Measuring vibration frequency

A piezo (contact microphone)?

Edit:
Just tried it with a clip on piezo mic at 3 o’clock routed to my iPhone with the iStroboSoft tuner app and got it to register 129 Hz compared to the TWU 127 Hz when I strike the string bed. It also only flashes 129 really quick before jumping up to 478 Hz which is where the strings are vibrating.

If I move the clip to just above the grip and tap the top of the frame I get 149 Hz. If I hit the string bed again it goes to 145 Hz.

I’m tapping with the handle end of my alpha starting clamp.
 
Last edited:
ChanterRacquet said:
A piezo (contact microphone)?

Edit:
Just tried it with a clip on piezo mic at 3 o’clock routed to my iPhone with the iStroboSoft tuner app and got it to register 129 Hz compared to the TWU 127 Hz when I strike the string bed. It also only flashes 129 really quick before jumping up to 478 Hz which is where the strings are vibrating.

If I move the clip to just above the grip and tap the top of the frame I get 149 Hz. If I hit the string bed again it goes to 145 Hz.

I’m tapping with the handle end of my alpha starting clamp.
Click to expand...
Interesting! Are you holding the racquet in hand while tapping? Wondering what would happen if you used a string dampener to suppress the signal from string vibration.
 
This has been a fun, distracting experiment.

I was done with the strings in the aforementioned Blade 104 v7 so I cut them out to remove the string vibration from the signal.

Using the piezo, I get a reliable 136 Hz. But I also get 136 Hz just tapping the frame (without strings) so I bet that’s all they’re doing. You just need something that reports the frequency it hears. Problem with most musical instrument tuners is they don’t sample fast enough for how quickly the sound a racket makes dissipates.
 
PistolPete23 said:
Interesting! Are you holding the racquet in hand while tapping? Wondering what would happen if you used a string dampener to suppress the signal from string vibration.
Click to expand...
I grabbed my wife’s Blade 104 v7 to compare as she uses dampeners and yes, they sufficiently suppress the string vibration to get a clear reading, though I’m having to use the piezo. I’m getting 128 Hz on one and 125 Hz on the other.
 
Even if they are not very accurate, but are consistent, you'll at least have a way of comparing rackets. It might be interesting to see string vibration too, although there may be too many other variables to even get consistency. Maybe not though.
 
Steve Huff said:
Even if they are not very accurate, but are consistent, you'll at least have a way of comparing rackets. It might be interesting to see string vibration too, although there may be too many other variables to even get consistency. Maybe not though.
Click to expand...
The frequency of the strings is what the RacquetTune app uses, guaranteed. It just has a string/fudge factor to convert to overall tension.

I have just recently been measuring individual main tensions to see if I can just restring NXT crosses on my wife’s Blades when the NXT mains are barely notched but the crosses are gone in 3 hours. TBD

Interestingly enough, between two of my daughter’s Blades, there was more frequency drop on the slightly tighter string job. Weird or no, I wonder.
 
ChanterRacquet said:
I grabbed my wife’s Blade 104 v7 to compare as she uses dampeners and yes, they sufficiently suppress the string vibration to get a clear reading, though I’m having to use the piezo. I’m getting 128 Hz on one and 125 Hz on the other.
Click to expand...
Which piezo contact microphone do you have? I tried looking for one that could connect to the iPhone but didn’t find any.
 
ChanterRacquet said:
The frequency of the strings is what the RacquetTune app uses, guaranteed. It just has a string/fudge factor to convert to overall tension.

I have just recently been measuring individual main tensions to see if I can just restring NXT crosses on my wife’s Blades when the NXT mains are barely notched but the crosses are gone in 3 hours. TBD

Interestingly enough, between two of my daughter’s Blades, there was more frequency drop on the slightly tighter string job. Weird or no, I wonder.
Click to expand...
Not weird.

The tighter you string a racquet, the softer(more flexy) it gets.
 
PistolPete23 said:
Which piezo contact microphone do you have? I tried looking for one that could connect to the iPhone but didn’t find any.
Click to expand...
Yeah…in a past life I did A LOT of home recording so I have a bunch of random dongles for when I wanted to record high quality audio but use my iPhone for the video.

I’m using an oldest version Blue Mikey Digital Premium (with 30-pin to lightning adapter) as an interface between the clip-on piezo and the iPhone (used ones are all over the auction site but you have to make sure to get the one with the audio input on the top side, the cheaper model doesn’t have the external audio input). Or an audio interface that doesn’t have its own microphone would work too:

iPad/iPhone Interfaces - Sweetwater

Looking for iPad/iPhone Interfaces? Sweetwater has FREE Shipping and FREE Sweetwater Support for iPad/iPhone Interfaces!
www.sweetwater.com www.sweetwater.com

This looks like my piezo:

And you’ll need a mono 1/4” female to 3.5 mm (headphone) male adapter to couple the piezo to the interface.

And of course an app on your iPhone that’ll tell you the frequency of what it’s hearing like the iStroboSoft app.
 
ChanterRacquet said:
Yeah…in a past life I did A LOT of home recording so I have a bunch of random dongles for when I wanted to record high quality audio but use my iPhone for the video.

I’m using an oldest version Blue Mikey Digital Premium (with 30-pin to lightning adapter) as an interface between the clip-on piezo and the iPhone (used ones are all over the auction site but you have to make sure to get the one with the audio input on the top side, the cheaper model doesn’t have the external audio input). Or an audio interface that doesn’t have its own microphone would work too:

iPad/iPhone Interfaces - Sweetwater

Looking for iPad/iPhone Interfaces? Sweetwater has FREE Shipping and FREE Sweetwater Support for iPad/iPhone Interfaces!
www.sweetwater.com www.sweetwater.com

This looks like my piezo:

And you’ll need a mono 1/4” female to 3.5 mm (headphone) male adapter to couple the piezo to the interface.

And of course an app on your iPhone that’ll tell you the frequency of what it’s hearing like the iStroboSoft app.
Click to expand...
Sweet, thanks for the info!
 
Klitz said:
Not weird.

The tighter you string a racquet, the softer(more flexy) it gets.
Click to expand...
I switched subjects, the string frequency dropped more on the tighter tension, indicating more relative tension loss. This was not in reference to the frame’s vibration frequency (primary subject of the thread) which seems to not change a whole lot between when it has strings or not. Of course, when it doesn’t have strings is a pretty useless measurement.
 
ChanterRacquet said:
I switched subjects, the string frequency dropped more on the tighter tension, indicating more relative tension loss. This was not in reference to the frame’s vibration frequency (primary subject of the thread) which seems to not change a whole lot between when it has strings or not. Of course, when it doesn’t have strings is a pretty useless measurement.
Click to expand...
Yeah, that’s expected behavior. What’s happening during tension loss is stress relaxation. The molecules rearrange themselves to reduce the tensile stress, ie tension. The higher the starting tension, the greater the driving force for relaxation.
 
It will be interesting to know the duration of the vibration (which is what creates the bigger damage) and not just the absolute value
 
PistolPete23 said:
The higher the starting tension, the greater the driving force for relaxation.
Click to expand...
This was my initial thought as well.

The first racquet off the stringer pinged at 640 Hz, 630 Hz the next morning, then 604 Hz a few days later after my daughter got back from the tournament.

Racquet number two started at 643 Hz (and generally higher main frequencies measured before threading the crosses) and fell to 625 Hz overnight, then hit 599 Hz the few days later with no ball fuzz so I don’t think she hit with this one.
 
mmazzinin1 said:
It will be interesting to know the duration of the vibration (which is what creates the bigger damage) and not just the absolute value
Click to expand...
I’m not convinced the vibration is doing the damage. My phone vibrates sometimes when I’m holding it.

I think the vibration frequency might be reflective of another property that is responsible for damage. Or not, we’re fooling ourselves and it’s really just overuse.

If it was vibration frequency that caused damage, it would vary depending on the racquet AND the person since we all have differently sized arms (that would themselves conduct the vibration differently).
 
I’m curious if vertical vs lateral vibration frequency would be different. For example, hold the racquet such that the face is parallel to the floor, then tap 12 o’clock with a downward force. Next, rotate the racquet so the face is perpendicular to the floor, and tap the 9 o’clock position with a downward force. Vibration frequency is correlated with stiffness. If the lateral and vertical stiffnesses are significantly different, like with the Shift racquets, the difference should theoretically be measurable via frequency …
 
I had to change how I measure the vibrational frequency. Getting iStroboSoft to pick one frequency to report was becoming intractable. So I switched to AudioTools which is capable of doing FFT (fast fourier transform) and show me the amplitude across a spectrum. I also found that a reliable signal was best achieved by striking the string bed instead of the frame, which is more realistic anyway with results not too different from striking the frame. The piezo is being held into place on the highest flat spot on the handle before it splits at the yoke.

I did discover a small change in frequency between hitting the frame on the side versus the top (152 Hz vs. 155 Hz) on the Shift 99L but that's not a large enough difference to be very interesting.

Now, what's really interesting is the difference between striking the string bed in the sweet spot (where the frame isn't supposed to result in vibrating) versus striking the string bed in what I'm going to call a shank spot (anywhere but the middle gives you the same result: low, high, sides).

Below is the spectrum when you hit a shank spot on a Blade 104 v7. You can see a global maximum at 123 Hz (within the field of view anyway) which corresponds to the frame vibration reported by TWU. There are other frequencies too which is one reason the iStroboSoft tuning app was becoming intractable to use. This is without a dampener.

blade-104-v7-shank-604x270.png


Below is the spectrum if you hit the sweet spot on the same racquet. Notice how the frame vibration at 123 Hz dissipates leaving behind the string vibration frequency at 533 Hz. This is without a dampener.
blade-104-v7-sweetspot-604x270.png


So I'm thinking there's no point in worrying about the frame's vibration frequency, even if it is attributable to arm damage, unless you really suck at hitting the sweet spot.

What one might also consider interesting is that adding a dampener attenuated the frame vibration so as to be less than the string vibration even when striking the shank spot! The string vibration frequency also increased by 14 Hz.
blade-104-v7-dampener-shank-604x270.png


There's a lot to chew on.
 
ChanterRacquet said:
I had to change how I measure the vibrational frequency. Getting iStroboSoft to pick one frequency to report was becoming intractable. So I switched to AudioTools which is capable of doing FFT (fast fourier transform) and show me the amplitude across a spectrum. I also found that a reliable signal was best achieved by striking the string bed instead of the frame, which is more realistic anyway with results not too different from striking the frame. The piezo is being held into place on the highest flat spot on the handle before it splits at the yoke.

I did discover a small change in frequency between hitting the frame on the side versus the top (152 Hz vs. 155 Hz) on the Shift 99L but that's not a large enough difference to be very interesting.

Now, what's really interesting is the difference between striking the string bed in the sweet spot (where the frame isn't supposed to result in vibrating) versus striking the string bed in what I'm going to call a shank spot (anywhere but the middle gives you the same result: low, high, sides).

Below is the spectrum when you hit a shank spot on a Blade 104 v7. You can see a global maximum at 123 Hz (within the field of view anyway) which corresponds to the frame vibration reported by TWU. There are other frequencies too which is one reason the iStroboSoft tuning app was becoming intractable to use. This is without a dampener.

blade-104-v7-shank-604x270.png


Below is the spectrum if you hit the sweet spot on the same racquet. Notice how the frame vibration at 123 Hz dissipates leaving behind the string vibration frequency at 533 Hz. This is without a dampener.
blade-104-v7-sweetspot-604x270.png


So I'm thinking there's no point in worrying about the frame's vibration frequency, even if it is attributable to arm damage, unless you really suck at hitting the sweet spot.

What one might also consider interesting is that adding a dampener attenuated the frame vibration so as to be less than the string vibration even when striking the shank spot! The string vibration frequency also increased by 14 Hz.
blade-104-v7-dampener-shank-604x270.png


There's a lot to chew on.
Click to expand...
Never expected to see a Fourier transform on TTW lol. Good stuff!
 
ChanterRacquet said:
What one might also consider interesting is that adding a dampener attenuated the frame vibration so as to be less than the string vibration even when striking the shank spot! The string vibration frequency also increased by 14 Hz.
blade-104-v7-dampener-shank-604x270.png


There's a lot to chew on.
Click to expand...

This is the most surprising result to me, that a dampener, which resides on the strings, can also dampen frame vibration …

On another note, frequencies in the 120s is at the low end of the spectrum. The Blade 104 should play really comfortably!
 
socallefty said:
Why not read some of the scientific research also.

pubmed.ncbi.nlm.nih.gov

The effect of tennis racket string vibration dampers on racket handle vibrations and discomfort following impacts - PubMed

In this study, we evaluated the effect of the use of tennis racket string vibration dampers on racket handle vibrations, and perceptions of hand and arm discomfort experienced by tennis players owing to stationary racket impacts. Twenty tennis players (10 males, 10 females) aged 18-29 years...
pubmed.ncbi.nlm.nih.gov pubmed.ncbi.nlm.nih.gov
Click to expand...
Sure thing, I’ll read when I get to work tomorrow and have access beyond the abstract. Of course, earlier in the thread I hypothesized that vibrations have jack all to do with arm discomfort, so my analysis of my very unrefined experimental data shouldn’t be interpreted as anything more than I’m getting my feet wet and would welcome any input to help refine my experiments, such as the article you linked.
 
ChanterRacquet said:
Sure thing, I’ll read when I get to work tomorrow and have access beyond the abstract. Of course, earlier in the thread I hypothesized that vibrations have jack all to do with arm discomfort, so my analysis of my very unrefined experimental data shouldn’t be interpreted as anything more than I’m getting my feet wet and would welcome any input to help refine my experiments, such as the article you linked.
Click to expand...
There are several articles listed on that link on the same topic also. Read them all.
 
ChanterRacquet said:
What do you make of them? Since the purpose of science is to question, what do you think remains unanswered after reading the articles yourself?
Click to expand...
I basically believe the articles I’ve read that dampeners just remove high frequency string vibrations and not the low frequency vibrations that come from impact shock and transmit through the racquet to the arm. It seems to match my experience from playing tennis for almost fifty years with and without dampeners where the only thing they seem to do is remove the annoying high-pitched twang noise you get at contact.

If there is some dampening of impact shock done by dampeners, I don’t think it is material enough to make a difference where it makes a stiff racquet or stiff strings much more comfortable. If I want more comfort, I need to switch to a comfortable stringjob or a more comfortable racquet. I do believe that the TWU measurements of vibration frequency seem to have a better correlation to racquet comfort than RA stiffness values.
 
I've switched to bouncing a tennis ball on the ground with the racquet 5 times for a more relevant measurement. In doing so, I get much stronger racquet vibration peaks in the FFT. It is also clear a dampener does not affect the magnitude of that frequency (123 Hz in this case).

No dampener
blade-104-v7-5-bounce-604x270.png


Dampener
blade-104-v7-5-bounce-damp-604x270.png
 
ChanterRacquet said:
Measuring across 5 Blade 104 v7, I got consistent results for each individual racquet but across all 5 a range between 123-133 with TWU at 127. Oddly enough, the heaviest was the 133, iirc.
Click to expand...
Yeah, I think it makes sense that if there’s a spread in RA stiffness, then there would also be variation in vibration frequency, since the two are strongly correlated. TWU reports numbers for just a single racquet.

As a gut check, I measured the frequency for the stiffest racquet I have, a Solinco Blackout Xtd. 161 Hz, pretty high on the spectrum.
 
I measured vibration frequency on all the racquets. FT Saber has the highest by far, at 182 Hz. No wonder my elbow is sore sometimes after playing with it extensively. Lowest frequency is VCore Pro 97H, which I haven't yet hit with. The classic Head racquets, including the PC 2.0, are in the low to mid 130s. The Fischer VP90 is NOS. Debating whether to keep that one or sell it before I string it up.

When I hit with the PS85 for the first time last week, I didn't quite enjoy it. Anything off the small sweet spot felt pretty harsh. Now I know why; the frequency is pretty high!

RacquetStrung (T/F)Vibration Frequency (Hz)
Diadem Elevate FS 98 v2T138
Diadem Elevate FS 98 v2T138
Fischer Pro Mono 95T141
Fischer Vacuum Pro 90F (NOS)135
FT Saber 300T182
Furi Arma Pro 98T132
Furi Arma Pro 98T138
Head Bumblebee Radical MPT135
Head IG Prestige MidT146
Head Prestige Classic 2.0T134
Head Pro Tour 2.0T144
Head Pro Tour 280T132
Prince Graphite Classic 107T138
Solinco Blackout XTDF161
Volkl Power Bridge 10 MidF141
Wilson Pro Staff 6.0 Original (Taiwan)T149
Yonex VCore Pro 97HF129
 
Last edited:
ChanterRacquet said:
Unstrung you’d have to hit the frame.

Given how cheap this setup is, I wonder if they might add it to the racquet matching service.
Click to expand...

I actually just tap the top of the hoop with my Theraband Flexbar. And I found gripping the racquet at the top of the handle gets the strongest signal. Something I noticed is that even though there's a single dominant frequency, there are also other frame frequencies as well that probably contribute to the overall feel and comfort of the racquet. My Furi Arma Pro 98 sometimes causes a little elbow soreness but I have used other racquets with higher frequencies that didn't cause any soreness.
 
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