The theory of Harmonic Balance is very this: when a sword strikes an object the sword vibrates in a wave. Every wave expressed by a solid object that is longer than it is wide has Rotational Nodes where the wave reverses at either end of the object. On swords the rotational node on the blade is what is commonly referred to as the Center of Percussion. I had thought his was first recognized and described in modern times in Richard Burton’s ‘Book of the Sword.’ However the COP is identified in Capt. Settimo Del Frate’s “Instructions for the fencing of the Sabre and Sword of Prof. Giuseppe Radaelli” of 1876 as follows:
“The saber is also divided in two centers, namely, the center of gravity and center of percussion. The center of gravity is the place on the blade where half the mass the weapon is on each side of the point. The center of percussion is the part of the blade which produces greater effect in the blow of the edge.” Book I, Ch II, Sec 3.
Examination of antique swords has shown that overwhelmingly that the Node at the opposite end of the sword tends to be located where the sword is gripped by the strong-hand of the user. In practical terms this means that shock is not transmitted to the hand when striking with the sword. This location of the rotational nodes creates the effect that we now refer to as ‘Harmonic Balance.’ This has been observed in actual antiques by not merely myself but by researchers such as Craig Johnson of Arms and Armor- also curator of the Oakeshott Collection. Other respected researchers/re-creators such as Vince Evans have also noted this phenomenon. Harmonic Balance is independently confirmed, demonstrable, repeatable and fully meets the standards of scientific proof.
This can be tested for quite simply- Grip the sword firmly with the unsheathed blade pointed straight up, then use your off-hand to strike the pommel firmly. You will observe a spot on the blade that vibrates markedly less than the rest of the blade- this is the ‘Center of Percussion’ or ‘Sweet Spot.’ If you feel a corresponding ‘dead spot’ of minimal vibration under your hand gripping the hilt then the sword is what we call ‘Harmonically Balanced.’
The use of the term Harmonic Balance in marketing describes a real and important characteristic found in good quality reproductions and antiques alike. In the past it has been claimed that these swords cut better due to reduced energy loss from vibration- this was not ‘hype’ in the sense of deliberately misleading the customer but rather a mistake that proceeds from a false assumption. Good swords cut better than bad ones, and good swords have proper Node location, or in common sword terminology we would say they are ‘Harmonically Balanced.’ They do not cut better because of Harmonic Balance, it is simply one of many factors that make a sword ‘good.’
A final Note- the term Harmonic Balance is part of the lexicon of the sword-making and sword using culture- it has become a technical term widely used in the community via the internet. It is not the best term for this phenomenon but has become so widely distributed that attempts to employ more technically accurate terminology have been overwhelmed by inertia- however much I wish it otherwise we seem to be stuck with this imperfect terminology. I will say however that I didn’t invent this terminology- it was already in use in the sword-making community when I became a sword-maker. It was passed on to me in the early ’90s by sword-maker Chuck Sweet, whom I believe had it from Ike Roe. Mr. Roe had observed these qualities in antiques but I cannot say with any certainty whether the terminology is one that he invented to describe an observed phenomenon or whether it was passed to him by some unknown person and subsequently verified by observation.