The Definitive Technology D15 speakers were measured in free-air at a height of 4 feet at a 2-meter distance from the microphone, with the microphone raised to a 7.5’ elevation that was level with and aimed at the tweeter center. The measurements were gated at 9-milliseconds. In this time window, some resolution is lost below 400 Hz and accuracy is completely lost below 200 Hz. Measurements have been smoothed at a 1/12 octave resolution.

The above graphs depict the Definitive Technology Demand D15’s on-axis and horizontal dispersion out to a 95-degree angle in five-degree increments. Information on how to interpret these graphs can be read in Understanding Loudspeaker Review Measurements Part II. The first feature that leaps out from these graphs is just how flat the on-axis response is. This is a very nicely linear behavior on-axis.  There is a rise beginning at 15 kHz which peaks at 20 kHz, but I would wager that most buyers of the D15s could hardly hear that high, not that there is much content up there anyway. The only difference that kind of peak in the response would make is perhaps the addition of a slightly more ambient sound in some recordings. We do see that the off-axis does see a small rise above 3 kHz at angles outside of 30 degrees, and this is due to a slight directivity mismatch between the tweeter and midrange driver at further off-axis angles. However, out to 30 degrees, the linearity corresponding to the on-axis response holds. The ‘listening window’ of this speaker, i.e., the +/- 30-degree angle from on-axis, is beautifully linear.

One interesting thing to see is that the linearity holds slightly better on the inside angle of the D15s as opposed to the outside angle. As was discussed in the ‘design analysis’ section, the D15 pair have specific left and right speakers, and the differentiating feature is the mirror-imaged offset tweeter; the tweeter is mounted further out from center with respect to the left or right unit. What this means is that the dispersion between the speakers is going to be slightly better than outside the speakers. It’s not hugely better, but if you want to optimally set up your Demand speakers, pay attention to the left/right designations.

The above polar map shows the same information in the preceding graphs but depicts it in a way that can offer new insight regarding these speakers’ behavior. Instead of using individual raised lines to illustrate amplitude, polar maps use color to portray amplitude, and this allows the use of a purely angle/frequency axis perspective. The advantage of these graphs is they can let us see broader trends of the speaker’s dispersion behavior more easily. More information about interpreting this graph can be read in our article Understanding Loudspeaker Review Measurements Part II.

In this polar map, we can see that the D15s have a relatively wide dispersion speaker with good coverage out to 60-degrees off-axis and within that angle directivity is fairly well controlled, although not perfectly. We more clearly see the asymmetry caused by the offset tweeter in the polar map above its crossover frequency of 2.5 kHz (in this map, the right side of the speaker is positive degree angles so left side is negative degree angles).

The above graph shows the D15’s low-frequency response captured using groundplane measurements (where the speaker and microphone are on the ground at a 2-meter distance in a wide-open area). We can see that the D15’s have a fairly flat bass response down to just below 40 Hz. Definitive Technology specs the response of these speakers as 39 Hz to 24 kHz, but they don’t give a window for that response. The low-end of their specs are not exaggerated, and these really do have a strong bass response down to 39 Hz. With a response this flat down to such a low frequency, boundary loading might give a substantial boost to the low frequencies, so users might get a tighter bass sound by pulling them away from walls or corners. These speakers aren’t designed to utilize boundary reinforcement like many other tower speakers that have a more gradually rolled-off low end response.

The above graphs show the electrical behavior of the D15 Towers. Definitive Technology specifies the impedance load of the D15s to be 8 ohms nominal, but I would call that a stretch. They have a 5.4 impedance minima at around 130 Hz. That is too low in a heavily used region for these to fairly claim an 8-ohm load. The phase angle in that region isn’t totally benign as well. If Definitive Technology claimed 6 ohms nominal, I wouldn’t argue, but 8 is a stretch. Nonetheless, this isn’t an extremely harsh electrical load. I wouldn’t want to run these speakers on a budget AVR amplifier, but I think midrange AVR’s should be able to handle these speakers without much trouble. I measured sensitivity at 84.7 dB for 2.83v at 1 meter which is pretty close to Definitive Technology’s spec of 85.5 dB for 1 watt at 1 meter. These aren’t very sensitive tower speakers, and they could benefit from some beefy amplification. On the other hand, I don’t think anyone buying a $3,400 tower speaker pair is going to drive them with a $200 AVR, so it’s not likely to be an issue. However, those who want super-loud headbanging speakers may want to look at higher sensitivity designs, as these will only have so much headroom, even with a monster amp.  

Conclusion

Before wrapping this review up, I will briefly go over the aspects of the D15 that I liked, and the aspects that I didn’t like, and as regular readers will know, I always start with the dislikes since I am the kind of guy who prefers the bad news first. But the good news about the bad news here is that there is very little bad news with respect to these speakers, and I think anyone who has read this far would have guessed that much. My only real nit-pick with the D15s doesn’t really concern the speakers themselves but Definitive Technology’s overly optimistic impedance spec for them. Too much of the electrical impedance of the speaker falls below 8 ohms for this to be considered an 8-ohm nominal load. However, as I said, that isn’t to say the electrical load of the D15s is bad, but rather it is just not as light of a load as Definitive Technology implies. However, this nit-pick is not a big deal, and I only even mention it just to have something to gripe about. One other thing I would say here that is not a complaint about the speaker but rather as a notice to would-be buyers is that while these speakers can get very loud, they can’t get insanely loud, and those looking to achieve THX Reference level loudness in a large room will have to look elsewhere. However, for 99.5% of home audio enthusiasts, these have more than enough headroom.

With those very minor criticisms out of the way, let’s go over the highlights of the D15s. First and foremost is the sound: these speakers sound terrific. They are tonally balanced, accurate, detailed, and deliver a marvelous soundstage. They have good bass extension down to 40 Hz and a good deal of dynamic range. The dispersion uniformity is good, if not quite perfect, and these aren’t speakers that need you to dress your room up in acoustic treatments for an optimal sound. They sounded great with every piece of music that I threw at them. The only time they complained was when I blasted them with very high levels of extremely deep bass in a movie, but that is not something I can fairly hold against a speaker of their design type, because it is not reasonable to expect them to play near-infrasonic bass at loud levels;. No speaker like this could. That is what subwoofers are for.

I can also appreciate how good looking these speakers are. As I said before, I think these could pass some high standards for aesthetic approval from other household members that many other floor standing speakers would not be able to clear. They look very nice, and while they are not cheap speakers, they look more expensive than they are. But the looks are not skin deep with the D15s, because the build quality is also very good. They feel as solid as they look. Again, not a cheap speaker, but it’s easy to identify where the money went.   

My time with the Demand D15 is my first close encounter with Definitive Technology as a speaker brand. I have heard other Definitive Technology speakers briefly in store demos, but those experiences were not extensive enough for me to form a meaningful opinion about the brand. For this reason I wasn’t quite sure what to expect from the Demand speakers. However, my time spent with the D15s has raised my esteem for Definitive Technology. They have created a truly good loudspeaker in the Demand D15s. They are a rock-solid choice for anyone shopping for speakers in this price range, and I can easily recommend them.