I'll just stick to the frequency response curves for now..
First of a frequency response curve measures the speakers out (SPL) for a constant amplitude signal but whose frequency is swept across the audio bandwidth, 20 Hz to 20 KHz. The flatter the curve between 20HZ and 20 Khz, the more neutral the speaker sounds. If a speaker is reported to sound bright, then there is an emphasis in the high frequency part of the speaker. That means it plays the highs louder than the rest of the frequencies. If a speaker is reported to sound dark, then the high frequency strength is played at a lower level than say the mids or the bass. The flatter the curve, the better the speaker will sound...simplistically
An ideal speaker will produce the same level of output (spound pressure) across the entire audio spectrum for a signal of constant amplitude (strength). There is no such thing as an ideal speaker as the components making up the speakers have build tolerances that may vary, the cabinet may be structurally not rigid enough imparting its signature on the output of the speaker. There is also the cross over to consider. The cross over basically filters out the frequencies (electrically) for a given driver allowing the appropriate frequencies through to the appropriate drivers.i.e. woofers get bass, tweeters get the treble and the midrange get everything in between.
Put this all together and you have a speaker.
Now the response (sound pressure level) measured dead straight at the speaker (0 degrees) will give you the flattest frequency response. As you move off axis, ie 15 or 30 degrees off center the high frequencies usually are the ones to decrease in sound pressure. Look at chart 1 and chart 2 of the soundstage link.
Thats the real basics. I hope this helped somewhat.
