# DUAL SDX 15's VERSUS XXX 18



## Ricci

I posted this over at another site and thought that it may be of interest here too.

I decided to compare my pair of SDX 15's in an 8cu ft enclosure to a XXX 18 in my ghetto 10cu ft sealed test box since I already had the 18 in the same room trying to detemine my room gain. Nothing too serious. Just for fun and what not. Thought maybe it'd be of interest.

I've been listening to the SDX's for months now and I don't have any complaints about them. The drivers are built nice and the cone looks great. The enclosure they are in is gorgeous, etc. They sound clean and well controlled with music and they will rock out a big bass fest movie pretty well. I've never heard anything bad out of them with actual material. I usually watch movies at -15 to -8 with them and that's nice and loud. This week I've moved the SDX's out of the way and replaced them with my ugly sealed XXX 18 box.

I tried to listen to a variety of different things from music, to TV, bass movies and everything in between. I didn't do anything when switching them other than roughly calibrating the two to the same level. For strictly music listening they sound pretty comparable. I think the slight edge may go to the SDX's here but I'm going from memory so it's hard to say. The XXX seemed to be a little quieter in the upper bass than the SDX's if that makes sense. It's hard to explain. Not tubby or one notey in the least, just different. Could be due to more cone area and most likely more sensitivity in the upper bass for the 2 15's? Like I said I didn't put too much thought into this. I've watched most of Rush: Live in Rio with both and on the 18 it was great just like on the
SDX's. It did seem like Neil's kick drum and toms were deeper than I remembered though. That's basically how I'd break it down the SDX's seemed more punchy and the XXX more extended and deeper. It'd be a close call and I'm not sure which I favor. I think I'd lean slightly toward the pair of SDX's for purely music.


With movies the big 18 just sounded meaner to me. The SDX 15's are fine like I said, I have no complaints with them at all and they handle loud movies quite well. The 18 just felt more tactile than I remember the 15's being with Monster House (I'd just watched it Saturday with my son) and also with Transformers. I'm going off of memory though so I could be hallucinating. (sidenote: I watched Vampire Hunter D, the japanese anime film, on DVD and there was a retarded amount of bass it seemed to me. It does not have the dynamic range of todays well produced movies, so it's compressed and all of the bass is LOUD. I noted some deep stuff in there too. If you're into that kind of thing maybe check it out.) I give movies to the XXX. It made it seem more like the room was going to collapse from alien weaponry and marauding, giant, house monsters than the SDX's do.


I put the boxes in the same spot as close as possible anyway. The SDX's are arranged vertically in a tall sonotube like deal, both front firing. The XXX is much more of a squat endtable type deal and was lower to the ground and out in the room a bit more.

The SDX's roll off below 35hz-40hz. The XXX extends much deeper and flatter more like 25hz before roll off. I know this from modeling and measurements I've taken of both. I really like both of them. It's just interesting noteing the differences and strengths of each. I've taken some measurements of the XXX and SDX's. Almost forgot the amp is the same Crown CE4000 for both.

Following are some measurements for the FR, THD and max sweep levels. A few things of note. The XXX should have a slight advantage in power from the CE4000 because it a roughly 4.5ohm minimum load and the amp is bridged into it. The SDX's are nominal 4.3ohm loads each. Shouldn't be much though since the power rating from Crown is only a 400w difference between 8ohm 2400w and 4ohm bridged 2800w. The amp runs out of gas before any of the drivers get in serious trouble. Both the SDX's and the XXX could use even more at 30hz and above for peaks. The XXX will handle a bit more power at 20hz and below but it's not going to help anything because it will have greatly increasing distortion. It is working VERY hard at the lowest freq's at the maximum spl's.

The only point where there did seem to be any serious distress from the drivers was with the SDX's at 20hz-25hz. During the THD tests there were some noticeable clacking sounds (driver excursion was high)and I'm not sure whether it was the drivers reaching the end of their rope or heavy amp clipping. I would tend to lean towards clipping but the clip lights weren't even flashing on the amp and I have run both CE4000's so hard that they have protected or shutdown many times trying to determine system limits and never heard a noise like that :scratchhead:. I would think that if that was the sound of the amp clipping I would've encountered it before with a XXX, but I never have. At 16, 12.5 and 10hz I could drive the SDX''s all the way to the onset of amp clipping with no such bad noises other than normal surround noise and distortions encountered during high excursion levels.

The FR's shown below are the maximum level right before either the amp clipped or the drivers sounded heavily distressed during the sweep. The SDX's are the red line and the XXX is the green one. Note the much more extended response of the XXX and the quicker roll off and stronger upper bass of the SDX's.


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## Ricci

I won the SDX's and the enclosure in a contest at HTS. All I did was pick what I wanted and Funkywaves Audio did the rest. 












The 18" driver is an RE Audio XXX 18d2. 











It's in a really rough box that I built with a removable baffle.


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## Ricci

Here are the THD readings I got for 63, 50, 40, 31.5, 25, 20, 16, 12.5 and 10hz. Unfortunately it appears that I did not save the results for the XXX at 50 and 63hz, or I'm unable to locate them :sad2:. I do remember that they were a few db lower than the SDX's but otherwise unremarkable. The SDX's don't break 10% until 25hz and the XXX until 20hz. This is maximum output for the systems . 

SDX's at 63hz 1.7% THD










SDX's at 50hz 1.3% THD










SDX's at 40hz 1.7% THD










XXX 18 at 40 hz 3.3% THD











SDX's at 31.5hz 5.8% THD










XXX 18 at 31.5hz 9.3% THD


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## Ricci

SDX's at 25hz 17.7% THD (Any higher level than this elicited the clacking noise described above).










XXX 18 at 25hz 10.8% THD 










SDX's at 25hz with 10% THD limit (7.2% )










SDX's at 20hz 25.5% THD (Any higher level than this elicited the clacking noise described above).










XXX 18 at 20hz 31% THD










XXX 18 at 20hz 20.5% THD










SDX's at 20hz with 10% THD limit (10.5%)









XXX 18 at 20hz with a 10%THD limit (10.8%)


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## Ricci

SDX's at 16hz 9% THD










XXX 18 at 16hz 9.3% THD









XXX 18 at 16hz 30% THD










SDX's at 12.5hz 26% THD










XXX 18 at 12.5hz 23.3% THD










XXX 18 at 12.5hz 37% THD 










SDX's at 12.5hz 10% THD limit (10.4%)










XXX 18 at 12.5hz 10% THD limit (10.8%)










SDX's at 10hz 17.1% THD









XXX 18 at 10hz 32% THD









SDX's at 10hz 10% THD limit (10.1%)










XXX 18 at 10hz 10% THD limit (10.2%)


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## Ricci

The XXX 18 has a 3.5 to 6db advantage in maximum output in these tests at all frequencies 25hz and below and a 3 to 4 db advantage in clean (10%THD limited) output below 25hz over the 2 SDX 15's. . That's some powerful displacement there. The roles reverse in the upper bass and the SDX's have superior sensitivity and output with the available power. Matches up well with what I heard in general use between the 2. Both systems should have low distortion levels and plenty of headroom with actual material useage, which also consistent with what I've been experiencing.


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## Warpdrv

Thanks for posting those measurements Ricci... Looks great.

Is it possible to take a measurement of both the drivers running at the same time... I would be curious how they complement each other, one having the upper bass superiority and the other having the bottom end... 

I plan on mixing 2 18's and 1 or 2 15's in the same room... with that idea in mind...


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## Ricci

I should've done that while I was at it. I always think of something I should've tried later on. I've already taken the XXX out of that room and put the SDX's back in the system. I guess I could at some point, but I'd have to take the XXX back in there and find a suitable spot for it. Maybe after I finish my other experiments with it. 

BTW you're running what? Isn't it going to be TC2000 15's and something else (Mal-X's?).


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## Warpdrv

Hey no problem.... Draggin that box all over has got to be a pain... 

Yes, that was my intentions.... all sealed... 2 TC2K'S and 2 Mal-X's, if I need all that, my room is 8200^3 open to everywhere...:gah:

I like to call it the suckhole for subwoofers... Dual Plus/2's just can't cut the mustard in there.... :thumbsdown:


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## Ricci

8200ft :gulp: That's a big area alright. I definitely vote that you run all 4 of them.


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