Defining sensitivity as the transmission of subtle bites to the hand, and resonant frequency as the frequency of free vibration after the tip is deflected and released (butt tightly secured, no weight attached to the tip) , is sensitivity proportional to resonant frequency? In other words, the higher the resonant frequency the more sensitive a blank/rod is?

Michael, I would like to point out that what you, and others on this forum, are calling "resonant frequency" is natural frequency. Resonant frequency is a driven condition from an external force. Think about pushing a child on a swing. When you push at the right time the force becomes additive. The Tacoma Narrows Bridge is a classic example of an external force driving a system's natural frequency.

We used to have a lot of discussion about this stuff a decade or so back. Here is something I wrote back then. I'm adding it because so few gave thought to what people could feel and just concentrated on the rod. It may be of some interest to you.



"I have not measured but I want to be clear. I hear numbers in the range of 100-200 CPM for raw blanks (natural hertz for fly rods it seems from the other posts). So we are saying 1.67 to 3.33 hertz, correct? That is slower than I would have imagined.

There is a fair body of work that has been done with regards to sensitivity of the human hand with various shaped tools made of different materials. I suggested looking at long canes for the blind. One can even look at human nerve limitations.

Work with long canes has shown a somewhat linear performance increase from various materials such as fiberglass to aluminum but more of a quadratic leap with graphite. Light and stiff are of prime importance. Some of us are old enough to have fished with metallic rods and certainly fiberglass and graphite. I don't think anyone is doubting the superior performance of graphite nor the light and stiff part.

IIRC the hand is most sensitive around 250 hertz and the middle finger has the most feeling. Look at it this way, can you both hear and feel braid singing through your guides on a hard running fish? Now we know we can't hear a few hertz. Truth is our hand can't really feel it either. IIRC the range is something around 8-500 hertz. Therefore it should be clear that vibrations don't travel up the rod at its natural frequency. (Today I would suggest something like a spinner baits blade could vibrate at a multiple of a blank's natural frequency and set up a resonance)

It is also known that some "sensors" are directly related to muscle action and some are not. The good news is we respond to impulses more strongly and I'd consider a fish nibble an impulse. It makes me wonder if we couldn't tailor the rod to best produce the ranges we feel the most."

Russ in Hollywood, FL.

resonant, natural, whatever one prefers, but I stated the conditions I'm interested in. I'll use natural from now on. I thought I remembered being corrected before when I used "natural."

[www.quora.com]

Natural frequency:

The natural frequency of a system is the frequency at which it oscillates when struck, pinched, or hit ONCE. By saying once, I mean that you don’t keep applying a force whatsoever after the first (and only) strike.

Key observations:

1. The natural frequency depends just from two things: the physical characteristics of the material (e.g. stiffness) and its mass.
This means it does not depend from how violently we hit or pinch the material. Indeed, as you pinch a string, it produces the same sound irrespective of the force with which you pinched it. What you hear is the natural frequency of the string. If you pinch it strongly, it just sounds louder but the frequency stays the same.
2. The natural frequency of an object is not unique, in general. You get one natural frequency for every degree of freedom the body possesses.

Resonant frequency:

It is strongly related to natural frequency: indeed, if you apply a driving force which is in phase with the natural frequency(-es), the system starts to resonate: the oscillations will be characterized by a steadily increasing amplitude.

So, natural frequencies and resonant frequency are basically the same concept, just viewed from different point of views to illustrate qualitatively different phenomena.

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[www.physicsforums.com]

Resonance is a condition in which a vibrating system responds with maximum amplitude to a periodic driving force. Mechanical systems (beams, pendula, springs, wine glasses, guitar strings etc) will have a number of possible frequencies at which this occurs. These are the system's natural frequencies of vibration. For example, a guitar string will have a series of possible frequencies where this happens, the lowest is called the fundamental frequency. The other frequencies are at values which are whole number multiples of the fundamental. When resonance occurs, the frequency is often called a resonant frequency. This is just saying that resonance occurs when the driving force has the same value as one of the natural frequencies. A beam can have more than one natural frequency, and therefore can be made to resonate at more than one frequency. An (LC) series electrical circuit will resonate at a frequency given by f= (1/2?)?LC This could be called its natural frequency or its resonant frequency. It doesn't really matter. (It's usually called its resonant frequency.)

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Now that is out of the way- natural frequency and resonant frequency are virtually the "same concept" viewed from different points of view... either term can be used virtually interchangeable because BOTH are externally driven causing the material to vibrate at the frequency or frequencies the material "resonates" at naturally. The two terms are so close as to be irrelevant which is used.

Without getting into the mass of the rods since they are so similar, the harder the rod blank material is, the higher the frequency. The softer the material the lower the frequency. Harder rods transmit vibrations better from input at the tip to the hand, while softer rods will absorb a lot of the input at the tip and will not transmit the vibrations to the hand as well. Rubbery rods are not as "sensitive" as stiffer rods.

So as I see it, the OP is correct: "the higher the resonant frequency the more sensitive a blank/rod is"

A simple tap test and well trained ear can hear the difference.

Now, if you have 2 rods with the same resonant or natural frequency, mass is next in sensitivity consideration. The lower volume mass will vibrate more easily than a heavier volume mass. So lighter and harder and stiffer produces the most sensitive rods.

That's my take on it... of course now a lively debate over terminology might ensue.

Michael, it matters little what we call it when we talk among ourselves. Everyone here knew what you were asking about. I only mentioned it because it could matter if you look for answers in other areas, like long canes.

In general I would say yes to your question. However I would point out that length and strength of the blank will give very different answers in your test but the different blanks might seem equally sensitive.

One of my informal tests is the pitch I hear when I drop the butt of the blank on a hard tile/concrete floor. Length and strength of the blank makes little difference in that test and I would consider it a better method for determining natural frequency. I would say what you are doing is more about damping/recovery.

Question, would you fish with a rod that looked like a tuning fork if it offered a noticeable increase in sensitivity?

Russ in Hollywood, FL.

Has everyone read Emory Harry's work? Lots of good info in here and his articles in RodMaker. Like all good discussions, they work best when everyone works from a common point of reference that is agreed upon. Working from a point you can always go back to helps make comparisons stay relevant, the reason I think the Common Cents system works.
In Mike's case, are we comparing the values of a bare blank vs a rod built in different ways that affect it's resonant frequency, in other words it's change in mass and where that mass is, and than making a common correlation between that and sensitivity felt in the hand?

Russ, every time this subject comes up it seems to get sidetracked into semantics over terminology. I was trying to keep this one on track by getting that out of way as quickly as possible.

We should be able to use natural frequency or resonant frequency or eigenfrequency interchangeably for our discussion here. I just wanted thread to stay on course and more on point is all.

Before a rod can resonate it must be deformed and then relieved of tension. This happens at the precise instant the line is released in a cast, but the effect of the resonance of a rod on a slack (released) line during the cast is so small it apparently defies measurement? The coefficients of friction of guide trains with any particular line during a cast is apparently not a published fact - probably because this is such a minuscule effect. This has not discouraged pure, unfounded speculation or strong opinions.

A simple tap test of a straight unloaded rod can produce a clear tone that is measurable by ear and /or equipment though not necessary if merely comparing relative hardness based on sound comparisons.

We don't have to make this harder or more difficult than that.

I can quickly compare rod blanks by merely tapping them. It tells me what I need to know.

In my profession we use strain gauges for validation of Finite Element Analysis. This topic has made me wonder if there is a micro seismograph that can be wrapped around a cylinder. If so a standard for testing such theories of vibration and sensitivity could be set.

Aaron Petersen Wrote:
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> In my profession we use strain gauges for
> validation of Finite Element Analysis. This topic
> has made me wonder if there is a micro seismograph
> that can be wrapped around a cylinder. If so a
> standard for testing such theories of vibration
> and sensitivity could be set.


Not necessarily because there is still the human factor of sensitivity judgement differences.

Yes we can come up with some well defined fixed values of the materials, but transferring it to a human judgement is where things go astray fast.

I'm mostly interested in the original question, under the conditions specified, is sensitivity proportional to natural frequency? Yes I've read most if not all of the old posts on this subject, Emory, Hanneman, and more. From those I would conclude the answer is yes. Thanks for your participation.

Spencer Phipps Wrote:
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> Has everyone read Emory Harry's work?


I have in great length and you're right he's a 'Must' read when it comes to this subject . Tons of info in the archives on this topic.



Imo the below is correct :

The higher the resonant frequency the more sensitive a blank/rod is . Lighter and stiffer produces the most sensitive rods. Tansferring it to a human judgement is where things go astray fast.



Edited 1 time(s). Last edit at 07/25/2021 03:51PM by chris c nash.

Can a simple tap test differentiate between stainless steel and titanium guide trains? Meaning the sound is significantly different bare blank vs. SS guides vs. titanium guides?

It is doubtful to me they would change the tune of a blank.

I would consider both as merely damping material and that's it as far as the ear goes... so in that sense both would do the same thing to the sound of the blank- merely dampen its ability to vibrate. Equal numbers of each type should produce a similar result.

So to answer your question. No. Not viable as I see it.



Edited 1 time(s). Last edit at 07/27/2021 09:21AM by Kent Griffith.

Thank you, Kent.

Chris,
Like the Common Cents system, Emory's numbers are true and repeatable, human judgement as far as an opinion aren't relevant. A yard stick is a known value, and won't change tomorrow, you can hand that yard stick to anyone in the world and they can produce identical objects using it. Same with a kilogram, kilometer, or what will be the difference in frequency when you add an extra guide to a known blank, if you put the blank in a box and store it for a year, when you test it again the results won't change.

Mick,

The short answer to your question is YES. As mentioned, the caveat is that you need to be comparing blanks of similar length, action, and power. In the context of comparing different build options on the same blank, the one that results in the highest frequency at the end of the build will have the most "feel the bite sensitivity," as I like to call it.

I was hoping you would chime in, Joe.

So if one could measure the natural frequency of a bare blank, then keep measuring as components are added, he can see the influence on sensitivity of the differences in mass between the options. Whether he can actually feel the differences is debatable, but directionally, the natural frequency change reflects a deterioration of sensitivity as the components are added. You know, Joe, where this is going.

Blanks or rods could be frequency measured but it is best to do that at various points along the blank. That is what is done with golf shafts. When measured at various points on the shaft, a specific "shaft profile" can be developed for golf shafts. In that manner a golfer can choose a shaft that best fits his or her desired profile. Example: tip stiff, firm mid shaft, soft butt section, etc. A rod's bend profile traced on a wall somewhat does that, but does not provide frequency data, but rather a visual comparison to other rods and how they bend -- a visual index. could be done for rod blanks. B

You could get exact, numeric frequency data for rods/blanks, but you need a frequency machine and plenty of time to run tests.