Sarang, the smaller the +/- db spec on the speaker, the more linear, or 'accurate' it is over the listed freq range....+/-3db is more linear than +/-6db for instance, but not as linear as +/-2db over the same range. So the +/- 3db is the variation from 34hz to 20khz(at 34hz it's down -3db) where at a lower 25hz starting point the speaker is down -9db....ie the freq response is quite flat down to 34hz then it tapers off at an increasing rate(that's where a sub is handy).
I wouldn't worry too much about the ohm ratings as long as you have one of the brands known to work well with a 4ohm load. Most modern mid level avr's should be fine. Keep in mind, a lot of speakers which are listed as being 8ohm speakers(considered easier to drive) actually have dips much, much lower into the 4 ohm region as well.
The X-over points are where each driver(woofer/mid/tweeter) takes over a certain set of freq's which they were designed for. The points where these drivers are crossed over, depends on a number of factors but mainly to do with the drivers themselves. For instance, some woofers are quite able to be crossed over at up to and over 2000khz, but you're asking the drivers to play a broad range that might be better played by two drivers covering different frequencies.
I hope that helps a little. Maybe one of the engineery guys can elaborate.
Last edited by Adrian; 03/03/11 03:39 PM. Reason: Doggone it! could have saved myself a whole lot of typing if I knew Chris was answering....
