Funny, that shirt. When the twin hose Mistral was phased out in the late 60's, followed by the Aquamaster a few years later, the conventional wisdom was that double hose regs would henceforth be valued on its scrap metal value. Now, some 30+ years later, divers who were not alive then are showing interest in these devices for their cache or cult value. At that time, I never dreamed of the internet and would not have even understood what was to come even if it were explained to me. Now, this new technology has infiltrated the nooks and crannies of our minds making it possible to buy, sell and popularize these old, mellow regulators among a newly risen group of aficionados. Perhaps because of my age I have always seen the double hose as a working tool, not a work of art. Yet, who can deny the luster surrounding that big hunk of chrome brass. If one looks hard enough, the image that faintly reflects back to the eye seems vagely familiar, like deja vu.
I looked at the Dan and Linda Website. There is a thread which presents some diagrams published by Bill Barada in 1962 which purport to show the relevant and respective breathing characteristics the two main types of reg, the single and double hose. Unfortunately, noone has stepped in to update this oversimplified theory. Bill did not take into account that the breathing response of the 2 hose in respect to the relative position of the mouthpiece to the regulator body, AS WELL AS the position of the diver's chest relative to the box. For example, when the diver is vertical, the mouthpiece is higher than the box (and the chest). In this instance, the vacuum required to operate the diaphragm is zero since there is already positive pressure at the mouthpiece. If one doubts, the test is to remove the mouthpiece and observe the air gurgling out. So, the breathing effort in vertical is not "neutral",and as the breathing effort in the inverted position is the reverse, and also not "neutral" as Barada suggested so many years ago.
Continuing on some previous remarks. The double hose is designed to work best when the regulator box presses against the divers back. This is accomplished by using a twin tank set with tanks no larger than 6.75 inches diameter, and NO BACKPACK. The Navy 5 point harness system is the way to go. If a pack is used, then the tanks should be no larger than 5.5 inches in diameter. Tanks in that size range can be used to make doubles and triples but the doubles work best. Unfortunately, there is no standard manifold or bands which allow the tighter spacing which these tanks could afford. They could be custom made but the logical configuration for the tanks would be twin 70's or twin 38's in their various permutations.
