I'm no expert and haven't near the experience of some of the guys around here, but I've recently been comparing my RC-10s and CA S30s and thought I'd share my thoughts. As background, my only decent speakers have been an Infinity Primus 5.1 tower w/ a home build sub setup about 5 years ago. For the past 2 years I've had an Energy RC-10 4.1 setup with an Emotiva Ultra10 sub. I have some decent headphones and also dabble in recording and producing music.
This past week i picked up a pair of Cambridge Audio S30 bookshelf's to use as Zone 2 speakers in the kitchen. Since i had them both out, i decided to compare the S30s and rC10s in 2.0 stereo using my Denon 1913's Direct mode. (No sub, full range, no Audessey, no EQ, etc). For material i used the hdtracks 2013 hirez sampler along with the 2013 (new master of some sort) 24/96 of the Eagle's Hotel California. Each pair was setup on stands, the RC10s had the tweeters at ear level, the S30s are shorter and the tweeters were a bit low so i slouched a bit on the couch. ha. There is about 12" of space between the backs of the speakers and the wall behind. Also note that without any room processing, everything I observe could simply be due to my room.
I first started by listening through the material in Direct mode with the RC-10s. Running Direct mode is quite a change from what I'm used to hearing with Audessey and the sub on. I spent a good hour listening to random music to orient my ears. I then listened through most of the material with the RC-10s a a baseline. Then i switched them out for the S30s, listened through most of the material again. Then i switched back to the RC-10s for some follow up time.
Short story: Both speakers lived up to their reputations. The RC-10s are full and middy with a rolled off high end. They're transparent and airy. The S30s are pretty much the opposite in that they're tighter and much brighter, but less full. Their imaging is sharp.
Longer story: Honestly, as soon as I turned the S30s on after the RC-10 baseline, i was like "wow". They seem much more alive in the high end, more sparkle, crispness, etc. It was like a blanket was taken off the RC-10s. Actually, it was like Audessey was turned back on. I noticed in looking at Audessey's EQ for the RC-10s that they boost a lot in the 10khz range. Now, sometimes something different or hyped sounds good because its fresh. I did notice on some songs like the Patricia Barber on the HDtracks sampler, the sibilance got a little out of hand and was a bit grating. I also noticed over time that the treble started wearing on my ears.
The mid range of both speakers is pretty great. I couldn't really tell much of a difference. Vocals sounded great, violins sounded warm and woody. All really nice.
The low end definitely goes to the RC-10s. It hard to say if they really have deeper bass extension or if just the tonal balance of the speakers as a whole, but the RC-10s are on the deep/full end while the S30s are the bright, but thinner end. Both played guitar baselines nice and tight though. Kick drums sounded fuller and punchier with the RC-10s.
I would also say that the S30s image sharper. It was easier to pinpoint where a vocalist or instrument was placed. When i switched back to the RC-10s i noticed the stage was a little more blurred.
The RC-10s also have a little more of a sense of airiness and transparency. While its close, and i'm not sure if its a function of how the tweeters are balanced, the RC-10s seem a little more like music is coming out of the air and the S30s just a little more like music coming from a good speaker.
Summary: At first i was worried when i played the S30s. They really sounded alive. They really sounded "hirez". Really crisp and clear, even my fiancee noticed right away. However they did over do the treble in places and were downright unpleasant on a couple songs. I think if the S30 could be dialed back just a bit it'd really be spot on. Also, i think the S30s are more nasally than the RC10s which i think sound flatter
It did make me realize that maybe i'm not a "laid back" speaker person as the RC-10s without processing could really use a little more sparkle up top in my opinion. Since these speakers each really represent opposite ends of the spectrum, I'm really interested in finding something in the middle.
It also made me realize how much Audessey is doing for me. Turning it on with either speaker pretty much turns them into the same middle-ground sounding speaker. Do speakers even matter?