A brief explanation.
On a 3 valve enharmonic (for example) the mouthpipe leads into the 3rd.valve. If the 3rd. valve is not used, the windway leads through into the 1st. & 2nd. valves in the normal way, and back through the 3rd. to the bell.
If the 3rd. is operated, the windway is lead through the 1st. & 2nd. valves by a different route. including a tuning slide, and in also going through different passages in the 1st. & 2nd. valves, will be directed through seperate longer loops of tubing (if the 1st. 2nd. are operated with the 3rd.).
The idea was that it is superior to the compensating system in that the windway is not required to pass through each valve more than once. Air is redirected back through on compensating loops. The obvious weight problems when you get to tubas in this range must have been enormous.
In 1913 this model retailed at £18 18 s.(old shillings).
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