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Definitive Technology D9 Quasi-Anechoic Spinorama and Measurements


Major Contributor
Forum Donor
Oct 17, 2018
I decided to annoy my partner and pets - not to mention blow out my ears - and measure three speakers today. Setting up the measurement space is the worst part, so I figure I'd do it all at once.

Next is the definitive technology D9. This speaker is quite unique among mainstream speakers as it has an offset tweeter and a passive radiator. to go along with the 5-inch woofer. It seems to be available for anything from $600 to 900 in the US these days, and it comes in gloss black and white colorways with a metal front panel.


It's a classy looking design if I do say so myself. They could probably get away with selling it at a higher price for the looks and build quality. It even comes with bi-wiring binding posts which is pretty rare for the price class.

So how does it perform?

This one was a bit interesting to measure. DT doesn't specify a listening axis, but they imply toe in is optional, saying "toeing the speakers in slightly, if possible, toward your listening area will also provide a stronger center image." They don't specify a height either, so I just stuck to the tried and trusted tweeter axis, offsetting the speaker on my stand to match. 1 meter, 6.5ms gate.

Here's what we get:

D9 Spin.png

Here's the image scaled closer to what Amir uses:
D9 Squishy.jpg
Not too shabby for the price, methinks! The biggest problems appear to be:
  • Wide scoop from 1K to 3kHz in the averaged curves This mainly comes from vertical reflections, as we will later see.
  • The rather common dip/bump in the mids at ~600Hz. Unfortunately my measurements don't have too much resolution here so it's hard to know exactly how bad it is. Next time I might try simply moving the microphone closer to the speaker to see if I can examine potential resonances with more detail, even if I lose some accuracy in the overall shape of the curve.
  • A bit of a rising treble and bump at 4.5k on axis, but those disappear slightly off axis, as we'll see, suggesting the optimal listening position is indeed a slight toe-in.
Because of the offset tweeter, this speaker merits some further investigation. The speakers are specifically labeled as left and right units; in each case, the tweeter is on the outside edge of the speaker. I measured the left unit. Because the speaker is asymmetrical, I had to measure both sides horizontally.

First, here are the horizontal measurements towards the 'long' side of the tweeter:

D9 Horizontal Long.png

Hmm. That's not great. There's a large dip at 2.5kHz and bunching at 4 and 6 kHz.

But wait, there's more! Now let's see what happens on the short side of the tweeter:
D9 Horizontal Short.png

That's more like it! The directivity shows excellent control with a shorter distance to the corner of the baffle and remains wide up to about 6kHz. It's better control that we usually see from cone-and-dome systems with no substantial waveguides in this price range.

Here's the cleverness of this approach: the 'short' side is also the one nearest to your sidewall, so it is the louder and more influential of the sidewall reflections. It is likely why I was most impressed with their soundstage out of the box, despite the asymmetrical directivity. Not that Deftech is the only company to do this of course.

It's also worth noting that if you're listening off-axis these reflections should be even more similar.

Here's what it looks like in polar form:
D9 Directivity (hor) (2).png

Where things become more problematic is with the vertical measurements. You want to be listening at tweeter height, and certainly not below it:
D9 Vertical.png

And in polar form, you can see how narrow things are:
D9 Directivity (ver) (2).png

Some good, some bad, but I think mostly good. I think it's a case of a speaker that's probably better than the spin suggests. Nonetheless, that vertical is concerning and overall there seems to be lack of energy in the upper mids.
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Mar 12, 2020
thanks for the review of this original speaker.
a enthusiastic review of the D11 and a comparaison with the jbl 530 :
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