A couple of months ago, completely without seeing this thread, I did what some posters in this thread and elsewhere has been tip-toeing around, but never seemed to actually do: I put a mirror image second order crossover on the woofer of my Nova 7B's.
I use these speakers in my living room for 2-channel stereo and 5.1 video and multichannel music use. For a center channel I had been using a Pioneer SP-BS21LR. The Pioneer worked for that purpose but the tonal difference was obvious even with AVR DSP. So I've been looking for another single or pair of Nova 7B's to use one as a center channel. While looking, it seemed like a good time to experiment with putting a crossover on the woofers.
I used the same values as the tweeters, wired for use on the woofers. Got the parts from Parts-Express, and assembled the crossovers appropriately. (1mh coil in line with the + woofer terminal, 15mfd cap across the + and - of the woofer, and reversed the + and - on the tweeters as should be done on a second order filter.)
Discussion of woofer impedance and Zobel networks aside, the results have been nothing short of amazing. Previously, while the speakers sounded very good with just an upgraded cap on the tweeters, (I did that over 15 years ago and used Solen 400V caps) with a true crossover on the woofers, the clarity in the mids is better by an order of magnitude. The imaging is also greatly upgraded with a much more solid phantom center (the most notable and dramatic improvement) and a bigger soundstage "spread" with the speakers "disappearing" much more than before on appropriate recordings, despite the diffraction nightmare of the deep inset baffle and molded plastic grille. Differences in masterings between the same material is much more apparent.
And I finally found a pair of 7B's on Craigslist for a great price a few weeks ago! I modded those speakers as well. Now I have a matching center channel speaker and it has done wonders for improving the sound for 5.1 duty. Dialogue and lateral pans now sound of a whole though almost certainly because of the baffle and grille, the center channel doesn't seem to "float" like it did with the Pioneer. The sound is always coming from the speaker. Maybe the totally new crossover needs to break in more. (I did the other pair about three months before the ones I just got.) I'll have to see.
It was an incredibly worthwhile upgrade. I can only imagine what completing Tim D's work might offer for even better results. It's a shame I am not able to do that, otherwise I would.
Random notes:
1. Before the mod, when moving my head up and down, one could hear the sound change due to interference of the two tweeters with each other as well as between the tweeters and the woofer. But this is a common phenomenon with vertically inline speakers so it never really bothered me too much, and the upgraded crossover doesn't really change that.
What always
did bother me though was the change in sound when moving my head
horizontally while in my sweet spot. I assume this was a consequence of the woofers being run full range and the 12dB crossover on the tweeters. Putting a crossover on the woofer dramatically lowered this "horizontal distortion". I can move my head side to side without the sound changing character much at all now. (It does change some, but that's probably the lobing interference with the two tweeters and diffraction from the baffle/grille, I'm guessing.)
2. The speakers sound just slightly "thinner" (or maybe it could be called less mid-heavy) than before and maybe a tad less efficient, which would be logical since the woofer is no longer contributing considerable output past the 1325Hz crossover point for the tweeters. This thinness though makes them sound tonally more like my Paradigm Studio Reference 100v3's in my main setup and the ATC SCM150ASL's in my studio at work. Not a bad thing!!
3. Did I mention the incredible improvement in the phantom center channel? The 7B's after the original cap upgrade on the tweeter always had what I thought was surprisingly good imaging especially given that baffle and grille. But now...seriously...it almost sounds like the center channel speaker is in use when listening in 2-channel. That's how solid it sounds. Which is weird...I didn't expect that. The sweet spot has expanded as well. Sitting off-center on the couch doesn't have the center imaging collapse as badly as before.
4. One of the Nova 7B's I got from Craigslist had dead tweeters according to the seller. That was okay with me since I really only wanted one for a center channel but after benching the "broken" one I found out the tweeters were fine, it was the cap in the crossover that had gone blooey at some point. That makes me wonder if some of the blown tweeters people talk about in this model were actually issues with the cap in the crossover. Or maybe I was just incredibly lucky!
5. Now...maybe I'll look for a pair of Nova 6's for use as my surround speakers and get 'em all "in the family."
6. I now have one extra fully modded 7B. Lord knows what I will do with it.
