The history of our experiments with breath pipe designs, prior to the current one, is long. We spent five years trying different things out and have tried most ideas at least once - they all suffer from one downside or another in use and whatever approach is used is inevitably a compromise. The current design sacrificed user configurability (ie, the ability to reshape the tube) for reliability, corrosion resistance, low noise (the noise introduced by turbulent flow in the breath stream, a thing that turns out to be a significant issue) and appearance.
If you're interested in the biggest design change between the 2.1 and 2.3 Alpha's, it was the improvements to reduce the turbulent flow noise in the sensor signal. To do this we sample the air pressure in your mouth cavity rather than the air that you're blowing through the system. This is quite complicated to achieve, and results in needing the two air pathways through the breath pipe as well as a really difficult piece of manufacturing in the mouthpiece.
I thought you might all be interested in a little summary (not complete, but the highlights) of the major design choices we experimented with prior to the current one:
Deformable single channel pipe with breath bypass restriction inside instrument
- Only useful user deformable, self supporting material that we could find is specially drawn copper tube. Can't be plated (plating flakes off on deformation) and poor corrosion resistance with saliva (possibly could be mitigated by internal epoxy coating but no research exists as to compatibility of these coatings with copper rather than the usual aluminum so this work would need to be undertaken to demonstrate longevity and user safety).
- Breath pressure restriction inside instrument is very hard to make adjustable, impossible to clean and prone to blockages with saliva.
- Physically practical breath restrictions inside the instrument result in too high a Reynolds Number and create turbulent air flow as a result, creating significant white noise in the sensor signal
- use of copper rather than aluminium that far up the instrument adds considerably to balance issues, raising the overall mass of the whole instrument considerably (by over three times the actual tube weight in fact)
Deformable single channel pipe with adjustable breath bypass restriction in mouthpiece
- The design used in the 2.1 (last pre-production version) instruments
- Breath bypass causes steady dribble of saliva down ones front
- Impossible (basic physics sadly) to make the system turbulence free, so white noise in the sensor signal. This could probably be dealt with using a different mouthpiece design, but the dribble of saliva above sent us in another direction
- Still suffers from the plating/deformation cosmetic issue - you can bend the pipe but you wreck your plating
- Still has some corrosion issues, though less significant
- Still has weight/balance impacts
Deformable co-axial pipe
- Two approaches - the coiled 'shower pipe' and deformable drawn copper
Coiled stiff shower pipe spectacularly ugly in the needed bore size and not that rigid. Serious doubts as to it's longevity after some testing - we found acceptable stiffness declined precipitously after a relatively small number of flex cycles. Deformable drawn copper - see above downsides. Also would need to be 9mm tube at least, non standard and requiring both a specialist die and a large, very wasteful production run to have made.
All the solutions involving copper pipe have finish issues - it can't be anodised and paint or plating mostly just flake off when the pipe is deformed after finishing. And very hard to make it look right with a Tau, or a Silver or Gold Alpha. Having said that we'd probably have lived with that, or found a way, if the other issues hadn't also been there.
Scaffolding framework with two flexible Tygon pipes
- This is essentially Mike's suggestion above. We spent some time looking at this. As an option it's possible. There are only three downsides, one engineering, one cost and one visual. One, it's hard to make 3 (at least, for the requisite adjustability) nice adjustable yet rigid locking joints that work well. Just hard though, not impossible, which gets to the next point, it's going to be expensive because of that, in design time, probably a number of prototype cycles with lots of testing and in the end quite a number of non standard parts to have made (I'd be surprised if the design cycle ended up costing less that £25-30K with the final item costing £200+, and that's being optimistic). The third point is much more subjective - it's going to look pretty 'steampunk' whatever one does. If you like that look (I don't mind it) that's cool, if you don't then it's not so good. For those three reasons we never got as far as pushing the button on making one.
Please don't think me negative about the idea of an adjustable breath pipe - I think it would be a great idea and have wanted exactly that all the way through the creation of the 'harps. I thought you might all be interested in the things we tried before we arrived where we are today, and if anyone at all has a bright idea how we might find a better way, or wants to have a go themselves then I'm in full support of that.
As far as I can see there are really two viable alternatives, one is the two pipe adjustable scaffolding, as Mike just suggested, the other is to do a single pipe thing and put the bypass up at the mouthpiece, possible using the existing mouthpiece but with some kind of spigot and then living with dribbling down ones front from time to time. Both of these could be made to work.
What we really need of course is some tube made from that great engineering material, Unobtainum. 0.4mm wall thickness, 7mm o/d, deformable but drawn with sufficient inbuilt stress to resist wall collapse at bend radii of down to 20mm. Oh, and totally inert, can be polished or anodised and doesn't cost the earth.
Wouldn't that be nice?
John
PS; apologies for the long post, lots of history to try and get across