I am writing this post to introduce a process, using cheap almost universally available technology, that can accurately measure the true natural frequency (TNF) of a blank or rod. It has been casually mentioned before on the forum. The reason for wanting to know the true natural frequency is that most knowledgeable builders believe that while one cannot measure sensitivity, it is proportional to the true natural frequency of the blank. TNF is the frequency at which a blank or rod will vibrate when the butt is solidly mounted and the tip deflected and let go. There is no weight attached to the blank or rod to alter its TNF. It will work with all types of blanks/rods, fly-spin-baitcast-etc.

What it can do: It can tell whether your money spent on premium blanks is getting you a higher response speed blank or not. It can tell you how much your blank slows when guides are added. It can help determine whether smaller, lighter, possibly more expensive guides/tiptops are justified with respect to response speed vs. price. It can determine how much wrap practices (weight) affect the response speed of a blank.

I am not going to discuss the value of the process or its relationship to other frequency determining processes. If you think it is of value to know the TNF of your blanks or rods, then use it. If you don't, forget it.

Yet unanswered questions: How does rod geometry (power and action) affect TNF if at all? How does rod orientation affect TNF if at all? (this relates to the spine orientation).

What equipment is required? 1. A method of solidly mounting the butt of the blank or rod. This is a very low-force process, so a wrapping machine with the rollers pressed against the blank butt works fine. The deflection is just a few inches and there are no safety concerns. 2. An Android cell phone, Kindle, or tablet with a free sound analyzer application. The larger the screen the more accurate the frequency measurement will be. 3. A simple calculator.


The process will work on Android phones or devices like Amazon Kindles. Probably tablets, too, but I have not tried. The larger devices work better because of the larger screens which make reading the data more accurate. The application to be used is the “Audio Frequency Counter,” a free app available on the application store. It is by a company called Keuwlsoft.

The method is to mount the rod securely at the butt, deflect the tip about 3 inches, and let it vibrate while bringing the face of the phone/Kindle into contact with the vibrating tip. Experimentation on the exact process of doing this will be needed to get the feel of it and to generate clean data. What you are trying to do is capture a single cycle of vibration. The app has a time scale so when you get a clean cycle you can determine the period of the cycle in milliseconds. Divide the number 1 by the period and multiply by 60,000 to get the cycles per minute natural frequency.

The app has many settings and experimentation with them is appropriate. Here is what I have had success with:

Measure: Set it to “Period”
Control: The II button stops the recording. The “Zero” button clears the data.
Gain: I have it set at x5, but if another setting works better, use it.
Time/Div: I set it to 20 ms/div. “Div” is the bolder lines on the screen. Between “Div” lines are 4 time sections. So if the period is measured as 4 Div lines and 3 smaller ones, the period is 4 x 30, or 120 ms + 3 x 5, or a total period of 135 ms. 1 / 135 x 60,000 yields a frequency of 444.4 cycles per minute, (444 cpm).
Threshold Level: Set this depending on the signal you are getting.
Threshold Noise: Set this a little below the Level
Direction: Set it to the symbol for rising
Coupliing: Set it to DC
Gate Time: Experiment, but I find that 10 seconds works. You will trying to define a single period. The device will show it in bright green for a few seconds. Then will gather other data, or noise.

I mount the butt of the rod in my wrapper guides with the roller stands set so that the contacts to the blank are set apart a distance equal to 10% of the blank length. Make sure it is very snugly held.

With the rod mounted deflect the tip about 3 inches and let it go, then move the face of the phone/Kindle into light contact with the vibrating tip so that you can get a clean signal that clearly shows one cycle of vibration. That time between the peaks is the period of the vibration, and as stated earlier, divide 1 by that period in milliseconds, then multiply by 60,000 to get cycles per minute.

Mick Danek



Edited 1 time(s). Last edit at 03/14/2022 04:27PM by Michael Danek.

I'd be interested in recovery rate - which this sounds like it will do.
Biut is a few inches of deflection adequate?
Herb

Yes, this is directly measuring recovery rate. The higher the natural frequency the higher the recovery rate. Give it a try and see what you think. IMHO, and after measuring a lot of rods, the deflection distance is insignificant if enough energy is developed to register as a sound to the device/program. This is consistent with the theory of natural frequency.

I used Michael’s method to measure over a dozen blanks. The results were very reproducible, no matter how far you deflected the blank. I played with it for quite awhile and found that deflecting it just a few inches just made measurements easier.

Micheal you made a mistake in you calculations. At 20 ms/division than for the example you gave it should be 4X20 ms (or 80 ms) + 3x5 ms equals total period of 95 ms.
Norm

Michael,
You have obviously spent a considerable amount of time, effort and thought on your TNF measurement process. My hat is off to you for your devotion and willingness to share your findings. It only seems logical that measuring the frequency of a blank or rod in its raw, naked state will produce the most accurate, precise and repeatable measurements versus adding a “prescribed” amount of weight to the tip to slow it down far enough to enable the naked eye to count that diluted frequency. This should be a huge advancement and benefit to many, rod builders in particular. I can’t imagine being the only one who realizes, accepts and benefits from your gracious gift of TNF. Congratulations and a sincere thank you for a job well done!!!

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Michael,
Is my pea brain assuming correctly that the measured TNF of any given blank would be identical whether initially deflected, say, 2in versus 4 or 6in? I would think that although the “tip speed” at the midpoint of the oscillation would be greater if deflected 6in, the tip also has to travel further, whereas the tip speed would be less if deflected only 2in but does not need to travel as far = they would cancel eachother out. Yes / no?

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Sorry I missed that, Norman, appreciate the correction.

Mark, the answer is Yes, TNF will be identical. This might help: [www.newport.com]


"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"

Hat's off. Michael...lots to digest here. Already has the "Norm Seal of Approval". Strong!

Once you have determined the true natural frequency of a rod or blank what's the next step?

I record it for future reference and comparison to other similar blanks,/rods. I note the "conditions," (bare blank, guide models and numbers, grip, tiptop specs, etc) .

Then if appropriate I make decisions on what I want to do with the blank, titanium vs SS vs price, etc. And make future purchase decisions based on the data. Premium blank? higher TNF? Worth the money?

This is a new process with limited data so far, and there are still a few things to learn as I mentioned in the introduction. It is very interesting and so far the results are consistent, repeatable, logical, and consistent with theory.

I am considering building yet another 9wt. fly rod for my light salt-water use and I plead ignorance in determining which frequency of a blank would be best for me? I fly fish shallow estuaries on the east coast of Florida. The fish are often spooky and casts of 60' and longer are often necessary. I usually cast slow-sinking flies tied on #4-6 size hooks with an overweight floating line and I double-haul my casts. What range of resonance in rod blanks would best serve me, and how can I discover this resonance without first buying the blank?

Phil, I have no idea what natural frequency best suits your plans.

It is my opinion that natural frequency has less to do with your probable success than action and power do.

All I can tell you at this point is that if you are looking for the highest natural frequency fly rods. RX7 will likely have a higher TNF than RX6, RX8 higher than RX7, RX10 higher than RX8. Higher TNF means faster response/recovery. Not faster action, which unfortunately a long time ago was defined using terms normally used to describe velocity.



Edited 1 time(s). Last edit at 03/17/2022 06:41AM by Michael Danek.

have you looked at frequency vs axis of deflection?

No, but another builder reports small differences with the blank rotated into another position. That's sort of what I was mentioning in the intro, that I had not determined if spine affects TNF. I will not be surprised if it does. If stiffness changes I would expect TNF to change.

Apparently a blank's resonance has little or nothing to do with the practical performance of a rod, or someone would have mentioned it. What (measurable) benefit can be achieved by altering the resonance of a blank or rod, or is this benefit purely hypothetical?

Phil, you are wrong. The resonance, as you call it, the true natural frequency, as I call it, is a direct measure of the response time of the blank. And when guides are added one can see how the response time increases. One can see whether titanium guide costs are yielding a faster response time completed rod. Most fishermen consider a faster response time a positive characteristic. Think old Ugli Sticks vs new graphite. A really slow response rod cannot push a rope very well. (sorry, couldn't resist)

And if in fact sensitivity is proportional to natural frequency, as so many experts have for many years argued, the higher natural frequency blanks/rods will be more sensitive. I believe this is true. From my measurements I have found that in fact premium priced blank do in fact generally have higher natural frequencies than the cheapies.

If you search the archives of this forum you will see many discussions of natural frequency.

Lots of references to a relationship between resonance, true natural frequency, and sensitivity - but no data. Sensitivity can be measured, and presumably certain frequencies can be felt at lower magnitudes than other frequencies. So far there has been no revelation of which frequency or frequencies are preferable for maximum sensitivity? Practical rod builders appreciate useful facts such as this.

Most rod experts believe that sensitivity is proportional to natural frequency. The higher the natural frequency, the higher the sensitivity. But since sensitivity cannot be objectively measured this can argued forever. (Phil, I challenge you to show me a test that can objectively measure sensitivity) Here (from an old Rodmaker Magazine) is what Dr. Hanneman thought:

"Every fishing rod blank possesses a unique intrinsic property known as it "natural frequency." This is a measure of how fast it can recover from being flexed and is the net result of many undefinable things. The natural frequency, which in the following will be referred to as NFB (Natural Frequency of Blank) is "fixed at its birth." It can never be increased without shortening its length. On the other hand, anything and everything you normally add in converting that blank into a useful fishing tool will lower that value." "As a general rule, the higher the natural frequency, the more efficient the rod. "

By the way, Phil, I do have data, and the data agree with my perceptions and the data consistently show blanks slowing down as weight is added (guides). But my offering the procedure was not to set myself up as a data source. It was to offer a tool to those who want to use it.

I suggest you stop pontificating and do the process as suggested in the original post. Then your opinions might be based on the data that you call for.

If you can't measure/quantify a quality (like rod-blank resonance) why talk about it, except to pass the time? I suppose dang near everything has a "natural frequency", but if you can't perceive this frequency or specify its results why would anybody worry about it? Why don't rod blank makers and dealers to reveal the natural frequency of their blanks to their buyers? This could be a huge marketing coup - or lead to an even larger false advertising lawsuit!

Phil, listen: Concentrate. I can measure/quantify resonance. That's what the process does.

If you don't want to use the process, just forget it.

I'm still waiting for that objective sensitivity test you mentioned.