While I am not using it as my main horn at present, for some years I mainly played a Paxman 25A horn (for example on my Canto and Les Adieux CDs). It is a big horn and it is “dual bore.”
What they did with this model is make the F side bigger than normal. The photos with this article tell the tale. The slide on the left is the first valve B-flat horn slide and the slide on the right the first valve F horn slide. The B-flat horn slide is normal sized for how horns are typically made, and the F horn slide is bigger, full half inch tubing!
My Paxman model 83 triple is also dual bore but the dual part is that the high F side is smaller than standard. This gives the high F side a bit tighter feel, which is a nice adjustment on this design as well. I understand Paxman has made triples with an enlarged low F side as well. The goal is to better match the resistance of the different sides of the horn.
This type of horn, with multiple bores through the valves, can only be made by a maker that can produce their own valve sections. Most if not all of the small individual makers who sell Geyer style horns actually purchase their valves from a third party. All of the companies who mass produce horns for more of a school and student market make their own valves. And then we get to a small number of makers in a middle category, such as Paxman, makers that have enough production to support the expense of all that equipment and precision machining to produce their own valves.
So you may wonder, why dual bore? My first perceptions of old Paxman horns when I tried them years ago was that they were a bit stuffy at the bottom and this horn, with the dual bore feature, is not. They describe it on their website at present as follows:
In all the years that Paxman have been manufacturing horns, it has been our constant endeavour to respond to the needs and wishes of players. This has led us to the introduction of the dual-bore system, which is perhaps the most important innovation since the advent of the double horn almost a century ago.
When playing the standard double horns that have existed since 1898 it was, and still is, necessary to adjust to the differing acoustical resistance which is inherent in the differing lengths of the cylindrical portion of the tubing.
Paxman have developed the dual-bore system as a solution to this problem. We have enlarged the diameter of all the F-basso cylindrical tubing, and slightly modified the layout to incorporate this feature. The result of these changes has been a considerable reduction in the resistance of the F horn, matching it to the Bb side of the instrument.
I bought it in a time frame when I needed to replace my very tired old 8D and this horn served me well but it is really a big horn. I was told even by one mentor famous for using big horns that it was too big. And, backing up a step, Paxman makes a lot of models of horn. This bell is the largest they produce today; most of their production is of horns with smaller bells than my 25A.
For sure this type of horn will “speak” to some buyers. I still like the horn, but for my main instrument I have gone to the direction of a lighter, custom Geyer style horn. Myself, if I were a small maker building custom horns, I doubt that I would go to all the trouble of working out the dual bore horn when there are more standard designs that are in demand. But if you have the chance, check this type of horn out, it does have a bit of a different feel that can’t be described easily in words.