Building The DRC NOnken Surrounds 18Nov23-07Dec23

I conceived a scheme to "save the BOnken cabinet" by designing a new pair of surrounds derived from the huge prior speaker cabinet. I chose Fostex FE108NS full range 4" drivers similar to those in the DRC Onkens for these new surrounds after modeling and "simulating" possible derivative Onken cabinets and drivers. The FE108NS is the latest "new SOL (NS)" driver from Fostex; it is targeted for a back loaded horn cabinet but I can't handle that size. And I've seen the numbers/performance in a simple open baffle and these can be used in other designs. So I did...

The original SOL drivers were named for "the Sun beloved timelessly and close to our heart." These seem perfect for my need in a close setting. The drivers will do especially well in the mid-range in a wide baffle design (which I can derive from the existing BOnken cabinet. The new speakers will be new Onkens, so NOnkens.

I guess this project is "design while you saw." I peeled the BOnken felt out, cut 6" of depth out of the cabinet, and glued it back together at a depth of just 14" (vs the BOnken 20"). This was painful and it created a ton of sawdust but at least it worked. Don't try this at home kids ~ hoisting the hefty BOnken around for serious cuts was cumbersome. I only did it to employ the cabinet investment I'd already made. The reassembly along the depth is a simple butt joint but the 45mm of material along each side makes the butt sufficient with just glue, especially since eventually tops & bottoms will secure everything well. What the heck can I do with the nice Onken channel port pieces remaining?

After the assembly dried I cut it in half in the other direction. Unfortunately my table saw was shy of allowing the 17" cross cut and I had to start with a handheld Skilsaw and then tidy things up on the table saw. Yeah that 45mm of material did bend the circular saw blade at temp. Ugly, tons of sawdust, and time consuming but ultimately effective... the cut was completed as hoped. I used a jigsaw to cut new holes in each face for the new drivers. I added small front "baffle" pieces to cover up the hole where the old driver had been and even a corner to assure closure. I then reinstalled felt and new binding posts with wiring in each of the two new cabinets. I cut 4 new top/bottom pieces and secured all of them to the ends of the two speakers with screws, as I had done with the failed BOnken. Finally I installed the drivers. The NOnkens were born about 5:30pm MDT 07Dec23!

With all but finishing work to be done I measured the NOnkens. They sound "ok" and are appropriately sized for dual center channel use or surround use in the Nest Music Theater. See the not so flat sound pressure level (SPL) frequency sweep under test. While I don't like the drops at 150Hz & 900Hz, I am not going to equalize them ~ they are plenty clean full range speakers for LS/RS. A big issue though is the 1KHz-4KHz shout which is probably from baffle step issues and the poor cabinet tuning. I may yet try to physically tame that loud in the upper mids ~ some inner surfaces were undamped and my screw top assembly will allow me access for some tweaks. I am prepared to bevel the port openings but am unsure I need to do that ~ they should be ok as surrounds. Subjectively the 108NS is every bit as strong for near field listening as the 108E∑... I dropped the NOnkens in the center channel spot tonight and the front soundfield was great... I also listened to them several feet high as surrounds, just to make sure.

Finishing the NOnkens will be done in the same way as with my other NestMT speakers... sanding, true black stain, and multiple coats of poly. But that will wait for spring weather. They look odd but sound OK being crafted as a 2nd thought from a failed center channel BOnken project. I need to get the signaling right now for 5.1 channels, and hang the surrounds. And I need to likely tune the NOnkens more with EQ, damping, or other 'cause they are not great. There's a chance I will just retire the NOnken cabinets, reuse the drivers, and do something else to get to 5.1 ~ Onkens built on this circuitous route just don't have the finely tuned resistive ports that ground up Onken builds should ~ and the measurements show this both on baffle step issues and on port tuning.