Subjective
I wonder if somebody at Memphis Car Audio read my last few 6x9 reviews — this set seems almost custom ordered. As mentioned in those reviews, if you like your soundstage to the rear, reflected off a large piece of glass, complete with flabby midbass and poor low-frequency extension, then by all means buy some cheap 6 x 9s and slap them in the rear deck. It won’t matter all that much which ones you buy, the effect of the speaker location will most likely make the best speaker sound as bad as the worst. However, if you’re looking for something that resembles realistic reproduction and don’t mind trying something unusual, consider a set of 6x9s in kick pods. I’m not sure if anyone makes a pre-fab kick pod for this type of speaker, but don’t let some sales guy convince you that it’s a bad idea because he doesn’t have one.

So, we have a set of 6 x 9s that appear to be a great candidate for kick panel installation, the next question to be answered is one of sound quality. Someone evidently spent a little quality time during the design of the 15-ST69s because overall, they sound quite good. They do seem to have a bit of high-frequency rise and there’s something a little weird in the upper midrange, but it’s certainly nothing that can’t be cured with a good EQ and a little patience. The upper midrange error isn’t even all that noticeable; in fact, its audibility seems highly program dependent. It didn’t really jump out at me until I auditioned the piano/violin piece on the IASCA competition CD. This track is a real litmus test for midrange accuracy and I’ve not heard a speaker system other than our ref monitors that does it justice since this CD was released.

The 15-ST69s bi-ampable nature allowed a quick comparison between performance with the stock passive tweeter filter and an external active crossover. When bi-amped, the 15-ST69’s overall midrange response was just a tad smoother but the upper mid problem was still apparent, so it must be something inherent to the tweeters response. Again, it will be easily fixed with the EQ that you’re going to need if you intend to build a serious system. All in all, these midrange gripes seem awfully nit picky for a set of 6x9s, but you know I’ve got to do it, if only for the reason that the 15-ST69s are the most impressive set of 6x9s that I’ve seen to date. We always pick on the ones that we love the most.

Objective
Impedance measurements for the 15-ST69s show a maximum of 9.5 ohms at 90 Hz and a minimum of 3.1 ohms at 11 kHz. One-watt at one-meter sensitivity measured 87.5 dB with 200 Hz to 5 kHz band-limited pink noise. Both RTA and semi-anechoic measurements show a relatively even, if not completely flat, response. RTA response shows the system’s behavior in a highly reflective environment while semi-anechoic measurements represent the system’s response devoid of reflections. The increased high frequency resolution of the semi-anechoic measurement reveals a somewhat more jagged response. The most notable response aberration appears to be a narrow but substantial dip in the tweeter’s response at about 7 kHz. The system’s in-line tweeter filter has a measured roll-off rate of about 12 dB-per-octave and a 3 dB down point of 6.4 kHz.