Wow, great review Shady. I love the looks on the Demand towers and have been waiting for some measured frequency response specs before seriously considering purchasing them. It looks like these have just about the smoothest and flattest response I have seen, regardless of price - great job DefTech!
A couple of questions: once speakers are this accurate, should the main determining factors in deciding which to buy be preferences regarding looks, output, dispersion, and of course budget? Since I love the looks and don't have a large room, is there any good reason to spend significantly more than the $3200 these cost?
Also, the Demand D9 bookshelf (with similar 5.25 mid drivers) can be found for less than $500 per pair - if one already has subwoofers, would the D9's provide similar performance at a fraction of the price of the D15's, or is there some special sauce in the towers that warrants the large price difference?
I would say after accuracy, in the realm of performance, you should be looking at what kind of dynamic range you want and what kind of dispersion pattern you want. So how loud do you like to listen? If you intend to crank the system, you are going to want capable speakers. That may call for tower speakers rather than bookshelf speakers. Then look at what kind of dispersion pattern you are interested in. If you want a precise soundstage. maybe narrower dispersions are your cup of tea. If you want a wider and more enveloping soundstage, I would be looking at wide dispersion speakers.
As for looks, that is an entirely subjective matter that everyone has to weigh or themselves. It may be that another household member will not tolerate a huge unsightly speaker, in which case you are forced to spend big bucks for a pretty speaker.
As for the Demand bookshelf speakers, I don't know. There was a big gap in time between the release of the bookshelf speakers and these tower speakers, so maybe some design goals changed. The only measurement I can find for any of the Demand bookshelf speaker is
here. It looks OK but not perfect. We are doing some looking into dialogue intelligibility issues in audio, and what has been found is that dips in the 2.5 to 3kHz region can adversely impact dialogue intelligibility. Well, that speaker has a broad dip right smack dab in that region. That region is where human hearing is most sensitive, by the way, and when we see voicing like that, it can be efforts by the designers to temper content there where just a slight elevation can cause something to sound a bit harsh. However, I would prefer total neutrality if it can be achieved. If a recording sucks, it isn't the job of the loudspeaker is correct it. If you want to adjust the system sound to suit your tastes, you should use an equalizer or tone control.
I can't tell you if the D15's are worth the premium over the D9s. I can tell you that if you want your speakers to get loud, you should consider getting towers over bookshelf speakers, even if you plan to use subs.