good 3-4 mid range

And that is an excellent deal.  Thanks for the lead.  I'm building a new center channel for the home theatre setup and these might be fun to play with.  Think they'd match up in an MTM configuration with a Bohlender-Graebener ribbon tweeter crissed at about 3800 Hz?  I was going to try a set of Revelators...

Actually those 4's are a full range driver.  I'm sure they would work great, but I think maybe a better choice for you would be the new 6" Extremis drivers we have on pre-order (sorry for pushing our stuff, but I really think this would work best for you).  They are fully video shielded and have 12mm of linear throw (XBL^2 too).  The advantage the 4's have is their extreme upper end extention (18 kHz on axis).  And although they do have a good low end extention, our 6's will cream them.  I think matched up with the ribbons you would have a killer center channel.  Although one problem you might run into is the impedance.  Our 6's only come in 8 ohms right now, while the CSS 4's are offered in both 8 and 16 ohms.  So unless your amp can handle a 4 ohm load, the 6's might pose a problem.  Just keep that in mind.

Steven Kephart

Adire Audio

Thanks for the feedback, Steven.  I'll look at your 6's although the enclosure is already mostly ready with 4.5's in mind (and I'm not opposed to building my Xover for 16 ohms on the low end.  Plenty of power available from my Sunfire amp... in fact, it may be capable of handling 4 ohms, I'll look into that.)

stevdart, dipole surrounds are fine, especially if you use older Dolby ProLogic surround gear.  But if you are using more modern surround systems (like Dolby Digital or AC3 or any of the THX schemes) your rear surrounds have discrete program material and should really not be dipole.  Indeed, I prefer the sound of 2-way direct radiators to the diffuse dipole sound.  Besides, getting a crossover right for dipoles can be a real pain...

Ya, I do have an older Yamaha Dolby ProLogic amp, and the rears get 20 watts each at 8 ohms.  I just want to replace the crappy bose speakers I'm now using with something I make to complement  the look of the main towers.  But I know 20 watts isn't much to work with...looking ahead at Wintertime projects.

I might try something with two of these Vifa buyouts for each rear

Nice amp.  I am very jealous then.  With the 4's you have the option of 8 or 16 ohm IIRC.  So you have a lot of wiring options available.  And I'm sure you would be fine with the 4's to.  They are an incredible speaker.  You would just have more low end with the 6's, which is good for a center channel as it produces so much of what you hear. 

I am going to use the 4's in the alignment shown on their site (.25 cubes tuned to 50 Hz).  They have some pretty impressive low end in that setup.  I'd recomend a similar alignment for you if you have the enclosure space.

Steven Kephart

Adire Audio

Yea I saw those.  Vifa makes very nice drivers and those could be a steal.  Hell, at that price it's very worth trying and a nice 2-way standard or dipole surround with those could sound good in your system.

If you go for dipoles, the trick in the crossover is to wire the two woofers out of phase with each other, and to add a high-pass filter one of them at around 250 Hz so the other will produce meaningful bass.  For best effect, build them as a mirrored pair and make sure the high-passed woofer in each speaker will face the same direction.  I like side-firing dipoles with the high-passed woofer facing forward (towards the screen.)