted: 11/09/2017 at 9:38am
sorry, wrong quote

Edited by fatt - 11/09/2017 at 9:40am
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