I’m working on an issue with a chanter reed that has a narrow range of stability around back D, one suggestion made by the maker was to use a small wire rush in the bore above the back D. Easy enough to try, and it does seem to work to help stabilize the pitch.
Question I have is why does this work? The problem with this particular reed is if the back D is played with even slight underpressure, the tone goes quite sharp quickly, and with minor over pressure drops to a C. I was able to get the dropping improved by a tip sanding, but the rush seems to help stabilize the underspressure sharpening.
I’m not sure that the wire inserted in the bore above the thumb hole actually stabilizes anything. I’m guessing that in your case (assuming you’re talking about a wide bore D chanter) that the wire lowers the pitch for the thumb hole, which use to go sharp with underpressure, and the wire keeps it from going sharp by lowering the acoustic impedance.
What hapens with overpressure, when the wire is inserted, would say something too. I’d guess the back D would sink still, perhaps even easier. Too much humidity can cause a reed with thin lips to sink, or there might be a tiny air leak somewhere.
If it’s is a wide bore D chanter, a rolled staple might solve the sinking D. I have a wonderful reed with a flared brass tube staple, by the maker, that causes the back D to sink badly. Every time I replace it, with an extra copper rolled staple I have, the back D stabilizes and I can’t get it to sink. The problem is probably in my chanter, but just switching staples makes all the difference…everything else being equal.
I know a wire in the throat area can stabilize the bottom D though, but your wire prabably doesn’t go that far up…just guessing.
I have found the thicker the lips of the reed the more pressure stable it is, so I usually improve my back D stability with the cutting of “2 spider’s legs” worth of lip off rather than sanding the lips thinner.
If the chanter upper bore has been bored out too much or the wood has changed the bore with curing (I forgot what reaming that area out improves, you need to ask a pipemaker, but it should be reamed to “almost” get the aimed at note “just right”), a rush above the back D will flatten the back D and C#, make hard D easier to hit (these effects I notice in my Hillmann concert D chanter at least) and it also can change the behavior and tuning of ghost D and E and octave E.
I think there was an article in the Irish Pipers club issues in the last couple of years, I am too lazy just now to look it up for you. (damn prednisone).