I own two Larrivee dreadnought's the 14-fret D-40R and a SD-40RW. I find that the 14-fret instrument seems to have greater sustain while the 12-fret instrument seems to have more punch to it. I love both instruments. I was watching a video on Alverez Guitars discussing the 14 fret and 12 fret dreadnoughts. At around minute 6:50 they talk about the bridge placement saying the 14-fret instrument has more sustain because the bridge is over the X brace and the 12-fret instrument has more punch because the bridge isn't over the X brace and activates the soundboard more. Is the generally true about these versions of the dreadnought? I'll post the video below.

https://www.youtube.com/watch?v=dh7XV_8GWD8

 My experience with them is that the 12 fretters tend to have greater sustain, but a lot of this will vary depending on the build and overall quality. The closest apples to apples comparison I can make is among Larrivees I've owned. My L09 and SD60 leans toward the 09 for sustain, but the 09 has Brazilian rosewood which skewes things a bit. SD60 vs D03R (both east Indian rosewood) would have the SD leading by a wide margin in the sustain department.

"Punch" is not a well defined term, with some thinking of it as dynamic response and others describing it as low frequency response. 14 fretters generally have more "bite" to the attack, meaning a more aggressive midrange. 12 fret instruments have a bigger low frequency response. Punch can also refer to touch response and I feel this is another strength of 12 fret instruments.

Hope that perspective helps. My initial thought is that my experience would be the opposite as the video you saw. But, like I said, there's a lot of variables and ways to interpret them.

Thanks for your response. At least I know that putting the bridge over the braces isn't a rule for greater sustain. I'm considering getting a mahogany tone wood guitar. And this reopens the 12-fret instrument category. My SD-40 is pretty new and it's sustain is almost as as long as my D-40. I'm sure as it is played in this will increase. I had a Waterloo Jumbo King and it had lot sof sound and sustain except on the first string. After several months that first string just opened up and it was great. Aesthetically I prefer the proportions of a 12 fret instrument.