David, the issue I'm trying to get clarified is simple. Under the conditions I specified, is "sensitivity" proportional to natural frequency.. The consensus seems to be yes. And it has been stated and so far not questioned that if one changes the natural frequency by adding components, like guides, the natural frequency will change (get slower and therefore less sensitive).

Adding things to a blank does not change its natural or resonant frequency. The added components dampen the blank's ability to vibrate. So in that sense all they do is mute or attenuate the vibrations.

Take a bell for example. Ring the bell and hear its tone. Now place your hand on the bell. The ringing will immediately attenuate, but you are not changing its natural or resonant frequency.

Rods are no different. Adding guides to the blank are not changing its frequency. They are muting or attenuating and nothing more or less.

If you glue rubber pads to a bell, they do not change the bell's natural or resonant frequency. All they accomplish is to prevent the ability of the bell to vibrate. Its an amplitude thing.

But where rods are concerned, less is better for sensitivity or the blank's ability to vibrate easily or not.

An uncoated rod is more sensitive than a coated rod of the same model. A rod with fewer guides can vibrate more easily than rods with more guides of the same model.

So for those who load down a rod blank with coatings, lots of guides, thread wraps extending beyond the guide feet, rod wraps, art work, etc. are simply killing the rod's ability to vibrate. Less is better if you want a sensitive rod blank.

Directly to your question, yes, natural frequency or resonant frequency of the rod blank does directly relate to its sensitivity or ability to transmit vibrations from the input at tip to the hand. Higher frequency blanks transmit vibrations better and more easily than lower frequency blanks which tend to absorb some of the input signal and is lost and not transmitted down the blank to the hand.



Edited 3 time(s). Last edit at 07/27/2021 11:57AM by Kent Griffith.

"Adding things to a blank does not change its natural or resonant frequency." Kent, don't put a lot of money betting that mass added to a blank does not change its natural frequency. Why do you think that Bill Hanneman added mass to the tips of blanks/rods for his CCF process? To get the natural frequency of the system down to where it could be easily measured without expensive/complex equipment. The more mass he added the lower the natural frequency.

I know nothing about bells. But I submit that putting one's hand on the bell does not constitute adding mass to it. You are affecting its damping, but not its mass. When you add guides to a blank it adds permanent mass to the system and its natural frequency will drop.

"The natural frequency, as the name implies, is the frequency at which the system resonates. In the example of the mass and beam, the natural frequency is determined by two factors: the amount of mass, and the stiffness of the beam, which acts as a spring. A lower mass and/or a stiffer beam increase the natural frequency (see figure 2)." from [www.newport.com]

This is true for any spring/mass system.

Mick,

Yes, adding components will cause the frequency of the rod to decrease. There are two ways to calculate the frequency of the wave. 1. frequency = waveSpeed / wavelength. 2. frequency = 1/(2*Pi) * SquareRoot(elasticProperty / inertiaProperty). I have not derived the frequency for something like a rod blank (It's not a simple system), but I suspect you should find something like the modulus of elasticity of the blank material appearing in the elastic property of the calculation, and something like the moment of inertia in the inertia property part of the calculation.

By adding components, you are not changing the blank material or the medium for the wave (your components are like buoys on a water wave in this discussion), so that part of the calculation will not change much. However by adding mass you are adding inertia. Since the inertia property is in the bottom of the fraction, as the bottom of the fraction gets bigger, the value of the fraction gets smaller, so the frequency decreases.

You can see the same effect in guitar strings. Each string is a different thickness, i.e. a different density. The most dense string plays the lowest note, i.e. frequency at the same tension. For a stretched string frequency = 1/(2*Pi) SquareRoot(tension / linearDensity) where the linear density is mass per unit length.

The parallel here is that as modulus of elasticity goes up, the frequency goes up. As inertia goes up, the frequency goes down. As the frequency goes up, "feel the bite" sensitivity goes up. As frequency goes down, "feel the bite" sensitivity goes down.

You can measure the frequency at each step of the build and watch the frequency drop. You can also feel what is going on by lightly brushing the tip over carpet or other textured surface.

The added components also do not damp the vibrations, they have the opposite effect of causing the vibrations to take longer to damp. One thing you might notice in your "feel" test is that the signals feel a bit more noisy as mass is added to the rod. This is because it is taking longer for the background noise to dissipate, and the signal is additional becoming weaker and broader causing it to stand out less from the background.

Edit: My 2Pi's were in the wrong part of the fraction



Edited 1 time(s). Last edit at 07/27/2021 08:39PM by Joe Vanfossen.

"When you add guides to a blank it adds permanent mass to the system and its natural frequency will drop."

""one changes the natural frequency by adding components, like guides, the natural frequency will change"

"Yes, adding components will cause the frequency of the rod to decrease."



Unless the substrate is changed, how can its natural or resonant frequency change?

Are additions changing the rod blank itself?



Edited 11 time(s). Last edit at 07/27/2021 03:59PM by Kent Griffith.

Kent, it's physics, it's a spring mass system, and mass is part of the equation for natural frequency. Just like your pickup truck. Load it with a thousand pounds of sand and it will move up and down in response to road changes much slower than it will when unloaded.

Go to the web site I quoted from, or do other searches for spring/mass systems and natural frequency.

Unless the substrate is changed, how can its natural or resonant frequency change?

Are additions changing the rod blank itself?

They are not changing the blank, but they are changing the system. And the system is what a built rod is in comparison to a bare blank. Think of it in extremes, like Hanneman did. He added so much mass to the blank that it brought the natural frequency down from something like 400 cycles per minute to less than 60, so they could be counted by simple observation with a stop watch.

The problem with changing the system to the extent he did was that one could not see the effects of the typical changes one does to blanks to build a rod. I am very confident he could not tell the difference between a system with titanium guides and one with SS guides. If we can measure what I will call the "native" natural frequency, without artificial mass being added, then we can see what effects the components we add have on the system. AND, if sensitivity is proportional to natural frequency, we can confidently build the most sensitive rods. Without wasting money on what might or might not be worth it.

Kent,

Outside looking in I think it is meant that they are measuring the frequency of the rod and not arguing the blank itself is changing. As you add components to the blank they then are comparing the natural frequency in that state vs. the natural frequency in the raw blank state.

NF of "X" vs NF of "Y" where Y=X+components.

The substrate is not changed but the properties of the sum is. So the physical impacts of the added components and the delta of frequency of the assembly vs blank frequency.

Yes, Aaron, and since we fish rods and not blanks, the more we can know about the the tradeoffs between mass savings and cost with the components we add, the more effective, efficient, builders we will be.

I would say some here are actually measuring the damped oscillation frequency. I don't know the damping factor for normal rod blank construction. If one did he could calculate the true natural frequency.

Only when the damping factor is zero does natural frequency equal resonant frequency. A damping factor of zero doesn't occur in the real world. In some cases it may be close enough to ignore. I rather doubt that is the case with a rod blank, leave alone a finished rod.

I would submit this is a case where most will gain a lot more by experimentation and testing than measuring and math.



P.S. Michael, where did you get the 400 CPS from? Emory was talking numbers much lower, lower than the human hand can detect. Your numbers are at least getting somewhat close to the threshold. I tried to point out we are much more sensitive to an impulse, and that is what we should consider a fish nibble/bite/hit, but that didn't go far.

Russ in Hollywood, FL.

Russell, I was working from memory on 400 cycles per minute, not seconds. But I could be mistaken. But please keep in mind that I'm working on clarifying the issue of "is sensitivity proportional to the natural frequency of the blank" for the conditions I've specified. Damping factor, IMHO, has nothing to do with it. What is the difference between experimentation and measuring?

I submit that the "true natural frequency" is what we measure when we deflect the tip, release it, and measure the response. With no mass added to it.

Suppose you discover the natural frequency of a blank, but you don't like it. Could you alter its frequency by chopping some off the tip or the butt of the rod, but what Measurable Benefit would this accomplish besides being able to report the new natural frequency of your rod to friends and bystanders? Also, does the diameter, weight, or elasticity of the line you use cause any variation in the rod's frequency, and if so how and how much?

I like the natural frequencies of all blanks and rods.

By chopping it you will change its weight, power and action which will most likely be a more significant change than the frequency, which will change. But I don't chop blanks. With the multitude of blanks available it is unlikely that I won't be able to find one I like. I think chopping a blank to acheive a different natural frequency makes absolutely no sense.

It is my position that knowing how the natural frequency changes with the components added is more important than knowing the initial natural frequency.

Only components fastened to the rod will change its natural frequency. Line characteristics have nothing to do with the blank/rod physical characteristics, of which natural frequency is one. Keep in mind that the discussion is not about any casting feel or response or efficiency.. It's only about sensitivity as I defined it in the first post.

Regarding my comment about 400 cycles per minute, and Emory having lower numbers: I expect Emory was dealing mostly if not totally with fly rods, possibly cane, likely at least some glass, and the natural frequencies for those would be significantly lower than 400. Probably 200-300? I haven't gone back through writings to check.

By adding mass, you have changed the system. The natural frequency for a cantilever with no load is different than the natural frequency for the same cantilever with a distributed load. The frequency for the cantilever with a distributed load is lower. Whether you conceptualize the effect of the added mass as 'effectively' altering the linear density of the medium (blank/rod) or as a system that is now carrying a load distributed at specific points along the blank, the effect is the same. The resonant frequency of the system will decrease due to the extra inertia.

At the end of the day, you have not altered the elastic properties of the medium, but you have altered the inertia of the system.

Where can I find a credible source which reports casting distances achieved by various rod frequencies? Or do rod frequencies chiefly influence accuracy?

Not gonna take the bait!



Edited 2 time(s). Last edit at 07/30/2021 09:13AM by Kent Griffith.

In my mind, sensitivity is defined as the magnitude of vibration at the point of which the user is in contact with the rod. The higher the magnitude the more sensitive.

If this is the case then measuring magnitude with a micro strain gauge or magnetic field could work for actual data. If recording resistance and the wave length recorded on the data logger is taller the magnitude is higher. The closer together the peaks the higher the frequency. If we test enough rods the impact of both magnitude and frequency could be defined. Something like this [micro-measurements.com] could be modified to log real time strain in a logarithmic graph. The other way could be a precise induction loop. This would be a very cool project.

Edit: Something pliable like this may work much better. It may even work wrapped onto the rod. [ieeexplore.ieee.org]



Edited 1 time(s). Last edit at 07/30/2021 09:32AM by Aaron Petersen.

Phil, I'm only interested in the conditions and question I wrote in the original post.

Aaron- Thanks for the ideas, but sophisticated tools like this are not necessary. I am very familiar with strain gages, even put an array into a running auto engine one time to measure the response of the oil pump under various running conditions. Ironically it was placed on what amounted to a flexible cantilevered beam. Sound familiar? Yes, strain gages would be very accurate and reliable solution, but I don't want to have to strain gage every blank/rod to find its natural frequency.

Michael Danek Wrote:
-------------------------------------------------------
> Phil, I'm only interested in the conditions and
> question I wrote in the original post.
>
> Aaron- Thanks for the ideas, but sophisticated
> tools like this are not necessary. I am very
> familiar with strain gages, even put an array into
> a running auto engine one time to measure the
> response of the oil pump under various running
> conditions. Ironically it was placed on what
> amounted to a flexible cantilevered beam. Sound
> familiar? Yes, strain gages would be very
> accurate and reliable solution, but I don't want
> to have to strain gage every blank/rod to find its
> natural frequency.

The point of the study would not be to publish the frequency of each rod build or blank and use that as a marketing tool. 99% of consumers and end users would be confused and never care. I was simply stating there is a scientific way to answer the question which was posed about correlating frequency and sensitivity. Some people on here even find CCS too burdensome to conduct on every blank or build. There is no way a practice like outlined above would become any type of standard.

I was never proposing that frequency would become a standard or a published number. I think the value of the natural frequency is as a tool to help builders make decisions about cost vs value. With maximum sensitivity at a reasonable cost being the objective.

Michael Danek Wrote:
-------------------------------------------------------
> I was never proposing that frequency would become
> a standard or a published number. I think the
> value of the natural frequency is as a tool to
> help builders make decisions about cost vs value.
> With maximum sensitivity at a reasonable cost
> being the objective.

10-4 I did not think you were. We are on the same team. I agree with what you are looking to achieve 100%. I am just brainstorming how to correlate frequency to sensitivity in order to compare them as requested. My last post was a bit unclear reading it back now. I am not negating what you were seeking. Merely looking to set a correlation standard to objectively educate ourselves as to how frequency and sensitivity relate. Right now if manufacturers posted numbers for frequency it would be of little value as we have no idea how to compare that to real performance to my knowledge.