Having been an orchestral musician for many years, I have given a great deal of attention to these problems. Now, after much experimenting, I believe I have found the solution:
The present descant double horn is to be changed in such a way that the B♭ horn (in the case of the triple: B♭ and F horn) remains unaltered — i.e. also the long, slim conical mouthpipe. One of the two change valves will be soldered onto the mouthpipe immediately behind the mouthpiece, instead of in the main valve cluster. From this valve, the alto F horn will now lead off and join the main body behind the cluster at the second change valve (see illustration).
Advantages:
a) Both horn sides have their own set of tubing, with both mouthpipes independent from each other;
b) each mouthpipe produces a sound ideally suited to the respective horn side;
c) each horn side has its own independent main tuning slide, since the valve slides are separate.
I have constructed this horn with the firm Helmuth Finke in Vlotho/Exter, while Dr. Klaus Wogram of the Acoustics Institute (P.T.B. Braunschweig) has been extremely helpful, using computer programs to assist in solving the tuning problems. I dare say that we have succeeded in constructing a horn that is very straightforward, without the conglomeration of tubing found in most other horns.