The woofer is the Dayton RS180. You can use the shielded or unshielded woofer. I did some pretty thorough testing, and found out that the two perform pretty much identically with regard to a crossover.
There are two options for the tweeter: aluminum or silk dome. The two tweeters are almost drop-in replacements for one another, with only one component needing to change in the crossover to switch between the two.
The crossover is identical for the aluminum and silk-dome tweeters. The only difference is that the silk version omits capacitor C4. Prepare for the technical jargon: The woofer uses a quasi-2nd order filter with C2 acting as an elliptic notch filter, and R2 contouring the woofer's response through the midrange slightly. The tweeter filter is a simple 2nd order, and R1 pads the tweeter level down to match the woofer.
The crossover point in the Core 2-way is very low (around 1400 Hz). I did this simply because the drivers were able to, and I figured why not. The advantage of crossing the RS180 so low is that it eliminates the harsh breakup mode--for all practical purposes, anyway. Granted, with the Amiga and TRS-80, I worked very hard to squash the breakup mode, and honestly, I'm not sure it's audible in those designs, either. However, there are some who believe that metal-cone drivers should always be crossed low, period. This design would be more their style.
The Frequency Response shows a noticeable dip centered around 3 KHz,
and this is extremely normal for a tweeter centered on an 8" wide
baffle. It goes away when you listen slightly off-axis (ie: speakers
pointed straight ahead, not toed-in).
The impedance load presented by the Core should be safe for pretty much any amp. If it were a commercial loudspeaker, it would be labeled "8 Ohms nominal."
I'm very pleased with the sound. It's definitely in the same family as the other RS180 designs I've done; the advantage of the RS28 is that it has the flattest response. As for whether I prefer the RS28A or RS28F; I prefer the aluminum dome (RS28A). It's a wonderful tweeter, once you raise the top octave a bit with a mild contour filter (C4 + R1). It's super-clean and never sounds splashy or sibilant. However, this may be a matter of personal taste, and some people prefer the sound of silk-dome tweeters because they tend to sound just a bit more "airy." (Some have publicly stated that they prefer the "F" to the "A.") In that case, they should choose the slik version.
So why did I even bother with this design when there's already the amazing Modula TM? Well, let me start by saying that in no way am I trying to "outdo" that speaker--I can hardly even understand the crossover! I've heard it at DIY events, and it is very good. I'd like to think that the two designs can coexist. To my ears, the Modula sound as if they were designed with classical and other top-notch recordings in-mind, and will showcase them in full-detail. As a result, the Modula can be quite revealing of poor-quality recordings. The Core--as with most of my designs--was voiced to play well with normal, everyday recordings (Rock, Pop, etc.), which often times don't have "audiophile-grade" production values. Also, the Core is a taller, narrower speaker, where the Modula is more of a large bookshelf. Please don't think I'm trying to steal any thunder from Jon Marsh and his design. We can all live in harmony, right?
Here's Mark's humorous anecdote about how his friends and family reacted to the speakers...
Friends and Family: Wait a minute, you bought $200 worth of speakers and had them delivered to a guy in Chicago?
Me: Yes. Actually I believe it’s a suburb of Chicago.
Friends and Family: Is he friends with ****? (My Nephew who lives in Chicago.)
Friends and Family: You only know him because he posts on a forum?
Me: Well yes, but he also has his own web site.
Friends and Family: So this guy you never ever met said he would be glad to design a speaker for you for “free” if you send him $200 worth of speakers?
Me: Well no I never personally met him, but others on the forum have met him at DIY speaker events.
Friends and Family: So you have met the other forum members that have met the Chicago guy.
Me: Well so far I haven’t attended any DIY events, but some of the forum members that may have met him have over 12,000 posts.
Friends and Family: We always knew you had more money than brains but till now you were to too cheap to prove it. You aren’t also on a forum with the son of the King of Nigeria are you?
At this point I play them some music thru the Cores.
Friends and Family: Wow, those are absolutely amazing. You really need to thank that nice guy you don’t know that lives somewhere in Illinois and has a website. He is obviously a genius.
Me: Thank you Mr. Carmody.
This pair was built by [HAROLD].
Harold's comments on the speakers and cabinets:
The baffles are spalted wood I bought on Ebay. They were 32x8.5x1/4in thick.. You can find them on ebay under luthier supplies. I glued each piece to 1/2 in MDF. The rest of the the boxes are 3/4 MDF covered by paper backed cherry veneer. I really like the look. I was going to give them to a friend but they turned out so well I just can't part with them. I chose the Core 2-ways cause I didn't want to lose any more of the spalted wood than I had to.
However I had no idea they would sound as good as they do(another reason not to part with them). I have been playing them all day and can't believe the huge sound. Thanks for another great design.