Since the goal (IMO) is learning the basics, I think you are off to a solid start, especially considering how little information has been provided.
1. Below, say 300hz, the room will dominate your response measurements at 1m. So what you are seeing is I assume the effect of the speakers being closer to a wall/boundary. If you want to reduce that the easiest way is to stuff the port. You also want to make sure to have stuffing inside the speaker like polyfill or cotton batting or wool (I prefer wool). Adjusting all of that will impact the bass response.
2. I didn't realize you were crossing the tweeter that low. I don't think that tweeter can handle down that far. You never want to cross down to the tweeter's Fs. You want to cross no lower than double the Fs. In this case the Fs of the ND25 is 1350. So you need to be crossing no lower than 2.5k - which is what PE recommends in their specs. It's possible you may damage the tweeter if you cross that low at high volumes.
So again there are some really critical basic steps/info you are missing. I encourage you, again, to go to the PE Techtalk forum and get help there. They are really helpful to newbies and you will get a ton of responses and even crossover schematic recommendations. It's been interesting but I'm not going to offer any more help here because I think it's doing more harm than good.
I ordered stuffing, for now i filled the speaker with a sweather...
I didn't know about the correlation between Fs and crossover point ! I'll try again with that in mind. I REALLY appreciate all the help you gave me ! I think i'll try to find some "speaker building for dummies" kinda book, to fill the gaps and go further but it's hard to find something in french.
Thanks again, hope to be back in no time with a new project and some more knowledge !
