Single Frequency Technology - The Whole Story


----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

BY ERIC H. COOK P. Eng.

Introduction

Over the past twenty years "FREQUENCY" has probably become the most used buzzword to hit the golf industrysince the game was invented. Unfortunately it is also one of the most misunderstood words that we use when we talk about golf clubs or golf club shafts. Today I will present a technical definition of frequency, an understanding of what frequency is, what it is not and how it relates to custom club fitting. I will describe the three frequency matching systems presently in use and the relative merits of each system. Finally I will relate frequency to shaft characteristics and discuss how the various systems go about determining the proper frequency for the golfer.

Frequency Defined

Webster's dictionary defines Frequency as; "the number of times any action or occurrence is repeated in a given period". and "in physics,..the number of vibrations or cycles per unit of time". From the second definition we can show that, simply stated, "Frequency is a dynamic (in motion) measurement of shaft flex or stiffness stated in terms of cycles per minute (cpm) of vibration, when the shaft is held firmly in a clamp and the shaft is plucked". The HIGHER the FREQUENCY the STIFFER the SHAFT.

Frequency Matched

The introduction of frequency to the golfing world inevitably brought us the term "Frequency Matched" which has added more confusion. Webster's dictionary defines "Matched" as "...to be equal, similar, suitable, or corresponding to in some way;..". This definition leaves us with a number of possibilities; therefore, Frequency Matched could mean either all the same or all different and as you will see as we proceed, both definitions are used. Think about it and decide for yourself if both definitions can be correct when referring to golf clubs used by any one individual.

The concept of frequency matching is not new but until the introduction of the parallel tip or unitized golf shaft, frequency matching was not a practicable consideration since tapered tip shafts could not be tip trimmed and easily installed in the hosel of the club head.

The book "The Search for the Perfect Swing", published in 1968, suggested that frequency matching could be a better method of matching clubs since this would combine weight, length and stiffness; however, there was no indication as to how this could be done.

It will be both interesting and useful at this point to look briefly at the evolution of golf club matching systems which brought us to the present day.

One of the first patents, related to golf clubs, was issued in the United States to Irving R. Prentiss in 1925. Mr Prentiss matched clubs so that the product of the length and weight was a constant. Note the following quotation from the patent, "It will nearly always be found that a player will have one club in his set of which he is particularly fond and in which he reposes the greatest confidence for the reason that he can consistently play that club successfully". Using this favourite club as a base, Irving goes on to explain the system as a method of matching clubs by dead weight and graduated point of balance. Although this was an improvement at the time, and does not relate to frequency matching, it is interesting to note that all these years later most golfers still have that one favourite club in their set. Nothing much has changed in the last seventy years and very few people have thought about Why that one club is their favourite.

In 1944 Mr. M. Knobel received a patent for a method and apparatus for testing the period of oscillation and, thereby, the moment of inertia of a golf club. Although not related to frequency, the invention purports to provide what is referred to as a measure of feel. Would you not think that the favourite club concept also has something to do with feel?

Mr. T.O. Brandon patented a system in 1958 which relates to correlated and co-ordinated shafts for matched sets of clubs. His invention was based on the premise that the length of a golf club shaft is directly related to the stiffness, weight and shaft characteristics. While this concept was indeed true, the matching process did not produce frequency matched clubs because the head weight was not considered in the formula. Furthermore, as you will see, matching the shafts by themselves is merely the first step towards achieving frequency matching.

The first indication of a method of frequency matching is described in a patent issued to Malcolm L. Murdock in 1968. This system measures the frequency of a shaft with various head weights attached. Each measured frequency is plotted on a graph opposite to the head weight used. The invention states, "To match a set of clubs it is necessary only to ensure that for a given shaft length of any individual club, a weight of club head is selected such as will give the requisite frequency of vibration to the shaft". While the theory sounds good, the resulting clubs are still mismatched because they would have different Moments of Inertia due to the inconsistency of the headweights required to obtain the frequency.

In a 1975 patent, John Arthur Kilshaw provided a method of matching clubs by both moment of inertia and frequency. The matching was to be done using a mathematical formula and a graph. Once again the theory sounds good but because of shaft inconsistency the results would be largely a matter of luck. In fact the patent content states that actual testing of the frequency of clubs made using the formula showed an accuracy of plus or minus five percent. This means that a calculated 300 cpm shaft could actually be anywhere between 285 cpm and 315 cpm which is far outside a useable tolerance.

In 1978 a United States patent issued to Joseph N. Braly covered a system that matches clubs in accordance with a "...predetermined frequency gradient formed by a plot of shaft frequency and shaft length such that the gradient is a substantially straight line that increases as shaft length decreases and the frequency increments between successive shaft lengths along the gradient are substantially equal...". This approach to frequency matching is in keeping with the traditional manufacturing methods which produce clubs that get progressively stiffer as they get shorter. You may recognize this system as the FM Precision Shaft now produced by Brunswick Golf or the True Temper Dynamic Gold shafts which follow much the same system but use a different identification code.

Finally, the most recent entry into the frequency matching arena is the Swing-Sync Single Frequency System introduced in 1982. This system purports to be a method of frequency matching a set of golf clubs to match the golfer's swing and is covered by a Canadian patent issued in 1986.

We will look at these three systems in more detail, but first I would like to discuss the Theory of Frequency Matching so that you can understand each system, and be able to discuss the relative merits of each based on scientific fact.

The Theory of Frequency Matching

The Professional golfer, Custom Clubmaker or other golf equipment specialist is often called upon to make recommendations to golfers concerning the selection of golf clubs. Aside from the aesthetic qualities of a set of clubs, which is in the eye of the beholder, the objective in recommending a particular type of club to a golfer should be to match the golf club by Total Weight, Head Weight, Length, Grip Size, Lie and Shaft Flex to both the golfer's strength and swing tempo, while maintaining the same feel throughout the set of clubs.

It is a well established fact that during the backswing and the start of the downswing, the weight and motion of the clubhead causes the shaft to bend, thus storing energy in the shaft. If the golfer is to hit a good shot two things must happen during the downswing. The clubhead must return square to the intended line of flight, at separation, if the ball is to be hit at the target, and the stored energy must be transferred to the ball if the golfer is to attain maximum distance from the club being used. Ideally, to achieve these two conditions the shaft should be perfectly straight when the ball leaves the face of the club. To fully understand the significance of the last two statements let's consider the affect of shaft flex on directional control and energy transfer separately, beginning with the transfer of energy.

To quote from the Search for the Perfect Swing, "... One definite finding was that different degrees of whippiness do not very much affect the distance the ball can be sent with any club. In a test using three drivers with different degrees of whip (X,R and L Shafts), golfers of all abilities hit their best drives with each club almost exactly the same distance. This confirms theoretical predictions that variations in shaft flexibility can make only about five yards difference to the best possible drive any golfer can hit. Even this is probably an overestimate, because it assumes that the clubhead is `springing forward' on the shaft as it strikes the ball. In fact there is ample photographic evidence to suggest that for good players and bad, for whippy shafts and stiff shafts - the clubhead has already sprung forward to the limit of its travel by the time it strikes the ball.... In that case clubhead speed at impact would not depend on the type of shaft at all, and the distance obtained would not vary." Remember that this quotation comes from research conducted with unmatched golf clubs and I will show you later that clubhead speed does in fact depend on shaft frequency; however, for the purpose of this discussion the above quotation is fairly accurate if we are considering only the distance that the ball is hit

Now consider the affect of shaft flexibility on directional control. It is well established that the wrong shaft can lead to a 20 to 30 yard variation in the line of a drive. Most amateur golfers will normally hook the ball with a shaft that is too flexible and slice or push the ball with a shaft that is too stiff but this result depends on their swing plane. Obviously you are looking for the shaft that hits the ball straight and lets you control ball flight when you want to do something else. Unless the shaft frequency matches the golfer's swing, directional problems will almost certainly result; therefore, it is important that you understand the relationship between shaft frequency and clubface position in the hitting area.