Vibration Frequency: New TWU Tool

[TW Professor]

We have a new racquet comparison tool for vibration frequency at:
http://twu.tennis-warehouse.com/cgi-bin/vibfrequency.cgi
or click "Vibration Frequency" on the "Racquet Comparisons" menu at Tennis Warehouse University.

Vibration frequency is a more precise way to measure racquet stiffness. Dynamic stiffness (i.e., impact vs static) depends on both material/construction stiffness and mass distribution. We impact the racquet at 25 inches and measure the vibration at 10 cm from the butt.

There is a longer explanation if you click the "information" link on the top of the page.

We have tested most of the newer racquets and will go backwards as time permits.

 

[jwbarrientos]

Interesting, Is it correct to say that a less vibration frequency is "more arm friendly"?

 

[drak]

Hey TW Pro, I had a question on the Volkl PB9's stats in your too about power levels at various points in the stringbed - they were quite a bit lower than the DNX9 and the close to the same as a very lower powered racket like the Gamma T7 - I now own the PB9 and can tell your from hands on experience that the stats listed in the tool are likely wrong. Please clarify or recheck when possible.

 

[Don't Let It Bounce]

Interesting, Is it correct to say that a less vibration frequency is "more arm friendly"?

Pretty much. But beware drawing the conclusion that therefore it is the higher frequencies that harm the elbow; that doesn't follow (though I have heard claims that higher frequencies can aggravate existing injuries). It's more like this: the racquets that vibrate at higher frequencies (i.e., stiff ones) are also the racquets that transmit more shock to the arm instead of absorbing it.

 

[TW Professor]

Interesting, Is it correct to say that a less vibration frequency is "more arm friendly"?

It may or may not. The question is whether it is the shock or the vibration that hurts the arm. You can't necessarily judge the amount of shock from the vibration frequency. We will be adding the shock force values to these numbers soon (I hope).

 

[vsbabolat]

10................

 

[samster]

We have a new racquet comparison tool for vibration frequency at:
http://twu.tennis-warehouse.com/cgi-bin/vibfrequency.cgi
or click "Vibration Frequency" on the "Racquet Comparisons" menu at Tennis Warehouse University.

Vibration frequency is a more precise way to measure racquet stiffness. Dynamic stiffness (i.e., impact vs static) depends on both material/construction stiffness and mass distribution. We impact the racquet at 25 inches and measure the vibration at 10 cm from the butt.

There is a longer explanation if you click the "information" link on the top of the page.

We have tested most of the newer racquets and will go backwards as time permits.

TW Professor,

Please include the Volkl Power Bridge 10 MID data, please?

 

[jwbarrientos]

It may or may not. The question is whether it is the shock or the vibration that hurts the arm. You can't necessarily judge the amount of shock from the vibration frequency. We will be adding the shock force values to these numbers soon (I hope).

:shock: Holy crap, you sound like me lecturing at University

So it is a non conclusive data without having more info, since this is a very interesting figure how could a regular human being find out what is a good vibrations?

It would be also usefull if this numbers could bring you some ideas to adopt dampeners.

 

[Bud]

TW Professor (Sweetspot on Power Maps)

Is it possible to place a faint dashed outline of a racquet's sweet spot location and size on the power maps?

For example... below are the power maps for the new APDGT... I'd love to see where the sweetspot is located in relation to the power map... and also its size.

Also... is it possible to automatically sort every TW racquet by twistweight?

 

[Don't Let It Bounce]

We have tested most of the newer racquets and will go backwards as time permits.

I read in Technical Tennis that if the racquet vibration frequency is high enough, ~200 Hz, the first vibration is completed before the ball even leaves the strings, so the ball itself dampens a great deal of vibration (reducing its amplitude and duration). My understanding from other readings is that this was Kuebler's goal in designing the racquet that eventually became the Wilson Profile.

So, when you get to the old time racquets, I'd be especially interested in the very stiffest ones, the ones that might cross that 200 Hz threshold: Profiles, Hammers, Secrets, etc. (I'm assuming there aren't any current frames that stiff, but that's just an assumption.)

In the meantime, if I'm wrong about any of the above, I'd welcome being set straight.

 

[corners]

TW Professor,

Please include the Volkl Power Bridge 10 MID data, please?

Yes please, another request for testing of Volkl Powerbridge10 MID!

 

[corners]

Is it possible to place a faint dashed outline of a racquet's sweet spot location and size on the power maps?

For example... below are the power maps for the new APDGT... I'd love to see where the sweetspot is located in relation to the power map... and also its size.

Also... is it possible to automatically sort every TW racquet by twistweight?

Hey Bud,

I'm pretty sure the sweet spot you're referring to is the center of percussion (COP). The COP has no size as it is a true 'point'. You can find the COP with this equation: COP (cm from butt) = SW/(R*M)

Where R = balance in cm minus 10 and
M = mass in kg

I think that the "power zone" maps are the only real way to quantify the size of the 'sweet spot' that most of us talk about when we assign it a size and location.

 

[jrod]

Yes please, another request for testing of Volkl Powerbridge10 MID!

Yep, me too!

 

[Bud]

Hey Bud,

I'm pretty sure the sweet spot you're referring to is the center of percussion (COP). The COP has no size as it is a true 'point'. You can find the COP with this equation: COP (cm from butt) = SW/(R*M)

Where R = balance in cm minus 10 and
M = mass in kg

I think that the "power zone" maps are the only real way to quantify the size of the 'sweet spot' that most of us talk about when we assign it a size and location.

I was hoping they could locate it for quick reference then interpolate its size, based on the power map data, twistweight, etc... perhaps, I'm asking for too much

 

[vkartikv]

I wonder where else such a tool could be used

 

[samster]

Where are you, TW Professor?

 

[Bud]

Where are you, TW Professor?

He went AWOL :shock:

I wonder where else such a tool could be used

What did you have in mind?

 

[sureshs]

I wonder where else such a tool could be used

You have a dirty mind, Kramer

 

[eagle]

Yes, please include info about the effects if any of "vibration" dampeners.

Maybe you can put to rest the debate over whether these innocuous things do anything at all outside of deadening the sound. If they do anything beneficial and significant, then maybe they do deserve their name. If not, then they should simply be called sound dampener instead.

r,
eagle

 

[klementine]

I wonder where else such a tool could be used

Some PG rated suggestions...

-Cutlery
-Drumheads and drumsticks
-Axes
-Japanese Swords
-Police Batons
-Baseball or Cricket Bats


... wait that's not all... call within the next half hour and we'll test the frequency of....

-swedish refrigerator doors
-umbrellas
-My Pet Montser
-Slap bracelets
-Fly swatters
and.....
-big wheels !!!! That's right big wheels for adults !!!!!

 

[Anton]

Request for Prince EXO Rebel 95 test!

 

[Bud]

Request for Prince EXO Rebel 95 test!

Request denied! :twisted:

(j/k... it ain't up to me)

 

[Bud]

TW Professor?

Is he back from vacation yet?

 

[TW Professor]

TW Professor,

Please include the Volkl Power Bridge 10 MID data, please?

Coming soon. Had it strung up but it ended up to be the MP. Will try again.

 

[jrod]

Coming soon. Had it strung up but it ended up to be the MP. Will try again.

Hurry!!! Many a poster anxiously awaiting the numbers....

 

[samster]

TW Professor,

Please include the Volkl Power Bridge 10 MID data, please?

Coming soon. Had it strung up but it ended up to be the MP. Will try again.

Thank you, TW Professor!

 

[TW Professor]

I read in Technical Tennis that if the racquet vibration frequency is high enough, ~200 Hz, the first vibration is completed before the ball even leaves the strings, so the ball itself dampens a great deal of vibration (reducing its amplitude and duration). My understanding from other readings is that this was Kuebler's goal in designing the racquet that eventually became the Wilson Profile.

So, when you get to the old time racquets, I'd be especially interested in the very stiffest ones, the ones that might cross that 200 Hz threshold: Profiles, Hammers, Secrets, etc. (I'm assuming there aren't any current frames that stiff, but that's just an assumption.)

In the meantime, if I'm wrong about any of the above, I'd welcome being set straight.

We often make statements like racquets that tend to be stiff also tend to be lightweight. I wondered if this were really true. Below are some interesting graphs:

As you can see there is actually no trend of RDC flex vs weight or swingweight. However, we do know that very stiff and very light frames will deliver more shock. That is what we remember. Then I guess we make the "trend" in our head as if it were a general rule of racquets, which it obviously is not. You can make both light and heavy racquets any stiffness you want.

Frequency depends both on stiffness and weight and you can have almost any combination of these two also. However, there is a weak trend of frequency to go down as weight goes up. That is as it should be. If you have an infinitely flexible material but it is also infinitely heavy, it still has a zero frequency--i.e., it just isn't going to move in any way shape or form.

And there is a much stronger trend between material stiffness (flex) and frequency, as you can see. So frequency depends on both weight and material stiffness and you can have many combinations of those. And it is the frequency that you will feel as the "softness" or "stiffness" during an impact. That is a feel issue. That is what we are relating to while hitting.

Shock is more generally pointed to as the culprit in injury. Light and stiff will be the ingredients for the most shock (the upper left hand corner of the flex vs weight graph.

As you indicate, frequencies that are very high (200 Hz) will be dampened by the ball while it is still on the strings.

So frequency is most often about what you like the feel to be. It is probably not so much about injury. That's why the frequency numbers are so interesting--it better allows you to focus in and identify one of the determining factors in the "feel" that you like.

 

[TW Professor]

Oopps. I have the graph titles reversed. It should read Flex vs Weight, Flex vs Swingweight, and Frequency vs Weight.

 

[jrod]

....

These two plots are very nice indeed. Really nice work!

 

[drak]

Oopps. I have the graph titles reversed. It should read Flex vs Weight, Flex vs Swingweight, and Frequency vs Weight.

Hey Mr Professor you were supposed to recheck the stats on the PB9, they look incorrect in the racket comparisons.

 

[TW Professor]

Hey Mr Professor you were supposed to recheck the stats on the PB9, they look incorrect in the racket comparisons.

You are right. The data at 19/0 and 21/0 was mistyped. It brings up the power some. Thanks.

 

[Bud]

TW Professor?

Is it possible to place a faint dashed outline of a racquet's sweet spot location and size on the power maps?

For example... below are the power maps for the new APDGT... I'd love to see where the sweetspot is located in relation to the power map... and also its size.

Also... is it possible to automatically sort every TW racquet by twistweight?

Hey Bud,

I'm pretty sure the sweet spot you're referring to is the center of percussion (COP). The COP has no size as it is a true 'point'. You can find the COP with this equation: COP (cm from butt) = SW/(R*M)

Where R = balance in cm minus 10 and
M = mass in kg

I think that the "power zone" maps are the only real way to quantify the size of the 'sweet spot' that most of us talk about when we assign it a size and location.

I was hoping they could locate it for quick reference then interpolate its size, based on the power map data, twistweight, etc... perhaps, I'm asking for too much

Any possibility of this?

 

[CanadianChic]

Interesting, Is it correct to say that a less vibration frequency is "more arm friendly"?

Ahhh. Working on my restraint is an ongoing battle. :twisted:

 

[TW Professor]

Is it possible to place a faint dashed outline of a racquet's sweet spot location and size on the power maps?

For example... below are the power maps for the new APDGT... I'd love to see where the sweetspot is located in relation to the power map... and also its size.

Also... is it possible to automatically sort every TW racquet by twistweight?

The sweetspot is just a spot. Whether it is the no shock or no vibration spot, both are usually just below the center of the racquet face. The power zone maps are derived from the location maps. The combination of the two qives you a quantity and quality look at the racquet face. On the power zone maps, the light gray dots show the test impact points used in determining the zone map. The current procedure for producing these doesn't make it easy to add anything else to the maps at this time. Maybe somewhere else. We'll see.

Right now you cannot sort by twistweight anywhere on TWU. In fact, you can't really manually sort all racquets by anything. That is a short coming I will get to sooner or later.

 

[Bud]

The sweetspot is just a spot. Whether it is the no shock or no vibration spot, both are usually just below the center of the racquet face. The power zone maps are derived from the location maps. The combination of the two qives you a quantity and quality look at the racquet face. On the power zone maps, the light gray dots show the test impact points used in determining the zone map. The current procedure for producing these doesn't make it easy to add anything else to the maps at this time. Maybe somewhere else. We'll see.

Right now you cannot sort by twistweight anywhere on TWU. In fact, you can't really manually sort all racquets by anything. That is a short coming I will get to sooner or later.

Thanks TWP... I'm aware that literally the SS or COP is just a single point.

Perhaps a more appropriate term would be 'sweet zone' as we've all felt racquets where that zone is tiny (PS85) and some where it seems much larger KPS88. I think much of that zone size has to do with twistweight. It seems that the more stable the racquet (i.e. high TW), the bigger that zone of higher stability/low vibration, etc.

It appears that people often refer to this sweet zone as the sweet spot... and I thought with all the info now available for the racquet... this zone could be approximated.

 

[TW Professor]

Thanks TWP... I'm aware that literally the SS or COP is just a single point.

Perhaps a more appropriate term would be 'sweet zone' as we've all felt racquets where that zone is tiny (PS85) and some where it seems much larger KPS88. I think much of that zone size has to do with twistweight. It seems that the more stable the racquet (i.e. high TW), the bigger that zone of higher stability/low vibration, etc.

It appears that people often refer to this sweet zone as the sweet spot... and I thought with all the info now available for the racquet... this zone could be approximated.

That is the intent, anyway, of the zone maps. Though they maps of power, they are also maps of "sweetness." That is so in the respect that more power is the end product of less vibration, less rotation, less twisting, less translation. These things are not "sweet," and as such, the zones of higher power are also zones of sweetness.

That being said, you can have the same power with different combinations of those ingredients. So two racquets with a power potential of 42% at the center, for example, can still feel different in the sweetness department. But still, if you know the area you hit on your racquet, you can at least make a good guess at how one racquet will feel compared to another by looking at the zone and location maps and comparing the data at your desired impact location.

 

[Don't Let It Bounce]

How are these tests conducted? (Oscilloscope? Computer-based audio frequency monitor? If so, what is the procedure for producing the vibration to be measured?) Could someone with a good ear get a rough approximation of the relative frequencies of two racquets by suspending a frame (so one's hand doesn't damp the sound), tapping it, and comparing the pitches?

I hope someday frequency ratings will become part of a standard spec for racquets. In the meantime, as the to-do lists of TWP and other TW folk get longer and priorities are re-examined, let me cast a vote here for building on the list you've already started. It's a worthwhile project.

 

[corners]

How are these tests conducted? (Oscilloscope? Computer-based audio frequency monitor? If so, what is the procedure for producing the vibration to be measured?) Could someone with a good ear get a rough approximation of the relative frequencies of two racquets by suspending a frame (so one's hand doesn't damp the sound), tapping it, and comparing the pitches?

I hope someday frequency ratings will become part of a standard spec for racquets. In the meantime, as the to-do lists of TWP and other TW folk get longer and priorities are re-examined, let me cast a vote here for building on the list you've already started. It's a worthwhile project.

This is an old thread, but just wanted to note that manufacturers do print the vibration frequency on blacked out prototype frames. This is clearly a very important spec - the feel spec. For those who haven't checked out the vibration frequency database: http://twu.tennis-warehouse.com/cgi-bin/vibfrequency.cgi

 

[Hi I'm Ray]

Good stuff, very interesting. Thanks TW & the Prof. for this, and corners for digging it up. I didn't know this info was even available. I think all these TW threads should be sticky.

This does confirm what I've noticed and backs up what I've posted before: Stiffness ratings can be misleading and don't always tell the whole story regarding harshness/comfort in actual use. I can play with a APDGT but find a PDGT too harsh, & the PDR 2012 was more comfortable than expected, APDGT + feels flexier than APDGT, BB DC Pro is quite comfy for a power frame, Yonex V-Core felt harsher than expected, Donnay Pro One is more comfortable than PDR 2012 (and APDGT)Dunlop 500 Tour felt quite stiff (well only the Bio 500 T is in the database, but if they are similar enough)

Racket - Stiffness Rating - Vibration Frequency:

BB DC Pro - 69 -153
APDGT + - 70 - 155
Donnay Pro One - 69 - 156
APDGT - 70 - 160
PDR 2012 - 72 - 163
Yonex V-Core 100s - 72 - 164
Dunlop 500 Tour - 72 - 166
PDGT - 72 - 168

 

[corners]

Good stuff, very interesting. Thanks TW & the Prof. for this, and corners for digging it up. I didn't know this info was even available. I think all these TW threads should be sticky.

This does confirm what I've noticed and backs up what I've posted before: Stiffness ratings can be misleading and don't always tell the whole story regarding harshness/comfort in actual use. I can play with a APDGT but find a PDGT too harsh, & the PDR 2012 was more comfortable than expected, APDGT + feels flexier than APDGT, BB DC Pro is quite comfy for a power frame, Yonex V-Core felt harsher than expected, Donnay Pro One is more comfortable than PDR 2012 (and APDGT)Dunlop 500 Tour felt quite stiff (well only the Bio 500 T is in the database, but if they are similar enough)

Racket - Stiffness Rating - Vibration Frequency:

BB DC Pro - 69 -153
APDGT + - 70 - 155
Donnay Pro One - 69 - 156
APDGT - 70 - 160
PDR 2012 - 72 - 163
Yonex V-Core 100s - 72 - 164
Dunlop 500 Tour - 72 - 166
PDGT - 72 - 168

I agree that the Professor's posts should be stickied. They tend to get buried and forgotten and many times they would answer the types of questions that are asked repeatedly on this racquet forum.

From looking at the data, and the Professor's graph of RDC flex vs. vibration frequency, it's clear that the flex rating does closely correlate with the frequency measurement, but that weight (and weight distribution) also factors in. I think one thing to keep in mind is that we talk about racquets in terms of how "soft" they feel. But "soft" is not a word that relates directly to stiffness. The opposite of stiff is flexible, not soft. I think the same thing happens when discussing strings: people say that this string or that feels "softer" than the stiffness data for that string would indicate. But again, a stiffness measurement is not a measurement of softness or hardness, but of relative stiffness or flexibility. The sensation of softness may only partially come from low flex or low vibration frequency. Vibration damping technologies - foam cores, siliconed handles, etc. - probably also come into play in a way that isn't reflected completely in the data. There is a section in one of the Professor's books where he and his co-authors talk about racquet feel as a combination of shock and vibration. Vibration follows so quickly after the initial shock that it's likely that our hands and brains can't clearly distinguish between them. Stiff racquets transmit greater shock but less vibration, and flexible racquets transmit less shock but more vibration. So it's easy to see how a bit less vibration in this racquet might make it feel "softer" than that racquet if they both share the same approximate stiffness. But I'm just guessing.

Anyway, the more data the better! But we still have to demo.