A Brief Survey of Various Attempts at Reducing Vibration in Baseball Bats
Several bat manufacturers have tried a variety of vibration absorbers in an attempt to minimize the vibration in the handle that produces the painful sensation of sting for hits away from the sweet spot. Wearing batting gloves and wrapping the handle with leather or rubber grip helps to reduce the vibration slightly, and there are some devices you can attach to the knob that supposedly reduce sting. However, I will limit my survey below to modifications of bats themselves, methods which are designed to much more effectively reduce the vibration at a specific frequency.
Easton V.R.S. (Vibration Reduction System)
In 1991, Easton collaborated with engineering firm Rousch-Anatrol to develop a Vibration Reduction System (V.R.S.) for their LX8-V youth bat model. The V.R.S. was also used in the 30-inch youth version of the Black Magic. In 1996, when I was a physics professor at Kettering University, I visited one of the engineering departments at Rousch-Anatrol and was shown one of the Easton V.R.S. bats. Later that year, I managed to find a couple of LX8-V 30-inch youth bats at a used sporting goods store, and cut one of them open to look at and study the vibration absorber. The photographs below show what it looks like.
(TOP) Scan of the label from the wrapper of a new Easton LX8-V youth bat, a schematic of the V.R.S. absorber showing its location in the taper region, the frist flexural bending mode of the bat. (ABOVE RIGHT) Photographs of two Easton LX8-V youth baseball bats, with one cut apart to show the V.R.S. absorber in the taper region of the bat. (RIGHT) close-up photo of the vibration absorber.
The Easton V.R.S. is essentially a cantilever-type mass-spring vibration absorber, located in the taper region of the bat. A mass-spring vibration absorber (often called a dynamic absorber or tuned-mass damper) is just a secondary mass-spring system attached to a primary structure, and tuned so that its natural frequency is the same as the frequency which needs to be reduced in the primary structure. When the primary structure is driven at this target frequency, the attached absorber vibrates. Some of the energy is dissipated in the absorber, but the primary effect is that the absorber motion exerts a force on primary structure that cancels -- or greatly reduces -- the vibration amplitude. Such devices are widely used as a vibration control solutions to industrial vibration problems
The location of the absorber in the taper region of the bat coincides with the location where the vibration amplitude is maximum for the first bending mode. The V.R.S. absorber is very effective at reducing the vibration of the first bending mode. This can easily be demonstrated by holding the bat lightly in one hand at the handle and tapping the barrel on the ground. A normal aluminum bat will vibrate and produce an easily detected buzzing vibration in the handle, while a bat with the V.R.S. will hardly vibrate at all, and the difference in feel is very noticeable. However, while this device greatly reduces the amplitude of the first bending mode vibration, it does not significantly reduce the second vibrational bending mode which I believe to be more important to the perception of sting.
The presence of the absorber mass in the taper region increases both the weight and the moment-of-inertia (MOI) of the bat. Larger MOI bats are more difficult to swing, and since the late 1990's the trend for youth bats has been to go lighter and lighter, to the extent that you can find 30-inch youth bats with weights as low as 16 ounces. In spite of the effective reduction in the vibration of the first bending mode, Easton abandoned the V.R.S. absorber by the late 1990's because it added too much weight to a youth baseball bat.
Louisville Slugger Sims Sting Stop
Since the early 1990's, certain Louisville Slugger youth bat models have employed the patented Sims Sting StopTM in the knob. This vibration absorbing device is a rubber piece (see photo at right) that essentially acts as a mass-spring vibration absorber (similar to the Easton V.R.S. system except that the mass and spring are formed from a single piece of rubber instead of being a metal mass attached to a rubber spring).
Like the Easton V.R.S., the Sims Sting Stop is tuned to reduce the first bending mode, and it does so rather effectively. This can easily be demonstrated by holding the bat lightly in one hand at the handle and tapping the barrel on the ground. A similar aluminum bat without the Sims Sting Stop will vibrate and produce an easily detected buzzing vibration in the handle, while a bat with the Sims Sting Stop will hardly vibrate at all, and the difference in feel is very noticeable. But, unlike the Easton V.R.S., the Sims Sting Stop in the handle does not appreciably increase the weight or moment-of-inertia of the bat, and so it can be implemented into lightweight youth bats. Louisville Slugger youth bats with the Sims Sting Stop are still readily available today.
Make a high speed movie of the bat vibrating with and without the sting stop???
Worth ACX Piezoelectric Damper
In 1998, Worth collaborated with ACX (a company specializing in vibration control using piezoelectric materials) to produce the Copperhead ACX. This bat had a piezo-electric circuit on the handle (underneath the leather grip) in the region of the top hand. PHOTOGRAPH. A piezo-electric material is a special ceramic that when squeezed, produces a voltage proportional to how much it is squeezed. This circuit-absorber converts vibrational energy in the handle into electrical energy which is then dissipated through resistors; a red LED in the knob lights up with the bat vibrates and the energy is being dissipated. This is kind of a cool marketing ploy - you can tell when the vibration absorber is working because the red LED in the knob lights up.
The performance of this piezo-electric vibration absorber was described in the October 1998 issue of Sound and Vibration magazine and I've included a couple of graphics from the article at right. From this article, I found two points of interest that backed up my own research which focused on the second bending mode as the target for vibration reduction to minimize sting. First of all, the location of the ACX piezo-electric circuitry was at the location on the handle where the second bending mode has a maximum negative strain, in agreement with my own findings. Secondly, perhaps as should be expected due to its location, the vibration reduction (indicated in the graph) is more than twice as effective for the second bending mode than for the first bending mode.
In December of 2006, I managed to find a used 33-inch, 29oz Worth Copperhead ACX on eBay took it to my lab for testing. My measurements of the damping verify that the piezo-electric circuit damper targeted the second vibrational mode, but it does not provide as much damping as other the other mechanical methods. Following the 1998 college baseball season, the NCAA instituted the minus-3 rule (weight of the bat in ounces must be no more than 3 units less than the bat length in inches) and reduced the allowed barrel diameter to 2-5/8". The ACX Copperhead was a minus-4 with a 2-3/4" diameter barrel so it was not legal for play under the new NCAA rules. I don't know why this damping technique wasn't applied to another model bat which satisfied the new NCAA rules, but it seems that Worth abonded this approach after its initial introduction in 1998.
Easton ConneXion - 2 piece handle + barrel construction
Marucci Bats and the Albin Harmonic Damper
In March of 2004, a Louisiana inventor by the name of Joel Albin was awarded a patent for a baseball bat knob with a vibration absorber that was designed to reduce the sting from unwanted vibration. Essentially, Albin redesigned a larger knob for the handle of a metal baseball bat to fit the Matthews Harmonic DamperTM a mass-spring vibration absorber designed to reduce vibration in compound hunting bows.[12-13] The text description in Albin's patent shows a complete lack of understanding about how bats vibrate and how vibration in the handle causes the painful senstation of sting. However, the device appeared to work fairly well, though the Matthews Harmonic Damper was tuned for archery bows, and not for baseball bats. From July 2004 through November 2007, I did a fair amount of vibration testing for Albin's marketing group, to help improve the performance of Albin's damper for baseball bats. This was an opportunity for me to test my understanding that the cause of painful sting in the top hand was due to the second vibrational mode of the bat. I measured the vibrational mode shapes and frequencies for a collection of baseball and softball bats to determine the range of frequencies that needed to be targeted, and determined values of the the mass and stiffness of the vibration damper in order to more effectively reduce the unwanted vibration in a bat. My recommendations were implemented in the first generation of bats sold by Albin Athletics.
Albin tried to pitch his vibration absorber to several bat manufacturers, but was unable to broker a satisfactory agreement. So he formed his own company, Albin Athletics and starting making and selling his own line of aluminum baseball and softball bats which went commercial in 2007. His bat company was not a commercial success, but it did attract the attention of a successful nearby Louisiana wood bat manufacturer, Marucci Bats, that was looking to expand into the metal bat market. Marucci bought out Albin Athletics and began selling metal bats with Albin's vibration damper. I did additional testing for Marucci in 2010 to help them tune the second generation of the damping device now used in bats like the popular Marucci CAT-5. The current version of the damper (see photo at left) still has a metal mass piece surrounded by a rubber spring, but fits into a much smaller plastic knob.
There is an interesting beneficial side effect to the addition of a vibration absorber in the knob. The absorber weighs a couple of ounces to the total weight of the bat. In order to keep the total bat weight similar to other bat models (for example, a minus-3 drop bat would weigh 31-oz for a 34-inch length) weight must be removed from the barrel end of the bat. The reduction of weight in the barrel end and increase in weight in the knob of the handle means that the balance point of the bat shifts toward the handle, and the Moment-of-Inertia of the bat is lowered. This means that Marucci bats with the absorber in the knob, may be swung with more control, and with faster bat-swing speeds. Of course, a bat with lower moment-of-inertia is less effective at transferring momentum and energy to the ball, but this deficiency is easily made up by increasing the elastic properties of the barrel so that the overall performance of the bat is unchanged, while the player can swing the bat with greater control and with greater confidence that they won't get stung.