Sure, Beav,
With few exceptions, nearly all the closed-reed calls available use the same basic JC Products voice and most are of the single reed variety, with a single stainless steel reed. The double reed type is the same dimensions as the single, but has two stainless steel reeds, one above the other, with the topmost reed having two small dimples in it to prevent the reeds from sticking together and fouling one another. The sound they produce is more raspy than the singles. I personally, like a single jack voice more. But, I'm finishing a run of thirty new calls and would like to get a feel for what callers want in voices and if it would be worth it to invest in a quantity of these reeds in addition to the singles.