(patent applied for)
Sebastian Erard (inventor of the modern pedal harp) said, "The great merit of any mechanism rests on its simplicity." Dynamic Tension Balancing is, I believe, one of those simple yet significant ideas. It's at the heart of my Hybrid Series and for the first time allows the harp maker to control the degree of flex in the soundboard without dampening the sound. Here's the problem I was trying to solve:
Having played a Paraguayan for several years, I know how efficiently these harps produce sound. I also appreciate how light the are (only 7 or 8 pounds). And contrary to popular belief, they don't explode and they stay in tune really well. They are, in fact, well-balanced, mature instruments representing some of the most advanced harp making developments in the world. But they would explode if I strung them like a Celtic harp. So, how to make a "Celtic" harp with the same volume and tone producing efficiency as a Latin-American instrument.
First, the extremes of the frequency range–bass and treble–are the hardest to produce. The Paraguayans do both ends well, being both bright and producing a big bottom end. There are two main ways to get there. One is the size of the box. That's easily accomplished. The other is the thinness of the soundboard. Bass frequencies are propagated more readily in a thin plate than a thick one. You can prove this to yourself by taking two similar pieces of wood, metal or plastic, one thick and one thin. Hold each lightly between your fingers and, with your ear right next to it, rap it firmly with something hard like the back of your knuckle. The thin one will have a much lower pitch. There is a similar increase in the high transients (those parts of the frequency response which give cymbals their brightness and sizzle, for instance).
Second, the soundboard acts like a pump. It pushes air from its surface out into the open air around it and so to your ear. Think of each string as a voice coil in a speaker and the board as the diaphragm. The more it can pump, the more are gets moved and the more sound there is. The normal way to correct for increased tension on a soundboard is to make it thicker or stiffer. But this make the board less compliant (less bendy) so that it has to work harder to pump air. Thus on a big, stiffly-strung harp like a pedal harp, the technique has to be quite muscularly robust in order to get a big sound out, whereas on a Paraguayan, the lightest touch produces a surprising amount of sound.
What the Dynamic Tension Balancing does is introduce a new load-bearing member to the harp. Under the soundboard, but not directly attached to it is a "spine" which acts kind of like an interior harmonic curve. Through various devises which I shan't go into here, this allows me to greatly reduce the soundboard's thickness while maintaining the necessary properties which allow it freely pump air. The result is a lighter, stronger, more compliant instrument which plays like a Celtic or Classical harp.
But wait, you also get… As I've worked with the Spine over the last while (the Butterfly has been its proving ground), I've discovered that it also produces harps that are really stable. They stay in tune. They come up to pitch quickly. The tone is consistent one to the next. And the Spine seems to help me get rid of wolf tones and other anomalies associated with laminate and plywood tops.