Manufacturer's myths. Paddle Palace's article on sponge hardness.

[brokenball]

In the Paddle Palace catalog #307, on page 66, there is an article that was cobbled together with input from so called Andro and Tibhar experts. These "experts" are clearly just marketing people, not experts.
The article is about choosing the correct sponge hardness. There are 5 questions.
1. "why does sponge hardness matter?"
2. "What is the difference in performance from a rubber that has a soft sponge, medium sponge, or a hard sponge?"
3. "Why would I, as a player, choose a harder or softer sponge?"
4. "What is the most important consideration for which kind of rubber I should use?"
5. "How should my choice of sponge hardness be affected by my style of play, how far back I stand from the table, what type of rubber I use (smooth, short pips, longpips), and my level of expertise, or other factors?"

The answers are long but the over all theme is that soft sponges are for beginners and hard sponges are for experts. The answer attributed features like speed, spin and control to the hardness of the rubber. This is nonsense. Speed and spin is a function of the rubbers elasticity. There can be hard dead rubbers or soft dead rubbers. These types of sponges are on anti rubbers. There can be springy hard and soft rubbers too.

We all know that the hardness is measured in durometers. Although it is easy to find how much force it takes to make an indentation, there is no measure of elasticity or how long it takes for the rubber to spring back to the original shape after the indenting force is removed. Hardness or softness cannot be directly equated to springiness. This is fact.

I think the "experts" need to go back an read the story about Goldilocks and the Three Bears. Some rubbers will be too soft and may even "bottom out" and some rubbers will be too hard ( Why don't the pros use SST Pro Team, it is very hard. Why do they want to make the hard rubbers softer by boosting? ). Most of us are like Goldilocks. We want a rubber that is not to hard and not too soft, but just right.

So overall I would forget what the so called "experts" have to say. Get what works for you.

Now for the geek speak.

Harder rubbers absorb less energy than soft rubbers. If they absorb less energy then they will return less energy If you look at a cm^2 of rubber as a spring you will see the amount of energy absorbed is roughly proportional the distance the rubber is compressed squared. E = k*Δx^2. Harder rubbers will have a higher value for the spring constant k but lower values for compression distance Δx. When the rubber decompresses the rubber will push the ball back most of that compression distance. That fraction of the compression distance, where the rubber is still pushing the ball, divided by the time is the extra speed or trampoline affect that gets added to the paddle speed.

Something that must be considered it that the ball must accelerate the mass of the top sheet and sponge between the ball and sponge. When the rubber springs back it must accelerate not only the ball but also the mass of the compressed sponge. The energy that is required to accelerate the sponge is lost. So there is a trade off between hard and soft rubbers. Harder rubbers will not compress much so the trampoline effect will be small. Soft rubbers may not spring back fast enough to keep up with the ball so again a lot of the trampoline effect is lost. There is a happy medium but it will not be the same for every body and for every condition.

What is interesting is that people talk about dwell time of the rubber and seem to blindly state they want more dwell time. If the time it takes the rubber to spring back is longer then the trampoline effect is reduced. Again, there is a Goldilocks zone.

It should be clear I don't see this as a hard vs soft issue but more of a what is just right for you issue.

 

[Suga D]

Is the catalogue online and could you post a link or take a photo.
Did they write their names?
There are a few former German top players now working for Andro. Some in R&D, some Marketing, the managing Director (i think you guys call his position CEO) is former German National Team player Ralf Wosik, so it wouldn't be too farfetched to call either of them an expert.

[Edit: just opened it as PDF file. Too bad unfortunately there ain't no namedroppin'.]

 

[Badger]

@brokenball
What are your thoughts on the accompanying article on page 80 of the same catalog?

 

[langel]

The coaching corner of Samson makes it clear, and it coveres with a lot of the discussions here.

 

[Der_Echte]

BB is basically saying that in the world of "Result of Impact" there are more considerations than just sponge hardness.

He lists a couple and presents some simplified calculations to support his ideas exhorting people to not be suckered by a sponge softness description.

I believe he is right in saying "There is more to it" "Don't be duped"

However, I believe there are even MOAR variables that go into the impact to produce a result. Many of them are difficult to measure, quantify, and provide exact relationships.

Elasticity of the rubber at different force level encounters is an important one BB touched upon.

Some other important variable factors are:

1) How the rubber was glued to the bat (Any old timers remember the "horror" of a bad glue job?)
2) How the topsheet is attached to the sponge
3) The pip structure
4) The thickness of topsheet
5) The player's grip pressure dynamics at and during impact

I like BB's Goldilocks analogy. Doting on hat one, I have a mattress that is rated super soft... I am 100 KG so it shouldn't work, but it does, just perfect. There is more to it than just softness. My first couple inches are super soft, next level is medium, bottom layer is firmer. I sink into mid zone, top layer wraps me, mid layer floats me, bottom layer supports me.

I agree that the firm modern mattresses are a Goldilocks vomit story. I have a $3000 modern firm one and hate on it, while little ole lady just luvs it a lot. Go figure.

 

[langel]

Generally the softer sponge may have more trampoline with weaker balls, and at some point with faster acceleration it will lose it. The opposite - a harder sponge generally will feel dead with sogter touch, but may give a much stronger catapult with heavy hits. Its the same as with the spiral metal springs - a soft one will spring a lighter object, but will die when pressed with a heavy one, the a harder spring will stay immaculate with lighter object, but will shoot off a heavier.
The mattress story of Der_Echte remind me that there are some multilayer rubbers /japanese I think/ which have a softer upper sponge layer and a harder layer under it.
Of course there are many rubbers with mixed characteristics, and besides that everything depends on many other factors.

 

[Badger]

The coaching corner of Samson makes it clear, and it coveres with a lot of the discussions here.

The article on page 80 essentially echoes the advice presented on page 66-67.

 

[genrel001]

A graph would be very helpful and easier to understand. Say, a graph between trampoline effect and hardness of the rubber with impact force being constant. Thank you.

 

[igorponger]

Durometer with Shore A scale is a must-have to verify the numbers you see imprinted on the sponge's backside or on rubber envelopes. Don't take the numbers as granted. Check it up, always.

Be happy.

 

[brokenball]

@SugaD. There is no by-line for the article on page 66. The article just said it came from Andro and Tibhar experts.

@Badger, i agree with Dubina's opening paragraphs about how the angle of contact determines the ratio of spin to speed. However at that point Dubina has said nothing about the hardness of rubber. Dubina does seem to echo the article on page 66. While I agree that starting out beginners with a soft sponge is good, it is only because beginners do not play far away from the table. The high arcs or slow loops are easy with Reflectoid. Dubina then goes on to say this medium rubbers to this and hard rubbers do that. He doesn't address why and I think why is import to understanding what is right for you. I think it is wrong to say soft rubbers make high arcs. This implies it can't be done with harder rubbers. What makes a high arc? Why do we even want high arcs? Do the pros hit high arcs? No!

What makes a ball move on its trajectory is called an impulse. This is the integral of force over the contact time or dwell time.
Harder rubbers will have shorter contact or dwell times but the force during that time can be higher so the same impulse can be achieved with a hard rubber as with a soft rubber. Obviously pros must be able to make high arcs if necessary. What Dubina said in the first paragraph is exactly how the pros can make these high arc shots if they want too. It is a matter of trading off speed for spin. With harder rubbers a high arc is achieved by brushing the ball more so there is less speed and more spin.
Obviously a beginner will not have the fine timing necessary to achieve this hard rubber so that is why we agree a beginner should start out with softer rubber but it is wrong to imply that the only way to achieve slow high arc loops is with soft rubber.

@Der_Echte, I don't think I mentioned anything about the elasticity or coefficient of restitution this time. You have a good memory because I have said it before. It is nice to know someone is listening and remembers. However, it is true that elasticity drops almost linearly with impact speed. What is a shame is that I have seen no modern research on this with the plastic balls.
[Detour] There is a specification for how high a ball must bounce off a steal plate from a distance of 30cm I believe. I haven't seen where this specification has changed from celluloid to plastic balls. However, what if the ball bounces from 20cm or 100 cm. Will the plastic balls bounce the fraction of the drop height as the celluloid balls? I think this question has been over lookedl
[/Detour]
While I agree there are many things that can affect the elasticity or coefficient of restitution, only the coefficient of restitution and the mass of the ball and the paddle/hand are used in the the speed after impact formulas. There is no equation for calculating the speed after impact using durometer or hardness readings. There can be fast and slow hard rubbers and fast and slow soft rubbers. The same goes for spin. It is still a optimization problem and the optimal solution will be somewhere between vary soft and very hard. After all who do you know that plays with very soft rubber or very hard rubbers like SST Pro Team God Favored ( very hard but not that fast).

@langel, what you are saying is that softer sponge will "bottom out" where harder sponges will not. That is why I don't buy 1.5mm soft sponges. I have few problems with 1.8mm and had no problem with 2mm+ thick soft sponges.

@genrel001. I like graphs too. I think about it. I have other priorities that pay real money.

 

[langel]

The general properties of the sponges are just what they are. The article of Dubina explains them shortly, because its a magazine, not a scientific paper, and the article is addressed more to the beginners.
But here I think there is a little mess between pure sponge's properties and "rubber" properties, where "rubber" is a rubber top sheet plus a sponge, and players style and expertise.
No one playes with a pure sponge. We play with a bat, which is a system, the properties of a bat depend on every element if the system and on the way these elements interact, their synergy or the lack of it. Its very difficult to build a system with a perfect synergy between its elements and this system to be in perfect synergy with the player. Thats what we call "dream setup". But to start to build a system, or to improve an existing one, we have to pay attention to the pure properties of every element and to think how we can expect it to interact with the other elements. And all this thought with our own way of play in mind.

 

[zeio]

Dubina has the characteristics of soft and hard sponges mixed up. It should be the other way around. Hard sponges produce a higher and longer trajectory and vice versa.

 

[brokenball]

There seems to be a difference in opinion between Dubina and Zeio. This is the problem with TT forums. They have too much opinion and little facts. I said above that I would like Dubina to say why he thinks the way he does. I would like to know why Zeio thinks the opposite.

It would be good if Zeio or Dubina could point to an equation that proves their point but I know there are no equations for determining the path of the ball using the hardness of the rubber. There are equations that use elasticity or coefficient of restitution. There must be more than opinion.

I know there is a wide range of rubbers that can generate the same impulse to generate the same trajectory. The stroke may be a little different from rubber to rubber but the same result can be achieve with the skill of the player. People are very adaptable.

Now for an opinion.
I think there are way too much talk about changing equipment. The Paddle Palace catalog is getting to be very big. There are probably a 20-50 rubbers in everybody's Goldilocks zone that will be just right. The same goes for blades.

I like this
"I have a trajectory in mind"

 

[langel]

The articles are about the sponge hardness, not rubber hardness.
And speaking of rubber hardness, clarify what you mean - top sheet rubber, or the rubber as a ready article of top sheet + sponge, or just the sponge maybe.
There are many brands that make rubbers with one and the same sponge, but with different top sheet rubbers.
Articles with one and the same top sheet and different sponges are available too.
Sponges with one and the same hardness, but with different pore size and structure will have different peculiarities but overall same general features.
Rubbers may be thin or thick, hard or soft, with a lot of different kind of pimple architecture, different surface grip and tackiness etc. etc.
So every particular system of a top sheet rubber and a sponge will have its peculiarities.
But - the general phisical properties of an element, a sponge in that case, are just what they are, always.
And Dubina is right.

 

[zeio]

Equation?

Perhaps due to the nature of his line of work, our adorable engineer is still very keen on observing reality through mathematical models instead of empirical evidence. I guess that explains why his physical representation of the loop stroke is different from what normal people would typically expect.

Anyway, here is the empirical evidence.

Before our warriors turn to their keyboards, I should tell you up front it's not pure marketing. Butterfly has real experimental data to back it up, the usual normal and tangential CORs, initial and final linear velocities and angular velocities etc. I have a video that shows how they test a setup by shooting balls at it in the lab.

 

[Suga D]

Generally Zeio has a point, but (with a capital b) I think the general idea behind recommending softer sponges is that especially (most) beginners have a hard time engaging the sponge while looping with too hard sponges.
So when they use a sponge too hard for them they tend to flat hit instead of learning to spin the ball properly. For most beginners a soft sponge makes it much easier to engage the sponge while looping.
An experienced player shouldn't really have this problem, and can engage the benefits of harder sponges much easier than a beginner who learns how to swing and how to make the contact that results in spin.

I hope this has been somewhat understandable.

 

[langel]

The Fx versions are with softer sponge, giving more impulse then the sponge of the regular versions, but this additional impulse is working to some level of the impact strength - I've tested it, you don't believe - test it yourself. For me, the engineer, things fit. Nothing different from what I've said.

I've posted this many times, will do it again:

https://en.butterflymag.com/2015/06/all-about-tenergy-22/

 

[TTHopeful]

I find Hurricane 3 or hard based rubbers from DHS is good for beginners how is this possible as its very hard?