Expressing relative blade speed

Some theory of blade mechanics with some great illustrative images are in this thread
http://mytabletennis.net/forum/forum_posts.asp?TID=60725

Where's John Staley, aka JRSDallas? We miss you!
I wonder whether he further elaborated on/published his theory.










More recent scientific articles exploring the relationship between blade mechanics and acoustics
http://www.sciencedirect.com/science/article/pii/S1877705814005840
http://www.sciencedirect.com/science/article/pii/S1877705812017316


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Edited by arg0 - 10/27/2017 at 4:03pm

zeio wrote: As the mode goes higher, the role it has in the racket-ball interaction diminishes. Looking at the data, it looks like the mic is picking up the membrane mode the most, which contributes the most to the sound of the blade.

Yes, the highest peak in the audio spectrum is typically the frequency of the membrane mode.
Sound amplitudes at lower frequencies are normally deadened by the hand holding the blade.

Re: Magic_M's concerns:

I've also added arg0's list to the sheet

IMHO certainly better than anything we have had before. Especially given that the apps are free.

Congratulations to those of you who independently came up with this.


One thing that occurs to me to add.  I have about nine or so Viscarias, but one is amazingly better than all the others to play with.  It is the best blade I have ever played with and I am really lucky to have it (I bought it here by the way).  It is not just the weight, and it is not just the pitch when I knock it against my head.  I have a couple of other blades that are similar in terms of weight and pitch (although a lot of them have a higher pitch and don't feel anywhere close to as good).  Somehow this blade's sound seems to be a lot more "pure" and seems to resonate longer.  Next time I change the rubber I will get this app and compare it to some of its lesser brethren to see if some difference shows up in its spectrum (I expect this would show up in the higher components of the spectrum).  Might be awhile though, the rubber that is on it refuses to die and is playing great right now, so I don't want to mess with anything. It may depend a lot on how good the pickups are in my phone. 

At some point I predict people will be providing this number for blades they sell here.

I think this will be really useful for comparisons within a blade class-- comparisons of one all wood to another, or comparing two different ALC/ZLC blades.

Zeio is right to remind us that how or if the blade is secured will potentially affect tbe result.

zeio wrote: Other than the speed, the mode of vibration can reveal a lot about a blade. The 1st bending mode is usually within the first few hundred Hz, lower for a clamped blade, and higher for a freely-suspended blade, with the real-world grip resembling the latter, but with higher damping. The 1st torsional mode follows closely. The 2nd bending mode comes next, and so on. The membrane mode doesn't come in until much later. The 1st bending mode contributes the most to dwell/feel as the handle vibrates the most at that frequency. That mode is also related to the sweet spot as one node(least vibration) is somewhere in the upper center of the blade head and another node where the handle meets the blade head. The 1st torsional mode gets agitated the most when the racket is hit off-centered. As the mode goes higher, the role it has in the racket-ball interaction diminishes. Looking at the data, it looks like the mic is picking up the membrane mode the most, which contributes the most to the sound of the blade.

Edited by BigFatLoop - 06/30/2017 at 8:56pm

arg0 wrote: berndt_mann wrote: I still retain some knowledge about music theory, though its been 50 years since I last studied music theory at the Cleveland, Ohio Institute of Music.  It never occurred to me, however, or any other table tennis player I knew to try to measure the amplitude or frequency peaks of any of the blades I used while also studying classical defensive table tennis theory under six-time Ohio State Champion and two-time National Doubles Champion Danny Vegh. I suspect recording and spectrum analysis equipment was less readily available, then. Studying mechanical response of the blades is interesting to some. Does it make you a better player? No. Does it give you at least one objective criterion to assess blade characteristics? Yes.

Including the range of mechanical responsex seen for different samples of a particular type of blade.

slevin wrote: I suggest putting down your blade weight (if you know it). A 80g Viscaria shall show different readings than a 92g Viscaria. Donic Ovtcharov True Carbon (88g): 1571 Butterfly Marcos Freitas ALC (87g): 1464

It's not just weight though. I have two Viscaias of the same weight that have a different tone when I knock them against my head, and it would certainly show up on this measurement. And yes, the one with a higher pitched tone is faster

berndt_mann wrote: I still retain some knowledge about music theory, though its been 50 years since I last studied music theory at the Cleveland, Ohio Institute of Music.  It never occurred to me, however, or any other table tennis player I knew to try to measure the amplitude or frequency peaks of any of the blades I used while also studying classical defensive table tennis theory under six-time Ohio State Champion and two-time National Doubles Champion Danny Vegh.

I suspect recording and spectrum analysis equipment was less readily available, then.

Studying mechanical response of the blades is interesting to some. Does it make you a better player? No. Does it give you at least one objective criterion to assess blade characteristics? Yes.

For a related discussion, see this thread.

Donic Ovtcharov True Carbon (88g): 1571

haggisv wrote: Interesting idea... I can't see it working for all blades though. For example balsa blades can be very slow on low impact, yet very fast at higher impact.  It might work for the more standard blades though. Where is the iphone app?

zeio wrote: qpskfec wrote: I would like to see results from testing both sides of a combo blade. A combo blade being one with an asymmetric design - different composition on each side, typically made for people to use inverted rubber on one side and LP on the other. If one side is much softer wood than the other, are the frequencies the same? Frequencies should be the same, but the amplitude could be different on either side.

A combo blade is made so that the ball reacts differently depending on which side you use. The frequency is the same for both sides but the ball reacts differently for both sides. This tells me that knowing the frequency doesn't tell me which side is faster and may or may not be a very interesting fact to know.

Coefficient of restitution is much more interesting than frequency. That is why golf club designers measure COR to get the COR up to the legal limit. My guess in tt blades is that COR will vary depending on swing speed due to multiple layers of different materials.

Golf club designers measure frequency and tune the frequency. They do not try to maximize frequency for performance, it is done to make the golf club more pleasing to the ear.

Interesting idea... I can't see it working for all blades though. For example balsa blades can be very slow on low impact, yet very fast at higher impact.