My experience with the CSS SDX7 - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 4 Old 12-14-2007, 03:37 PM - Thread Starter
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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 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 can get the SDX7 from for $100. I imagine they'll be available from Kyle at 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.

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post #2 of 4 Old 12-14-2007, 08:42 PM
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Thanks for the review Neil. I had emailed Bob a couple weeks ago about this driver. He got back to me super fast!
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post #3 of 4 Old 12-15-2007, 04:57 AM
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Definatly a good looking driver. I hope someone designs a project using them on htguide. I'm getting kind of bored looking at all the Dayton RS 7" woofer projects.

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post #4 of 4 Old 12-17-2007, 09:01 AM
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So these are truly a drop in replacement? I'm in the process of building a pair of Adire DDR open baffles with the Extremis, and would be interested in trying these if there is an audible improvement. The DDR's are two way, crossed at 1900hz.
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