There seems to be a general agreement among harp players that “concert” spacing of strings it desired. However, since there is no absolute definition assigned to the term “concert spacing,” this leaves us with more questions than answers. About the only finite solution for the harp buyer is to ask each maker what their definition of the term might be. Otherwise, one has no sure way of knowing what to expect, except that spacing stated as “concert,” hopefully means that it is not too narrow.
The string spacing of most lever and pedal harps is graduated. That is, it may begin at about 15 to 17 mm, string center to string center, in the bass octave, but gradually diminish to as little a s13 to 14 mm in the highest register. This means that we can expect to find a center-to-center spacing of around 14.5 to 16 mm at middle C. Anything less than about 14 mm at middle C is generally perceived to be too narrow, while spacing greater than 16 mm is usually thought to be too wide.
Our Blevins harp models have an average spacing at middle C of 14.5 to 15.5 mm, measured center-to-center. Our experience with harps over the many years leads us to believe this is about what most players are comfortable with, and probably what they would call “concert” spacing. But again, there is no finite book definition of this term. When we also consider that the size of the hands and fingers of each player are different, it is not too difficult to realize why string spacing becomes an important factor when choosing a harp.
Another minor point of confusion is that while we may classify a harp as being nylon or gut strung, it must be kept in mind that most lever floor harps, while said to be nylon strung, actually can have up to 7 or more wire strings in the bass octave. We classify our Encore and Espre floor harps as being nylon strung, but these models have 6 wire core strings in the bass octave. Some models have more, some less, but the point is that virtually all makers of floor-size harps use some wire strings in the bass octaves. It is the same for the gut-strung pedal harps. This becomes necessary because good tension and string energy can only be obtained by the use of wire in the lower bass frequencies. In the low bass octave, nylon becomes little more than a big rubber band, having little tension and very low energy. The higher tension of wire is desired and almost always used in the bass octaves for harps of 30 or more strings.