Emory

In another thread you stated, "I also do not make the frequency measurements by adding weight to the blank as in the CCS. I think that this is also a case where it may work OK with fly rods but results in very misleading measurements with other types of rods. "

I would be very interested in learning exactly how you make these measurements and how you use the results. It is my current opinion that knowing the natural frequency value of a rod is of very little if any use without some knowledge of both K and m.

On the other hand, fly rods are significantly different. Here, I believe, the fundamental purpose of the fly line is to adjust the frequency of one's fly fishing outfit (i.e., rod + line) to what the angler prefers (PPF = Personal Preference Frequency). I presume you are aware of the equation ERN=ELN for a "CCS balanced outfit". While this is "balanced" with respect to the power of the rod and the weight of the line, there is no assurance that such an outfit will "feel right" to the angler.

This brings in what I call the Delta factor, Delta= ERN-ELN and represents the "mismatch" between the CCS value and PPF. This is compensated for by the angler choosing a different ELN line. The net effect of this choice is to change the frequency of his "outfit", and in the region of fly lines, a change of one AFTMA Line No. changes the frequency of an outfit by approximately 5 cps. I believe all of this effectively explains the what, where, and how anglers arrive at a "good feeling outfit". As you can see, frequency is at the base of all this, but any knowledge of the fundamental frequency of a rod is not important.

I have not seriously considered other types of rods, but I would expect the same types of interaction of PPF and ERN would be relatable to the weight of the lure an angler would prefer to use with his rod.

Bill,
The way I measure a rods or blanks resonant frequency, or natural frequency or first harmonic whichever you prefer to call it, is to lock down the butt of the blank or rod, deflect the tip and then release the tip and let it oscillate through a light beam that is focused on a photo transistor. The output of the photo transistor I connect to an oscilloscope and an electronic counter. The oscilloscope lets me view what is occuring and the counter gives me an accurate digital readout of frequency. I do not really need both a scope and a counter either one by itself would make the measurement but I have both so I connect both up.

If you remember back when you were developing Common Sense Frequency you called me a couple of times and we had a couple of long conversations about the approach that you took. At the time I had recently finished making a couple hundred frequency measurements for a physicist at HP Labs in Palo Alto. He attempted to add a series of weights to the tip of a rod to slow the oscillations down so they could be counted by eye. The theory was that by measuring the resonant frequency with each weigh and then pluging these values into software that he had developed that would do a mathamatical regression back to zero weight he could tell without any equipment what the actual resonant frequency was. He had planned to make the software available to everyone free. The problem is it did not work. The relationship between added weight and resonant frequency was too non-linear for his regression math and we got answers that were all over the map and basically useless and we were unable to come up with a different model that worked.
As a result of this work I do not believe that there is a simple or useful relationship between resonant frequency and weight added to the tip of a rod that will accomplish what you are trying to accomplish with Common Sense Frequency.
I think that what loads a fly rod or any other rod and determines the velocity of the tip or the resonant frequency when loaded by a line or a lure is not weight at all it is inertia.



Edited 1 time(s). Last edit at 01/10/2010 09:03PM by Emory Harry.

Bill,
I agree with you that resonant frequency measurements, just like action angle measurements of even power measurements are not very useful absolutely or as a single measurement. But I will argue that in the correct context, in comparison to other measurements, most importantly other resonant frequency measurements, they are the most useful of all the measurements that we make. They are the most useful because everything shows up in the resonant frequency, power, length, action, even material.
I know that you have read the works of Dr. Spolek and Dr. Hoffman. They both think that resonant frequency is the first or second most important property of a rod.