To me, this is the most important MEASURABLE characteristic that I look for in a speaker. IMO, if this is not flat, you're not really hearing the true timbre of instruments. Because high-end audio is about reproducing the recording with complete honesty, the tonal response should be neutral, doesn't it? I'm not saying it's the only important design parameter, but definitely it should be the starting point, and is very basic. Unfortunately, and I wonder why, there are many ultra-expensive speakers that don't even meet this basic criterion. This is not an anti-brand post, but here's some examples: Sonus Faber Amati - it's got a problematic response-peak in the midbass Krell LAT-1 - the FR graph looks like a roller coaster ride! Krell LAT-2 - midrange response is prominent, then shelved-down below 500 Hz Wilson WP6 (and most other Wilsons) - through its many iterations, this "monitor" speaker never really achieved monitor-quality flat frequency response... its FR graphs always being rather rough. Then there's a bass lift centered at 100Hz, and above 15KHz, it's got serious dip and then peak! Why can't ALL speakers that cost above $5000 at least level with the well-behaved FR of really "honest" speakers as Revel, B&W, JMLab and Dynaudio, for example? So does all this matter to you at all?