I listened to an NPR segment on this subject. They explained two things that make this wood very special in the making of instruments.
First, it dates back to a time when there was a great deal of old growth, hence the annular rings were very close together. In other words it was dense and tight ringed. Todays lumber is a result of farming practices and because it is grown in the open (as opposed to under the canopy of the surrounding forests), it's growth rings are farther apart.
Second, because of the time in the water and cold temperature, the cells have hollowed out, in effect producing sound chambers. This, combined with the fact that there are more of them due to the tight rings, create a wood for fiddles and guitars that has extreme resonance and sound.
Then, on a car radio, the moderator plucked a string on a violin. Up until this point I was mildly interested, but when he plucked that string and the note just kept sounding..........on a car radio..........and the clarity was amazing to say the least. I cannot describe to you the wonderful sound and the sustain. I told myself right then that if I get a chance to own one of the guitars made with this wood, I would give it VERY strong consideration. I can't wait to try one of these.