I think DavidF hit it. The
Kef R300 are a larger 3-way speaker with 6.5" (165mm) bass drivers, and a combination 125mm (5") Mid/Tweeter and obviously in a larger cabinet.
Hi-Fi Speakers - R Series - Fact Sheets - Bookshelf - R300 - KEF United Kingdom
Frequency range (-6dB): . . . 42Hz - 45kHz
Frequency response (±3dB): 50Hz - 28kHz
Contrast that with the
Kef LS50 with a single 5" bass driver -
Flagship Hi-Fi Speakers - LS50 - Overview - KEF United Kingdom
Flagship Hi-Fi Speakers - LS50 - Fact Sheet - LS50 - LS50 - KEF United Kingdom
Frequency range (-6dB): . . . 47Hz - 45kHz
Frequency response (±3dB): 79Hz - 28kHz
A very noticeable difference in low end response.
However, the -6db rating is not that different.
The
LS50 is going to have a long slow roll off, and softer more balanced bass.
The
R300 is going to go deeper and drop off more sharply, and is likely to have more noticeable bass.
Keep in mind that a 6.5" speaker is about TWICE as big as a 5" speaker.
The
LS50 has a more sophisticated Cabinet design with the front face rolling away from the driver. Internally very well braced.
The
R300 is more of a standard Box speaker.
As a generalization, I would expect the LS50 to excel in a Surround System, though many people use them as primary music speakers. I would expect the R300 to better stand on its own as a Music speaker in a Stereo system. Though again, that's a very fine line.
Of course, the best you can do is actually listen to the speakers.
I would say that in a modest sized room with tolerable acoustics, the LS50 would make a very impressive Surround Sound system, and do a pretty fair job for music as well.
Keep in mind, it is not as simply as
this Front speaker vs that Front speaker. If you get the R300, you are somewhat committed to getting the
Kef R200C Center speakers, which is not a pixie of a speaker, nor is it cheap -
KEF R200C Centre Speaker - Superfi
Where as with the LS50, you simply need another single LS50 for the Center (£400).
Just a few thoughts.
Steve/bluewizard