How to measure blade speed?

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Ugh, the very moment hard-headed engineer posted "Why aren't there any 5000 Hz blades?", those who have studied/done modal analysis died inside.
Zeio has been one of the biggest sources of disinformation on any of the TT forums.
Zeio. Why don't you explain reduced mass. You posted a pdf about this on mytt.
Do I need to find the post on mytt where you calculated the speed of the ball after contact was lower than the speed of the paddle?
That occurred because zeio used the conservation of momentum formula alone instead of the speed after impact formula that combines the conservation of momentum and the coefficient of restitution.

So why aren't there 5000 Hz blades?
The forum wants to know.
zeio, tell us.
Does it really make a difference?

BTW, I am much more than a hard-headed no nonsense curmudgeon engineer. I am a very successful one and a entrepreneur. Do you think I only pick on TT forums? Engineering forums have been criticized by me. Professor are my favorite targets. Yet no one has proved me wrong. I doubt any of your TT heroes have made as much money as I have. I solve problems that other can't and I provide solutions and answers that others haven't.
Zeio can give me a red card but he can't take away my green backs. I am probably the richest person on this forum.

You guys have no clue. Most of you have flawed thinking or are paying too much to myths . The TT manufacturers lie. The equipment will not save you.
 
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Every *bleep* blade can be a 5000Hz blade and beyond! Every continuous system has an infinite...no, just forget it. I've posted the answer long ago. I'm done wasting time on you. You can't *bleep* loop. You can't *bleep* move. Over the decade, the only analogies I've learned from you are:

Bounciness = coefficient of restitution;
Shot speed = speed after impact(*bleep* speed. It should be velocity, the proper physics term for speed. Velocity is a *bleep* vector quantity, with magnitude and direction. Speed is just a scalar quantity, MF!)
Throw angle = ratio of tangential-to-normal COR

That's *bleep* it! Mythbusting? LMAO!
 
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So why aren't there 5000 Hz blades?
The forum wants to know.

Because competitive table tennis has rules.

It's quite possible in this big wide world, where plenty of people don't care about formal competitive rules, materials and blade geometry permitting, a 5kHz blade exists. I'm sure it would be very fast, something very close to a perfectly rigid object, heck it might even be a material with better elastic properties than either the ball or the rubber, and perform even better than the theoretical perfectly rigid object (wouldn't even need to be very stiff in that case!).

But given that people who actually care about official competitive rules are limited to blades made of, at least 85% by thickness, natural wood. And that practical considerations for actual use limit our creativity on size/shape of the blade as well as the material for that other 15%, that's why we don't talk about 5000Hz blades.

The forum doesn't want to know, those on the forum who know enough about it to care, are also capable of a modicum of common sense to answer this question themselves. Which I think, is the point of Zeio's critique.

BTW, I am much more than a hard-headed no nonsense curmudgeon engineer. I am a very successful one and a entrepreneur. Do you think I only pick on TT forums? Engineering forums have been criticized by me. Professor are my favorite targets. Yet no one has proved me wrong. I doubt any of your TT heroes have made as much money as I have. I solve problems that other can't and I provide solutions and answers that others haven't.
Zeio can give me a red card but he can't take away my green backs. I am probably the richest person on this forum.

I don't think you are going to find much sympathy for that line of argument, most people outside of the US, and probably even most people inside it, don't have that fetishism for money making and "entrepreneurship". It's nice if you have and/or make a lot of money(genuinely), but it doesn't make it a valid argument on technical issues. Ability to make money, is in fact, not the standard of measurement for correctness in ... just about any technical field.
 
Quality of life does not depend on money mass, but on its value.
500 000 usd annual salary is a good stake for a doctor in US, but a doctor with the same income in Bulgaria can live 10 times better.
We have such a guy in the club, 60+ old, a very nice person, who would never mention the differences in peoples' wealth status, and what is more important - he has a bat and he plays table tennis.
 
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It doesn't have to do with the rules. The duration of impact(dwell time, FFS) typically encountered in table tennis just won't excite the modes that are anywhere close to 5000Hz. But with a suitable impact hammer that can produce a broad bandwidth, you can excite ALL of the modes. Therefore, even a premade can be a "5000Hz blade." The dwell time is the deciding factor here.
 
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It doesn't have to do with the rules. The duration of impact(dwell time, FFS) typically encountered in table tennis just won't excite the modes that are anywhere close to 5000Hz. But with a suitable impact hammer that can produce a broad bandwidth, you can excite ALL of the modes. Therefore, even a premade can be a "5000Hz blade." The dwell time is the deciding factor here.

A friend of mine recently excited ALL of the modes of his bat ;)
 
It doesn't have to do with the rules. The duration of impact(dwell time, FFS) typically encountered in table tennis just won't excite the modes that are anywhere close to 5000Hz. But with a suitable impact hammer that can produce a broad bandwidth, you can excite ALL of the modes. Therefore, even a premade can be a "5000Hz blade." The dwell time is the deciding factor here.

He's obviously talking about a blade having a primarily 5000Hz response on a sharp impact.

It's a fundamental property of the blade shape and material (well the blade/rubber/sponge system since they are attached). Also technically depends on where/how it's being held/clamped.

So in this case dwell time, and a suitable hammer are irrelevant. You might be able to get it to vibrate at 5000Hz off a single impact, but it will always vibrate at whatever it's dominant mode(s) is more. You arn't going to excite a primarily 5kHz vibration in the bat short of literally just shaking the thing at 5kHz.

The other modes of mechanical resonance are really only going to be dominant when you have excitation at a frequency near it's other modes, so are only relevant when your excitation is periodic. For a single impact perturbation, you just get the object mostly vibrating at the primary mode.

This brings us to the other problem. All these frequencies (at least of the blade), even the natural frequency, are largely irrelevant to the issue of speed.

Mechanical resonance is a thing. But it's primarily about energy storage. This is why it's relevant when forces either happen periodically, over a long time (eg Tacoma Narrows bridge), or when there is more than a single impact event, and energy from a previous impact(s) is still stored in the system before the final impact (eg Angers bridge, springboard or trampoline).

We can obviously rule out the energy storage component, as table tennis is about single impacts between bat and ball where all stored energy in the bat is released or wasted before next impact.

Which leaves us with the part of mismatched phases. This seems relevant at first, eg if you stand on a springboard until you and the springboard are both at rest, then jump off it once, you will get significantly less height than if you jumped off the ground because the springboard will absorb some of the energy of you pushing off.

The problem being, given that you are not allowed to preprime your springboard for this hypothetical (since you don't get to impact that table tennis ball twice) and therefore cannot use the springboard to actually store useful energy. Then in fact any impact is modeled by jumping from rest, on a springboard-person system at rest.

As you apply force in your jump, the force goes to deforming the board further, until the point that the restitutive force is equal to the force you apply pushing on the board, at which point the board cannot deform any further, and you start to push off, once you build enough velocity relative to the now stationary board, you lift into the air, after which point the board no longer affects you.

As you can see, in this scenario, phase matching is impossible. At the point of departure, the board is in fact acting as a stationary platform. The faster the resonance of the board (or the more resistant it is to deformation) the sooner you lift off it but it is still acting as a stationary platform at the point of lifting off, irrespective of how long/far into it's deformation it takes to get to this point. The only thing that changes is how much of your energy of your jump it has wasted to get to that point. There is nothing you can do in terms of timing to make this jump more efficient, the board is passively waiting there for you to complete your jump.

So in the end, the frequency of a springboard/blade is pretty much irrelevant. You can't actually phase match 2 objects that have a speed but are otherwise passive in a collision. All you can do is make sure that the most elastically efficient components take most of the deformation.
 
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The mode we measure when we do the ball bounce is the 6th, the first and fundamental mode is usually around 100hz for a commom blade, so it will take a lot to get a fundamental of 5k Hz.

But it seems that the point is still not clear. We are not using frequency to estimate speed. We are using frequency to quickly and easily estimate stiffness! Then we establish comparisons with the stiffness of other blades that are slower or faster. Is this so hard to comprehend? It's more than clear and established that frequency and stiffness aren't the only indicators of the speed of a blade.

You keep bringing deformation, oscillation, COR, rubbers, ball and whatever into the mix, when they are irrelevant to this exercise, since all we want is to determine the stiffness. Stiffness is an intrinsic properties and depends solely on the physical properties of the blade.
 
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The mode we measure when we do the ball bounce is the 6th, the first and fundamental mode is usually around 100hz for a commom blade, so it will take a lot to get a fundamental of 5k Hz.

But it seems that the point is still not clear. We are not using frequency to estimate speed. We are using frequency to quickly and easily estimate stiffness! Then we establish comparisons with the stiffness of other blades that are slower or faster. Is this so hard to comprehend? It's more than clear and established that frequency and stiffness aren't the only indicators of the speed of a blade.

You keep bringing deformation, oscillation, COR, rubbers, ball and whatever into the mix, when they are irrelevant to this exercise, since all we want is to determine the stiffness. Stiffness is an intrinsic properties and depends solely on the physical properties of the blade.

Having just read the papers Langel linked, it appears that the 6th, or (0, 2) in the eliptical plate nomenclature, is actually the one with the biggest response anyway. It appears the fundamental mode (1, 0) just doesn't have that much amplitude.

Also, I think everyone agrees with the fundamental premise that stiffness basically equates to a faster (bouncier) blade. The argument seems to have evolved into whether there may be certain frequencies of oscillating that can cause phase matching issues.

My last post was pointing out that when it comes to a collision of 2 basically ballistic (the bat is not perfectly ballistic, but it's close enough) objects, where periodicity is not involved. Resonance, and consequently phase matching is actually an irrelevant concept. It'll tell you how the objects are vibrating after the collision, but won't tell you anything useful about the collision itself.
 
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Also, I think everyone agrees with the fundamental premise that stiffness basically equates to a faster (bouncier) blade.
Yes, because stiffer blades with vibrate with lower amplitudes and therefore absorb less energy.
See the formula for energy above.
I posted a link to how the COR of a TT ball is tested. The TT ball is bounced off of steel because steel does not absorb much energy.

The argument seems to have evolved into whether there may be certain frequencies of oscillating that can cause phase matching issues.

My last post was pointing out that when it comes to a collision of 2 basically ballistic (the bat is not perfectly ballistic, but it's close enough) objects, where periodicity is not involved. Resonance, and consequently phase matching is actually an irrelevant concept. It'll tell you how the objects are vibrating after the collision, but won't tell you anything useful about the collision itself.
The arguments is that you can't compute the energy left in the blade after impact.
You have ignored the Toxic 5 video where it is obvious that the ball has impacted the paddle and bounce back out of phase with the blade. That is one reason why the Toxic 5 is so slow.

You have solved nothing.
The thread is about "How to measure blade speed?"
You haven't shown how to do it.
Show us a formula!

The best way is to just bounce balls off the blade and calculated a coefficient of restitution.
A comparison can be made of the speed of the ball before and after impact. Measuring the speed just before and after impact is best because it minimizes the effect of air resistance.
I can use the Toxic 5 video to measure how far the ball moves over 10 frames to get a good estimate of the speed before and after impact.
If a ball is dropped the speed can be roughly calculated by measuring the ratio of the ratio of the rebound distance divided by the distance dropped and take the square root. I say roughly because it ignores air resistance.
 
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Guys I am re-reading this thread including the references. I want to thank the OP and all of you for posting very much, without exception, and ignoring some minor personal fight-backs. Honestly I am lost, but I like it. "Learning occurs" as Carl so hilariously put it in another thread. Or perhaps may occur in my case. Please continue.
 
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The arguments is that you can't compute the energy left in the blade after impact.
You have ignored the Toxic 5 video where it is obvious that the ball has impacted the paddle and bounce back out of phase with the blade. That is one reason why the Toxic 5 is so slow.

That's quite literally not the argument. Noone is suggesting to compute the energy in the blade after impact.

You have solved nothing.
The thread is about "How to measure blade speed?"
You haven't shown how to do it.
Show us a formula!

Why would this even involve a formula? It's literally how to MEASURE blade speed.

To take the question literally, it would be to take high speed camera footage of a person swinging the blade, then calculating the speed the blade reaches.

To take the question for what it means, just do the bounce test, which at several people, including both of us have already said.

All that stuff about frequency, is in response to, in your own words:

The point is that the spring board is "tuned" to the divers impact. Why aren't there any 5000 Hz blades?

The next thing to think about is spring board divers. If they adjust the spring board so it is too stiff or too compliant they will not get the best height from their jump.

This is what I am trying to get at with my spring board examples. The ball, rubber and blade all compress or bend. If they don't expand or restore shape at the same time in phase then some of the energy will be lost or cancelled.

These all allude to or are outright references to mechanical resonance. Mechanical resonance however, requires periodicity. A single collision of 2 approximately ballistic objects does not have any element of periodicity, rendering 'tuning' and being 'out of phase' irrelevant.

Just doing a bounce test (or a series of them over different impact speeds), is indeed the best and most straight foward way to measure how fast the blade is.

However, the contention that the higher the frequency, and therefore more implicitly the stiffness of the blade, the faster it is, appears to be fundamentally correct.

To quote the very Tiefenbacher paper you quoted:
'For bare materials the more stiff the material is the bigger is Epar. The absolute fastest "wood" was a massive plate of marble.'
 
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For bare materials the more stiff the material is the bigger is Epar:
Good, at least one person has read the Tiefenbach pdf.
Yes, but that means the amplitude of oscillations is small doesn't it? No one mentioned amplitudes until I did above.

I assumed the OP wants to know the coefficient of restitution of the ball and blade impact, not how fast the blade was moving. The Tiefenbacher document explains that he used video with a 500 Hz strobe to measure the the speed of the ball before and after impact. Then one computes the COR by dividing the speed after by the speed before impact. The COR is something that can be compared. I have posted the Tiefenbacher document many times over the last 12 years. Most ignore it but it tells the only practical way to measure the "speed of the blade". The OPs question was answered many years ago. The COR can't be measured by frequencies. There are too many of them and they may not be in phase like in my toxic 5 video.

All this stuff about frequencies is just a distraction. It doesn't answer the question but frequency alone doesn't determine the speed of the blade nor can it be used to calculate the COR even if the amplitude is known. My asking about why there aren't 5000 Hz blades was just to see if anybody could come up with a good answer. basically the woods are not hard enough.

BTW, lignum vitae is the hardest wood and would make for a very fast and stiff blade. Lignum vitae is also very expensive.

I have a high speed camera and can measure the speed of the ball before and after contact. I have a high speed camera that can easily capture video at 2000 fps. The grainy toxic 5 video was taken with my old high speed camera at 2000 fps. My new one is much more light sensitive and records in color.
 
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He's obviously talking about a blade having a primarily 5000Hz response on a sharp impact.

It's a fundamental property of the blade shape and material (well the blade/rubber/sponge system since they are attached). Also technically depends on where/how it's being held/clamped.

So in this case dwell time, and a suitable hammer are irrelevant. You might be able to get it to vibrate at 5000Hz off a single impact, but it will always vibrate at whatever it's dominant mode(s) is more. You arn't going to excite a primarily 5kHz vibration in the bat short of literally just shaking the thing at 5kHz.

...

That's because he doesn't know what he's talking about.

Ah, folks need a basic understanding of modal analysis before this can go on. I give up here.
 
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Good, at least one person has read the Tiefenbach pdf.
Yes, but that means the amplitude of oscillations is small doesn't it? No one mentioned amplitudes until I did above.

Because it is literally irrelevant. The oscillations are all losses, amplitude is only useful for us if we wanted to actually calculate how much energy we are losing to vibration in the blade.

But since you would need to know all the amplitudes in every significant mode, and even then, vibrations in the blade are far from the only source of loses, everyone has the common sense to know you arn't going to be calculating the COR via removing all the losses, and therefore no one has any practical reason to know the amplitudes at all. You are the only one to bring it up, because it's completely irrelevant.

I assumed the OP wants to know the coefficient of restitution of the ball and blade impact, not how fast the blade was moving. The Tiefenbacher document explains that he used video with a 500 Hz strobe to measure the the speed of the ball before and after impact. Then one computes the COR by dividing the speed after by the speed before impact. The COR is something that can be compared. I have posted the Tiefenbacher document many times over the last 12 years. Most ignore it but it tells the only practical way to measure the "speed of the blade". The OPs question was answered many years ago. The COR can't be measured by frequencies. There are too many of them and they may not be in phase like in my toxic 5 video.

All this stuff about frequencies is just a distraction. It doesn't answer the question but frequency alone doesn't determine the speed of the blade nor can it be used to calculate the COR even if the amplitude is known. My asking about why there aren't 5000 Hz blades was just to see if anybody could come up with a good answer. basically the woods are not hard enough.

BTW, lignum vitae is the hardest wood and would make for a very fast and stiff blade. Lignum vitae is also very expensive.

I have a high speed camera and can measure the speed of the ball before and after contact. I have a high speed camera that can easily capture video at 2000 fps. The grainy toxic 5 video was taken with my old high speed camera at 2000 fps. My new one is much more light sensitive and records in color.

Not everyone has a high speed camera, people with high speed cameras might not have a lot of blades, people with both of these may not have the time nor inclination to either do the grunt work, or be willing to release the results to the general public.

Judging from... not having ever seen or heard of a documents listing a bunch of blades and their CORs, either a a singular impact speed or at multiple. Then it's clear those factors havn't come together, and is pretty difficult/impractical to put together.

People however have smartphones, and collectively, people have just about all the commercial blades, so if you crowdsource the data... suddenly this is a lot easier to put together.

But with crowdsourcing, you need to work with what people have access to. As it turns out measuring ball speeds requires equipment people in the general public don't have access to.

Given that stiffness does appear to be a pretty good indicator of "speed", and the frequency of the membrane mode does appear to be a good indicator of stiffness. That renders a crowdsourced database of blades and their frequencies pretty nifty.

I don't think anyone is saying this is a better experimental, or measurment setup than just doing a bounce test. But unless you or someone else with a high speed camera wants to measure bounce speeds of a large cross section of commercial blade market, and then release the results, then knowing the frequencies of these blades, and inferring their relative stiffness (at least to the point that blade a is stiffer than blade b, but less than blade c) is the best we have?
 
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Finally, Thank you!

Bounce tests won't cut it either unless you can shoot balls at the blade at various speeds. We are dealing with an orthotropic material, so the deformation curve isn't linear. This means that different initial drop heights will produce different bounces depending on the type of blade. Let's take an outer carbon balsa blade for example. Stiffness is very big, so the energy required to longitudinally deform the blade is also very big. As you increase impact speeds you'll reach the limit of longitudinal deformation and start having out of plane deformation. The soft balsa core will kick in and you'll have energy loss. Basically this means a high reaction for a low effort shots and low reaction for high effort shots. I think everybody that played with a blade of this type can confirm the loss of power that happens away from the table, I don't need formulas or equations for that. This is what I meant in the beginning when I said that speed was more like a curve.


Because it is literally irrelevant. The oscillations are all losses, amplitude is only useful for us if we wanted to actually calculate how much energy we are losing to vibration in the blade.

But since you would need to know all the amplitudes in every significant mode, and even then, vibrations in the blade are far from the only source of loses, everyone has the common sense to know you arn't going to be calculating the COR via removing all the losses, and therefore no one has any practical reason to know the amplitudes at all. You are the only one to bring it up, because it's completely irrelevant.



Not everyone has a high speed camera, people with high speed cameras might not have a lot of blades, people with both of these may not have the time nor inclination to either do the grunt work, or be willing to release the results to the general public.

Judging from... not having ever seen or heard of a documents listing a bunch of blades and their CORs, either a a singular impact speed or at multiple. Then it's clear those factors havn't come together, and is pretty difficult/impractical to put together.

People however have smartphones, and collectively, people have just about all the commercial blades, so if you crowdsource the data... suddenly this is a lot easier to put together.

But with crowdsourcing, you need to work with what people have access to. As it turns out measuring ball speeds requires equipment people in the general public don't have access to.

Given that stiffness does appear to be a pretty good indicator of "speed", and the frequency of the membrane mode does appear to be a good indicator of stiffness. That renders a crowdsourced database of blades and their frequencies pretty nifty.

I don't think anyone is saying this is a better experimental, or measurment setup than just doing a bounce test. But unless you or someone else with a high speed camera wants to measure bounce speeds of a large cross section of commercial blade market, and then release the results, then knowing the frequencies of these blades, and inferring their relative stiffness (at least to the point that blade a is stiffer than blade b, but less than blade c) is the best we have?
 
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Finally, Thank you!

Bounce tests won't cut it either unless you can shoot balls at the blade at various speeds.
...
This is what I meant in the beginning when I said that speed was more like a curve.

Excellent post, where the Butterly Innerforce ALC's are examples of this.

Cheers
L-zr
 
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Golf equipment is measured,
I think there is a maximum, speed / velocity that the sports regulators have set for the ball to leave the face of the club face when the ball is struck with a set force. I’m not 100% sure but I think they fire a ball at the club face at speed/velocity ‘a’ and measure the rebound speed/velocity which cannot be greater than their set speed/velocity of ‘b’
The set maximum values haven’t changed, but the pro’s still hit the ball further!! So what’s changed? Similarly to TT it’s the ball!! Manufacturers have spent loads of money on R&D of golf balls!! This has resulted in more yards gained than technical developments in clubs!!
Coaches and manufacturers recommend being ‘fitted’ for your clubs, there’s a change of thought regarding shaft flex, this is apparently not as important as once believed.

So there’s a set limit in place but all the clubs will feel different and perform differently for any given individual. THIS WILL BE THE SAME FOR TABLE TENNIS PLAYERS REGARDLESS OF WHAT VALUE IS GIVEN TO A BLADES ‘SPEED’ and is further compounded by the multitude of rubber and sponge combinations available.

The good news (for golfers) is they get to try before buying, a luxury TT players generally don’t have.

To ‘officially’ validate a figure for the speed of a blade, it would need to be regulated, this would need to come from the ITTF and would possibly involve a number of testing regimes. This just ain’t gonna happen!! But would definitely ease or remove ‘doubt’ issues buyers may have about a blades ‘speed’

Interestingly,

Golf has, to a certain extent restricted CLUB (which can be equated to the TT bat) performance, because back in the day this was seen as the aspect that would effect how far you could hit a ball! This resulted in manufacturers highlighting the ball as the equipment that can be best adapted because the rules regarding the ball were way more relaxed. This R&D has resulted in courses being seen as ‘easy’ because they are now too ‘short’!!
Golf are now considering regulating the ball !!!! ;);) You just gotta laugh!!

TT identified the BALL as the equipment that needed to change to ‘slow’ the game down!! Result - manufacturers spent money on rubber/sponge R&D, this led to faster, spinny rubber/sponge combinations which may have negated the ball changes !!

Lesson learnt - if you are going to change rules for equipment, DON’T FOCUS ON ONE PIECE OF EQUIPMENT regulate both club & ball for golf, or rubber/sponge/blade & ball for table tennis!!!
 
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You guys are changing the topic because you know you have embarrassed yourselves by clinging to using frequencies. Now it is not good energy to calculate the COR using the before and after impact speeds.

Well how do you propose to measure the speed of the blade AT DIFFERENT SPEEDS using frequencies?
The frequencies won't change as the speed of impact changes, only the amplitude which is something you guys ignore.

If could only read and UNDERSTAND the Tiefenbacher pdf! Teifenbacher computed the COR as a function of speed.

This is also a problem with the ITTF's specification for COR for TT balls. It only measures the COR by dropping from one height, 30 cm. As long as the TT balls meet the specification when dropped from 30 cm everything is good but all the ball's COR could be much different if dropped from different heights. This is what happens when you let people that don't know anything make up specifications.

Zeio is the one full of BS. Show us an equation for computer the COR of the blade as a function of frequency. You can't.
Zeio still hasn't explained reduced mass. Zeio posted a pdf on mytt about reduced mass applied to TT years ago. No one understood it but everyone thought it was good. It was a misapplication of reduced mass but it is hard to argue anything on a forum when no one understands what they are talking about.

The Tiefenbacher pdf talks about this very thing. Tiefenbacher mention TT mysticism making it hard to discus TT physics in the second paragraph of the first section.
 
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So when we bounce the ball on the blade, what we hear (and find the frequency with mobile) corresponds to the membrane vibration mode (the (0,2) mostly) of the blade, which in the ttgearlab terminology corresponds to the Ec (central elasticity index).

What we see is how the ball bounces, which we can't easily measure and compare, but that would be what we would call "speed" (ignoring for now that the response isn't linear on the drop-height). That happens to correspond (is not caused, just corresponds) with the stiffness (another word for elasticity), and in the ttgearlab terminology corresponds to the Ep (Primary Elasticity Index). And it more strongly correlates with the bending vibration mode (the (1,0), the fundamental), where the frequency is usually around 100-300Hz, and we could feel it in the handle more, because there the amplitude of it is biggest.

Normally when I bounce the ball on a blade, the merchant already has got a grin on his face and my money in his pocket.

Worse than that for me. Even if I bounce the ball on the blade, I still don't know whether I'll like the blade or not. I'll only know when I put rubbers and play with it. I know I dislike some blades, with high Ec close to Ep, but I can't find it reliably. The kick of the blade - can you recognize it by bouncing? I guess it takes a lot of experience.

Rereading was interesting, it would be great if zeio could post more about the in-plane bending.

The in-plane bending mode is another mode that's rarely discussed/measured, which is actually very prominent in serving/pushing/looping/chopping.

The Tiefenbacher document linked by brokenball is very approachable, good read, thanks. And also the 2nd document linked by langel, the PingPongAcoustic, thanks. And many thanks to hysteresis and hipnotic.
 
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