It's definitely both, but the single most important variable that looms above all others as far as impact on the speaker's sound is good old frequency response. Sure, distortion, radiation pattern (which has relevance to off-axis response), break-up resonances, etc are all important. But the one thing that matters most is frequency response. It doesn't matter if its a beryllium driver, a soft dome cloth tweeter, a Heil AMT, a ribbon, or a resonating Snickers bar- it's all about frequency response first, second and third. Although I found the sound of the Q7 bright as I have said previously, I don't think that is a function of the tweeter material (nor the amplifier, as has been suggested elsewhere). Rather it is simply the designer's choice to voice the speaker that way. To my ears, it had an extended but too elevated top end frequency response- but that is the designer's call. I agree with the comments made regularly by Robert Greene of TAS (the veritable REG, as he is known) who says that the most common problem he often hears in hi end audio systems is an exaggerated top end. I appreciate that it is the designer's choice in how he voices his loudspeaker, but I am in agreement with REG. Many speakers have an exaggerated top end and this is simply not a characteristic that would typically be used to characterize the sound of live music. I believe it is very often the one quality that can render the sound of one loudspeaker as "hi-fi" sounding as opposed to "musical" sounding.