View Full Version : My experience with the CSS SDX7

12-14-2007, 12:02 PM
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 (http://www.audiojunkies.com/blog/890/css-unveils-the-sdx7-at-last-a-replacement-for-the-extremis). 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. (http://www.soundground.ca/forum/showthread.php?t=9)

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. :D

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. ;)

12-15-2007, 12:17 AM
Very interested in this driver. Thanks for sharing your thoughts on them.

12-15-2007, 12:26 AM
Good read.


12-15-2007, 01:23 PM
Any home audio purposes?

12-15-2007, 01:30 PM
I thought Dan tossed the "XBL^2" label in favor of "split-gap" when Adire went south ? Yet I notice the sticker on the magnet of the SDX states it's "XBL^2 Enabled" ?

12-15-2007, 01:40 PM
I thought Dan tossed the "XBL^2" label in favor of "split-gap" when Adire went south ? Yet I notice the sticker on the magnet of the SDX states it's "XBL^2 Enabled" ?

I thought that was what he was doing as well. Now it seems like he is dropping the "^2" part of the name. He's actually updated his site a bit.


I haven't spoken with Dan in a long time...most of my XBL correspondence is through Kevin at DIYCable/Exodus Audio and Bob at CSS.

Any home audio purposes?

Yes, lots of home audio purposes. There are some kits coming out in the near future from CSS and OccamAudio that will feature the SDX7.

And like I mentioned in pm, there is some stuff I have in the works as well.

12-15-2007, 01:44 PM
I'll keep my eyes peeled. I am looking for something with a pre-assembled crossover (or one where the pieces are already picked out) and I just do the "putting it together part".

12-15-2007, 01:56 PM
Now if someone would make a good 10 inch midbass that is relatively shallow. And works well in a door, and is cheap. And looks good and sounds good. And gets fairly loud. And blows chicks clothes off.

Good info. Looking forward to hearing what you think of them when you get to really use them.

12-16-2007, 01:57 AM
Forgot to ask, what's the mounting depth on these? From the pics they look a bit shallower than the Extremis', but it could be the angle.

12-17-2007, 01:42 AM
I want some MTMs using these. NOW!!!

Great write up. I feel in love with these drivers the moment i saw them

12-17-2007, 01:46 AM
They are really quite beautiful. There is just something about the copper phase plugs. CSS has them on the SDX7 and the FR/WR series and the Seas Excel drivers that use similar phase plugs are absolutely beautiful as well.

I really, really want to do the SDX7-FR125-SDX7 OB MTM like now, but I'm so busy. Maybe over Christmas if I'm lucky.

And there are a lot of kits coming around the corner for the SDX7, both as a drop-in replacement for the Extremis in existing kits and in brand new kits.

12-17-2007, 01:49 AM
Yea, I just finished building my budget mtm dayton stuff, painting them tomor and i want them gone so i can build these. What is this


a compact subwoofer?

Are these kits gonna come with enclosures? I really would like a high quality set of mains and a center that looks beautiful

also do you know where these are being built at? If you cant disclose it here maybe you could pm it to me. wiggins doesnt have a build house anymore does he?

12-17-2007, 01:59 AM
Yup, that's a small subwoofer kit. Quite a lot of potential in that, but I think the real beauty of these drivers will be in designs just like you suggested...good MTM's where a pair of SDX7's can give you great output in stereo to the point where a subwoofer is a bonus and not a requirement.

There are some kits that will come finished and some that come with the front baffle and all other necessary parts (except for the rest of the enclosure). For easy happiness, it is so hard to beat a DIY kit in a PE or Madisound pre-built cabinet...the amount of time those cabinets save you are well worth the price. In fact, some companies I know of have just started doing their finished kits using PE or Madisound cabinets. Word on the street is that a good buff job on the PE piano gloss curved cabinets looks like a million bucks.

The SDX7's are built in Taipei, Taiwan. Bob has always been straight forward about where his drivers are built. From what I have been told, there are no US buildhouses that do XBL^2 any more and Dan's work since Adire went down the tubes has apparently earned him very strong ties in Asia. I have had a few different XBL^2 drivers that were manufactured outside of the US that have build quality far and above what I am accustomed to. I can think of a state-side buildhouse or two that would be doing well to build as well as some of these oriental buildhouses are.

12-17-2007, 02:03 AM
Thanks for the input. I really want something that looks like that compact subwoofer they got there. I tried so hard making mine, but its just not in me to make something that looks as nice as that lol.

I was having a hard time finding where they were coming from but I guess I shouldve just asked you lol.

If you come up with any MTM designs let me know as I can't wait to get something in here :)

12-17-2007, 02:13 AM
Thanks for the input. I really want something that looks like that compact subwoofer they got there. I tried so hard making mine, but its just not in me to make something that looks as nice as that lol.

I was having a hard time finding where they were coming from but I guess I shouldve just asked you lol.

If you come up with any MTM designs let me know as I can't wait to get something in here :)

I hear you on the appearance thing. I like to think I know a thing or two about speakers but when it comes to woodworking, I can't hold a candle to what I could buy finished.

I'll let you know what happens with what. You can ask any time, too.

Oh, and Bob doesn't post in big bold letters that his drivers are made in Asia but if you ask him, he'll tell you point blank that's where they come from. And the box the drivers come in have the label on them. None of this so called "assembled" in USA stuff.

No offense, RD Audio. ;)

12-17-2007, 02:23 AM

I really dont care where things come from, as long as its quality as it appears that is. Just something i wanted to know. Since the AA poly mids are no longer made and Wiggins no longer makes anything domestically.

You should go ahead and make the design for the 2 x7s and the fr and ill build it :)