Less than a minute spent on Google found this on Music Radar:

For these D3 models, the onboard Clasts AB bi-amplification has been upgraded, now delivering 60 Watts and 40 Watts to the LF and HF units respectively; the crossover is now set at 2.5kHz (rather than 3kHz on the Carbon); and the front baffle has had a makeover. The two-part design retains the familiar M-Audio styling, with a rubberised feel to the speaker surround section. There’s an improved tweeter waveguide providing broader dispersion for a wider listening sweet spot.

When we tried the last BX5 Carbon model, we felt it was a bit too full in the low mids, but this isn’t the case with the D3, which is good news. Even so, the bass port still delivers somewhat hyped lower frequencies, and even with a good half a metre between the rear port and the back wall, we had to go for the -2dB Acoustic Space setting. In fact, we’d say the Flat setting should be reserved solely for circumstances where you have the monitors free standing in an open space.

Looking back at our notes for the BX5 Carbon, we reckon the D3 sound smoother in the top end. Yes, they are still bright and lack any form of HF tweak, which is a shame. We didn’t find them particularly fatiguing, though, and we think that the new waveguide does help deliver a broad sweet spot.

Stephen, post: 465227, member: 52024 wrote: are they both good for professional mixing and mastering atleast for small room pad

They should be ok for mixing, but not for mastering. Mastering is an art that ask far more than cheap monitors.. ;)

Unless you have a perfect room and wonderful equipment, it finishes with the mix. In fact I'm not even sure that nowadays, mastering is even a separate process in a single one place project. I see a value in taking a product as good as you can get elsewhere to improve it, but so much of what people now call mastering isn't - it's just remixing and polishing. In my humble view it's the audio version of the video/movie colorists job. Something that needs Grade 1 monitors, properly aligned and suitable brightness levels. I'm a poor colourist, and I suspect my mastering ears are compromised too.

Stephen, post: 465227, member: 52024 wrote: Please I need help for this.....(I'm about buying an M audio monitor but what's the difference between Bx5 carbon and Bx5 d3....and are they both good for professional mixing and mastering atleast for small room pad....thank you

They should be ok for s first set of speakers. They are not really aimed at professionals, tho monitors are fairly subjective, and alot of pro's use the modesr KRK rokits.

You will need to treat your room with lots of bass trapping, and some mid/ high absorbers for the speakers to work as intended.