Frequency Response

you might hear speakers' mid-range being described as "ruler flat" across a certain frequency spectrum. That basically means there are no peaks or valleys in the response that affect the lows, mids or highs. This is my understanding of what linearity is.
Be careful of specs that say "+/-6dB" in the frequency response. my Quad 22L2s are spec'd down to 30Hz, but on a +/-6dB axis. In my room, auditioned with test CDs and music, I doubt they'd rate much below 38-40Hz on a +/-3dB axis. They certainly don't produce as much bass as my cheaper monitor audio Bx5s, but I still love the Quads' soundstage and mid-range sound.
There are other things to consider besides frequency response, like sensitivity, it's important because it affects which amp you pick. Those Tannoys might be easier to drive than most.

>11-01-12: Realremo
you might hear speakers' mid-range being described as "ruler flat" across a certain frequency spectrum. That basically means there are no peaks or valleys in the response that affect the lows, mids or highs. This is my understanding of what linearity is.

This is still meaningless because our brains perceive timbre as a weighted combination of the spectra from what they believe to be a direct sound and its reflections where we expect decreased high frequency content in the delayed signals (nature absorbs and diffuses more at high frequencies because objects like grass blades and rock surfaces are becoming acoustically large) and do not perceive local maxima in spectral content vs frequency as natural sounding.

Traditional speakers with a 6-8" mid-range drivers crossed to dome tweeters around 2.5 KHz have such a maxima as they transition from the midrange that's becoming acoustically large and starting to beam to the tweeter that's acoustically small and radiating hemi-spherically regardless of how flat they are on-axis with the resulting sound being harsh in situations with nearby untreated walls and ceiling.

Designers can and do compensate for the excess off-axis energy with a notch around the cross-over point like the BBC dip which makes the speaker perceptually flatter although it no longer measures this way.

The right fix (which works in more rooms and doesn't cost you detail which comes from the direct sound level) is more driver + baffle combinations sized appropriately for the wavelengths being reproduced although that is more expensive.

>11-01-12: Drew_eckhardt
>The right fix (which works in more rooms and doesn't cost you detail which comes from the direct sound level) is more driver + baffle combinations sized appropriately for the wavelengths being reproduced although that is more expensive.

Wave guides and dipole cancellation which increase acoustically small driver directivity for a better match to the lower frequency driver are other solutions which work well.

I like a speaker to have response down to at least 40hz and 30hz is even better and high end is a non issue for me, they have all been good no matter what the spec.

more important is speaker tonal balance and if the speaker works in YOUR room.

as a general guideline I hope this helps

Linear, in this case does not mean flat.