FR125S/SDX7 2-way

I've been working with the idea of an open-baffle full range mated with a BR woofer and came up with something that seems to work quite well.
This design uses the CSS FR125S on an OB with "wings" and the new CSS SDX7 woofer in a unique curve pipe/expansion chamber enclosure.


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I used Praxis to measure the T/S parameters of the SDX7 and came up with
Qe = .419
Qm = 2.42
Qt = .357
Fs = 33.8Hz
Vas = 29.7 L
Mms = 18.4g
Re = 6.1
BL = 7.55
Le = .75
Sd 131.8 cm^2
Xmax = 11.1 mm
SPL = 87.58 db
This led me to a total enclosure volume of 18 liter and a port size of 2" x 7.5" tuned to 38Hz.


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I decided to use a 4th order XO at about 750Hz and accepted a dip at the crossover frequency to try and minimize the effect of cancellation in the crossover range. This along with mounting the drivers close together seems to have helped. I also accepted the FR's peak at 7kHz. You can see the dip on the graph fairly easily. Neither of these anomolies are bothersome to me when listening.
The enjoyable part is the balanced sound from the mids on up rather than having a tweeter take over the upper ranges. It presents a more seamless presentation this way.


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The performance of the CSS SDX7 is almost startling in this arrangement.
Track 6 from the First Impression Music Audiophile Reference IV SACD is "Sometimes I Feel Like a Motherless Child" performed by Arne Domnerus on saxophone and Gustaf Sjokvist on a full size pipe organ recorded in the Spanga Church in Stockholm.
This track contains very low registers of the organ and this speaker plays them in a balanced manner with the rest of the music. Very impressive for a 2-way system.
The pipe behind the SDX7 is a 6" diameter plastic elbow pipe stuffed with polyester wool. The bass reflex box below it is empty except for the port tube and crossover.
The mid-range details are much improved with the FR125S being freed from the confines of a box and low frequency duties.
Thanx for that Tim... i've been playing with the SDX7 too, 14 litre sealed so far, quite amazing bottom with a 5 dB boost at 30 Hz (default on the plate i installed in the box). I have an aperiodic TL up next.

Try this. Run the pad of your finger over the cone. Now your fingernail. I can't help but think that you can hear that when the music is playing. I am on my 2nd prototype to see if i can make things better. Mail me if you'd like details (did you get my last "email")

Bob Reimer said:

Thanks for posting your project. We are certainly pleased with the performance of the SDX7 and we have some people who are now replacing their existing Extremis in 3 way designs.


My HT speakers are 3-ways using 2 Extremis, a WR125S and a Hiquphon OWIII tweeter. Swapping out the Extremis with the SDX7 would make one very impressive floorstander. In fact, I would just use 1 SDX7 per side in a TL arrangement. That would be plenty.
Love the innovative chamber.

Thanks Cal. I can't provide much in the way of emperical evidence as to why it works so well. It just seemed to make sense, in an intuitive sort of way.
My assumptions are:
1. The pipe reduces reflections back to the rear of the cone.
2. The relatively small area of the pipe provides some air mass support to the cone.
3. The stuffing in the pipe converts much of the higher frequencies to heat so mostly low frequencies are entering the lower chamber.
3. The combination of small area to large area transition, stuffing and length of the "line" is similar to a "restricted terminus quarter wave resonator" though it is a bit short to truly set up a resonance.
Another reason I wanted to use a pipe is that it provides a round surface under the OB'd driver rather than the flat surface of a box. The reflection of the sound wave off a flat surface to the rear of the speaker can be unpleasant to hear.
Timn8ter said:
Well Dave, you heard that tower of mine. The bass could get overwhelming. If the bass unit had a separate amp or pre-amp a bipole might be nice. Still, the SDX7 has a lot of output for a small woofer.

Indeed. I told the story of those on 2 consequetive days this WE :)

Still, with some people buying Apex IIIs with 4 SDX7/side it wouldn't hurt to have an option.



2004-10-26 8:44 pm
Baffle width

Most interesting -- I like the thinking!
What's the baffle width and wing depth you are working with?
How does this relate to the XO freq that you decided upon?
Given the FR125's extension, would a 1st order XO also make any sense here?
I've been thinking about embarking on an FR125 OB project, and this has gotten me thinking for sure!
FYI, here's a photo of a version of the small aperiodic boxes I did for the FR's a while back -- I keep meaning to get around to putting these up as a thread and drafting up a set of enclosure plans, but between a new start-up business and an 18mo old start-up human, those good intentions somehow keep going by the wayside....:spin:


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Timn8ter said:
I've been working with the idea of an open-baffle full range mated with a BR woofer and came up with something that seems to work quite well.
This design uses the CSS FR125S on an OB with "wings" and the new CSS SDX7 woofer in a unique curve pipe/expansion chamber enclosure.

Nice design Tim;)

So you like the SDX7 woofer :D
Compairing to the OLD Extremis I say no contest.
Cleaner tighter not a bloaty sound.Not that the Extremis was bad just this new woofer I worked with Bob on,takes the size of driver to another level.

As Dave noted Apex III with a quad of the SDX7 per speaker and 8 in a room is good.Well I think so.

So what amp you driving them with Tim?
Looks quite nice, except for the low sensitivity (SDX7 advertised as [email protected]/1m).

One thing I never really understood about these high excursion mid bass drivers is that while they are capable of producing a lot of bass for their size, they still seem to require a large cabinet in order to do so. If the cabinet size remains large, why not use a larger driver, which will no doubt have higher sensitivity?