First of all, let me say I'm a big fan of Ascend. I think they make really good speakers at excellent prices, and I really like how transparent and accurate they are with their published specs, measurements, etc.
So I look at the CBM170 which seems like a fantastic bargain...not the most aesthetically beautiful speaker ever made, but fine for what it is. It measures *extremely* well according to independent 3rd party testing on soundstagenetwork. Now, a lot of us that follow this hobby closely know that on axis response is only a small part of the story...and that what makes a speaker truly great is accurate, neutral off axis response that closely resembles the on axis response. Considering this, I notice two things regarding the CBM170 and Sierra 1.
First, the CBM measurements on SSN(soundstagenetwork) match up with Ascends published measurements very closely. Their off axis response all the way out to 75 degrees is very good.
The Sierra 1 however, does not measure as good on SSN as Ascends published specs. Also the off axis and listening window do not look as good as the CBM170. Based on the measurements, it looks as though the CBM170's are likely to have better sound quality. Now, this may not apply at all to the Siearra with the RAAL upgrade. But based on SSN, I would have a *very* difficult time buying the Sierra 1 over the CBM170.
Again not trying to bash, but looking objectively at these two speakers and comparing the measurements on SSN and Ascends site, this is what I see.