The Heavy Bottom Cap Myth
A lot of people have opinions on Heavy Bottom Caps! But what is the truth? How does science explain what we experience when adding inertia to the bottom of the valve casing? It just so happens that I have invested a fair amount of time, energy, and money finding the answers to these questions. The results are not surprising to some, but unbelievable to others. Today, I'll share with you the psychology behind this controversial subject.
First, let's define a few things. Inertia is the subject of today's discussion so we'll start there. By searching for the definition of "Inertia" on google, I get the following:
a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force. "the power required to overcome friction and the inertia of the moving parts"
This definition is quite vague so let's move to the definition of Inertia according to Isaac Newton's first law:
Newton’s first law states that if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force. In fact, in classical Newtonian mechanics, there is no important distinction between rest and uniform motion in a straight line; they may be regarded as the same state of motion seen by different observers, one moving at the same velocity as the particle and the other moving at constant velocity with respect to the particle. This postulate is known as the law of inertia.
We will use this basic definition as it gives us enough parameters to apply to the inertia value within an acoustic brass musical instrument. There really is more to it, but the basics will be more than enough to get us started.
So what happens when you add an ounce of brass (or any other material) to the bottom of your valve casing? If it is secured tightly (usually with threads), this added mass increases the inertia of the valve casing. And the added inertia reduces the amount of standing wave energy that is transferred into vibration energy. This results in increased standing wave energy to the bell, which increases resonance and amplification. In general, stability of some notes will be improved both on attack and sustain, potential for dynamic range increases, and potential for achieving the natural overtone series of the entire closed system increases.
What does that mean? It will be easier to play the note. It will be easier to hold the note. The note will be closer to the tone color as defined by the tapers and linear relation to air volume within the oral cavity, mouthpiece, leadpipe, and bell.
When I refer to the "note", I'm using a generalization to describe any pitch or pitches affected by the added inertia and resulting added resonance within instrument specific to the location of the anti-nodal high pressure zones within the tubing, pistons, valve casings, etc. This anti-nodal high pressure is present on every pitch beginning with the fundamental and increases in number as we move up to each higher partial. The fundamental creates one anti-node in the center (linear length) of the instrument. The next partial creates two anti-nodes, equally spaced between the nodes, which are the ends of each wave form. The second partial creates three equally spaced anti-nodes and so on.
Any note that creates an anti-node near thin material tubing or features may set that material into vibration if the energy is sufficient to overcome the inertia in that area. Since higher partials have more anti-nodes, we have ever-increasing potential for material vibration as we play higher notes. By adding inertia, in the form of mass or some other mechanical design, the transfer of energy at anti-nodes can be reduced or completely eliminated.
Harrelson trumpets were designed and engineered from the ground up to solve the low inertia problem. And heavy bottom caps existed over one hundred years before I was born. Someone understood and applied this theory long before my great great grandparents were alive. I simply rediscovered the basic theory of inertia and how it pertains to resonating musical instruments in 1992. This is not something I invented nor do I take any credit for the theory. But I have invested nearly 30 years into the application of this theory to achieve MBR, which is Maximum Bell Resonance.
Hopefully, this explanation opens your eyes to the physics side of "heavy bottom caps" and maybe even gives you a glimpse into what is possible. Imagine a trumpet where anti-nodal high pressure zones have no affect on the energy potential of the standing wave and the bell resonates at its full potential. What would the world be like if we were all playing instruments that expressed every bit of energy we so lovingly put into them?
Here's a video diving deeper into this subject...
8/18/2021 09:47:11 am
The horn I played before I discovered Harrelson models I tried some heavy caps another player had. The heavy caps made the horn unplayable above high F. Just dead. I eventually found the horn played best with no caps at all I had a set of super thin plastic ones made to keep debris out of the calve casing and loved the response. On the other hand ….it I take the caps off of the great playing Summit and the similar dead and unplayable situation in the upper register happens. The Harrelson horn plays so so much better with the caps. I can’t explain it but it is very smart to play a horn before buying one. Ha!
8/27/2021 02:34:32 pm
This is exactly why we let the client choose what works best!
8/18/2021 10:07:12 am
If you made an instrument (and I’m sure you have) where anti-nodal points have no effect on the energy potential of the standing wave, would that instrument just sound like a sine wave on each pitch? Is it these high pressure anti-nodal zones effecting the inertia of the horn in different places that gives the trumpet its characteristic should, in addition to the energy that is reaching the bell and being affected by the player, mouthpiece, and bell flair?
8/27/2021 02:41:30 pm
The amount of standing wave energy converted into vibration within the bell crook and tuning slide will often determine how the player may respond. If there is a high percentage of energy transfer, the player usually adjusts their air stream and amplitude of the lips to compensate for notes that do not easily speak, which does in fact change the character of the instrument. Think of this as a "buzzy" or "edgy" sound in most cases, though great players can overcome this tendency with diligent practice and skill.
8/18/2021 02:08:51 pm
It all makes so much sense. Appreciate the valuable information.
8/18/2021 09:55:21 pm
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Inventor, Musician, Educator and Founder of Harrelson Trumpets, Trumpet Momentum and Harrelson Momentum.