My experience with the CSS SDX7

[DevilDriver 28]

I have received a number of pm's and emails from friends and strangers alike asking to hear more about the CSS SDX7 after I wrote about them on AudioJunkies.com. Just to give you a little background, Bob from CSS sent these to me with a pair of Extremis' in the hopes that I would be able to supply some measurements for both the SDX7 and Extremis. Unfortunately, I ran out of time and haven't captured any FR, THD, IMD, etc. But what follows is my opinion based on a few excerpts from earlier posts I made.

Almost forgot...you can get the SDX7 from www.creativesound.ca for $100. I imagine they'll be available from Kyle at acoustic-visions.com in the near future as well, but I believe he's still out of town at the moment.

Pictures and full thread.

The first thing you'll notice is that though they are similar in approach (and motor topology; they both use XBL^2), they are very different. They feature very different motors, for starts. The Extremis' motor is considerably larger and utilizes a pole vent, while the SDX7 uses 8 1/8" circular vents into the gap itself.

They both feature cast aluminum baskets that appear to be from the same parts vendor. However, they are very different in terms of their design. The Extremis has very little venting except for four evenly spaced and narrow windows just above where the frame mounts to the top plate. The SDX7, on the other hand, has a very open frame with significant venting below the spider. As far as mounting is concerned, the SDX7 has six mounting points, whereas the Extremis has 4. The mounting flanges are roughly the same.

As we work our way up the speaker, the triple joints are slightly different as well. Most notably, the neck of the cone on the SDX7 has a lot more surface area where it is glued to the former. While the spider on the Extremis is of the progressive nature and smaller in diameter, the SDX7 is a linear roll spider with a larger surface area.

The SDX7 features better quality (in terms of appearance, position, and quality) gold plated terminals. The Extremis has heavier gauge lead wires that connect just above the base of the cone, while the SDX7's lead wires connect just below the triple joint.

On to the most immediately noticeable difference: the cones. The Extremis has a Polypropylene cone with a flat dustcap that gives it a very subtle and understated look. The SDX7 is the opposite approach, showing off a beautiful copper phase plug planted firmly in the middle of a woven carbon fiber cone. I haven't measured this yet, but at a glance, the SDX7 appears to have a wider roll surround as well. I haven't measured this at all yet, but the SDX7 seems to have a much lighter diaphragm which can likely be attributed to the carbon fiber cone. This could be a great way to offset the smaller motor in terms of efficiency.

Alright, so testing fell through due to time constraints, but I figured I should post my thoughts on the SDX7 directly compared to the Extremis.

First, I thought the Extremis set a pretty good standard for bass output from a 7" driver. The SDX7 meets and exceeds that standard. Not only is it capable of more output and a little more low frequency extension, it is also MUCH more detailed. It is significantly cleaner than the Extremis through a good chunk of it's bandwidth. Noise (both aerodynamic and assembly related) on the Extremis is quite high, whereas the SDX7 is very quiet.

The SDX7 does have the typical carbon fiber break-up. As I didn't collect any measurements, it's not easy to define the bandwidth over which this break-up occurs. I would estimate it to become a bit more noticeable from 1.5 kHz and up. From a crossover standpoint, you could work around this with a sufficiently low crossover point (as long as your tweeter can get down that far) or utilizing a notch filter to tame the break-up.

Bob Reimer of CSS mentioned in email the other day that part of the reason he is marketing the SDX7 as a drop-in for the Extremis is a small dip in FR around 800 Hz. I found some female vocals to be a bit subdued, but I admit that I didn't find this that noticeable. Maybe that's just my ears but I hope not.

Build quality is also much better than on the Extremis. There is more attention to detail on the SDX7 and the manufacturing tolerances seem to be much more stringent. Where there were very wide variances in thiele/small parameters on the Extremis (when compared against the manufacturers specifications and when compared against each other), the SDX7 was spot on with both drivers.

Overall, I would rate the SDX7 as a MUCH better driver than the Extremis, particularly for the midbass and bass section. The articulate bass this 7" driver is capable of is quite impressive, in my opinion. It is being mentioned primarily as the bottom octave driver in a 3 way design (and will be available in a few 3 way kits in the near future) but I believe it is quite workable in a 2 way design with the right crossover in place.

I do hope, in the very near future, to build an OB MTM using two SDX7's and a FR125. Now that would be a rocking good time.

[flakko 1]

sweet man...are they coming out with a 5"? i coulda sworn they were...or i guess they dont need that with the fr125

[ANeonRider 3]

They won't need a 5" with the WR125 & FR125 drivers

[DevilDriver 28]

Bob is in the development stages of about 5 different drivers right now and several different kits, but I don't believe there are any plans for a 5" in the immediate future. The FR125 has been perhaps Bob's most successful products and he has several kits built around that driver...I don't believe they will make a 5" that could be closely compared to the FR125.

[Supa_c 1]

Bah, I need to go to CSS and see what kind of goodies they've got there.

Its not that far from me either.

[Tirefryr 1,742]

Thank you Neil! I was just about to PM you and ask about these when I saw this thread.

[Megalomaniac 0]

2-way out of the question with these?

[DevilDriver 28]

Not at all. For example, Occam Audio is now selling the MTM 7 using two of these:

http://occamaudio.com/Products.html

The lower the Fs on the tweeter you're using and the higher the order of the high-pass section of your crossover, the better your satisfaction will be. You can contour response a bit as well if you'd like but it's not completely necessary. I believe there have been a couple of projects on DIYAudio using these (one from a guy named Timn8ter or something to that effect that is really well done).

I will have the Occam MTM 7's in my possession in the relatively near future and can comment further on it's performance at that time.

[Megalomaniac 0]

they all look like 3 ways? am i misreading?

[DevilDriver 28]

They are MTM's. Meaning the first "way" is the tweeter and the second "way" is a pair of mids on opposite sides of the tweeter. Still a two way as the tweeter handles one group of frequencies while the two mids share another group of frequencies.

They would be three ways if each speaker handled different bandwidth.

[Megalomaniac 0]

Neil, I have a set of ID CD1 mini pros on the way i plan to cross them at 1k. You say the sdx7 is decent from 7-800 on down. will i see a big spike if run them from 50-1k? Eq should help?

[Megalomaniac 0]

bump for neil plz

[DevilDriver 28]

Neil, I have a set of ID CD1 mini pros on the way i plan to cross them at 1k. You say the sdx7 is decent from 7-800 on down. will i see a big spike if run them from 50-1k? Eq should help?

The challenge is efficiency. The SDX7's low(er) efficiency (compared to the CD1's) makes it a very poor match at the crossover frequency. While the SDX7's throw makes for a lot of output at low frequenices, the throw is of almost no advantage up top where excursion is very minimal and efficiency really takes over. You would have to dump a ton of power into the SDX7's to approach the output the CD1's are capable of in that range. You could run the SDX7's up there without much of a problem, particularly if you've got some EQ to use if necessary (really necessary for any driver in any car) but they will be a tough match with horns.

This is why you typically see 8" high efficiency drivers paired with horns...because they really are an easier match.

[Megalomaniac 0]

even if i starve the horns? what your recommendations? for a different driver with killer midbass without going 4way

[DevilDriver 28]

even if i starve the horns? what your recommendations? for a different driver with killer midbass without going 4way

You would really have to starve the horns and I'm not sure that would make having horns worthwhile. If you did a pair of SDX7's per channel or more, you would be fine. It would become more manageable if you push your high-pass crossover point lower (and increase the slope) but you're running out of bandwidth on those mini's pretty quickly at that point.

Honestly, people spend forever looking for a driver that will pair with a horn easily in a car. In pro audio, it's simple because you do a 10"+ efficient driver in a large enclosure and you're good. But it's a lot harder in a vehicle.

I'd take a look at some of the drivers people have used before. There are a few pro audio drivers that have been used before and one in particular that Jason Winslow and a few others thought highly of...might have been B&C but I can't remember. If I do, I'll let you know.

[Megalomaniac 0]

i'll stick with my hertz mids for right now to pair up with horns.

[///M5 2,833]

Going to have the same problem with those. How much space for a driver do you have?

[Megalomaniac 0]

space for a 6.5". but i dont mind do some glass work being i have 2 gallons of resin just sitting here :/