Obviously the Alpha is the higher-level in the Infinity line, but there are a few other things you should consider:
- Because of the price-point the Primus line is far more popular than the Alpha line: matching speakers will be easier/cheaper, sharing tech support (& help on these furums) will be easier, and finding reviews online will be easier.
- While the Alphas do go lower, they are also a little less efficient and that means that it will take a little more amp power to drive them.
- Both speakers have a silver front w/o the grills. A lot of people don't like that.
- The Alphas are bi-amp capable.
- The CMMD tweeter on the Alpha is supposed to be much better, but I cannot tell the difference.
(I have a pair of Primus 150's at home that I compared to the Apha 20's and although the Alphas were only slightly more expensive, I still chose the 150's.)
I have some Alpha 50's that I auditioned along with some Beta 50's and the Primus' as well. The difference between the Alphas and Betas were minimal at best, but the differences between the Alphas and the Primus' were huge. While the Primus' sound is just fine if you use a sub or don't care too much for lower bass sounds, the Alphas sounded so much richer and capable. They do require a break in period, mine have just begun to level out now, and they sound awesome. They love to be pushed hard, and they can handle anything I throw at them. You can really crank these things, and I can detect NO hiss, or cracks, or anything, just pure, powerful sound. I highly recommend the Infinity Alpha 50's without any reservations. Also I bi-wired mine and that made a much noticable improvement.
i own the primus 150 and have been impressed with the sound these little guys throw. Smooth midrange and decent bass. When pressed they tend to break up, but that is being picky at their price. Also noticed they sound better in a larger room (could be my house). If you plan to add more speakers in the future the Primus is tops becuase of their low price and easy to timbre match across the line.
Also consider buying the 150s and adding a separate sub. This way you have much more control over the sound by controling the bass. Infinity offers some really nice subs with the RABOS system which will allow you to tune the 2.1 system to your room.