It has been a very, very long time since I've heard the Carver ribbons. I remember their bass as being detailed and lacking any obvious boominess. However, I don't remember it being very fast, although this may have been my impression of the bass blending with the rest of the system.
My RM40s exhibit a pronounced lack of boxiness or boominess in the bass, and they are VERY fast. There's no sense that the woofers are slower than the ribbons operating the mids and highs. Of course this can't be the case, but Brian seems to work real magic getting the appparent transient response blended between the woofers and the neo-ribbons. This speed is apparent in percussion of course, but it can also be appreciated in piano, plucked guitar and violin/viola/cello strings. The best thing for me is that while the amount of bass produced can be prodigious, it doesn't seem to "overload" my room like my old Sunfire subwoofer did. This overloading was often impressive, but it wasn't "musical" and it masked details in the bass and extreme lower midrange. This wasn't strictly a subwoofer balance or blending problem with the main speakers, it seemed to be how the Sunfire subwoofer developed wavefronts in the room. It may also have been the result of the motional-feedback amplification in the subwoofer. I always thought this kind of technology (also employed by the big Infinity speakers) was ideal for bass performance, but I think my experience with the RM40S seems to support Brian Cheney's contention that motion-feedback bass circuitry can't relly react properly to the actual driver motion in time to really correct bass problems. The bass sounds big, deep and impressive but lacks detail, transient quickness and a sense of "air" imparted to even low frequencies. I know "air" isn't a term usually associated with bass, but in fact a good bass reproducing chain will impart a great deal of information about the space where a recording is made, particularly the venue's apparent size.
