 Despite being up on 1" blocks a thunderstorm blew enough water into the garage to get to my box. |
Aug 29, 2008 - Page 3 Trapezoidal Baffle I set up a new trapezoid shaped baffle (TSB). Still 16" high, but evenly tapered from the bottom to about 5" at the top. I also built a new back chamber about 3" deep internally (Roughly 8 X 3 X 3 internal dimensions). This chamber is secured with screws from the front of the baffle and sealed with a bead of cured hot melt. It's stuffed with fiberglass and accoustic foam. Again I remeasured with the chamber and without it. I also went back to ground zero, and rebuilt crossovers from scratch in LspCad. I built and listened to 5 different versions of the crossovers. I tried them with and without the back chamber. The TSB definitely got rid of some of the peakiness in in the 900-1200 region. Measurement Summary Here Despite my initial efforts, there was an annoying peak at about 1200 Hz. It didn't look like much on the CAD, but it was annoying in listening at any respectably loud volume. I invited Xavier over to audition the Beta 0.9 version. He balked at the peak, and pinpointed a lack of authority in the lower midrange. ("Left hand of the piano") The design sounded a bit thin and edgy. When we put the chamber in place, the spectrum filled out and smoothed considerably. I went back and revised the crossover again, adding a notch filter for the 1200 Hz peak. I also added a series notch to the Neo 3 and relaxed the padding a bit. The final Beta 0.99 release is shown below. Not as complicated as it looks. A cap-coil cross at the low end of the mid. Coil-Cap-Coil to the tweeter. I was a bit concerned with the impedance drop at 900, but even my little Accurian amp handles these without distress. |
Impressions, Speculation and What's Next
Is the Neo8 a good midrange -- absolutely. The Neo3PDRW is marvelous as always -- it sounds good with a variety of padding and contouring options. Together, they are a seamless match - neither is pushed past it's limits. I will finish this design and may very well keep it. Now that I am committed to a chamber for the Neo8, I may redeign the box to improve aesthetics. I may try a cylindrical back chamber too.
OB is Dead to Me (at least for now)
For me, the idea of an open baffle Neo8 (with this woofer) isn't going to happen. I wanted to hear something amazing -- I didn't. I really wanted to. The omnidirectionality wasn't all that much better with OB than with the chamber. I'll take the clarity & substance over the "air". I know I'm a heretic and will burn in audiophile hell. (Bose AM radios...?) For my lifestyle, OB just doesn't seem practical. (I have visions of trying to remove gobs of bloodhound & shepherd hair from the back.) Sooo, I would really need to hear something over the top, before I'd drink the KoolAid.
I haven't heard a lot of open baffle designs. Those I have heard were not appreciably better than a well designed conventional speaker. Different yes, better is debatable. if I heard Linkwitz's Orions, in a perfectly designed room, with accoustic treatments, and $10,000+ in electronics, I'm sure I'd be impressed!
WTF? Part 2
In all the measurements, the OB looked like it went lower, and had more grunt. In listening, the chambered version was a clear aural winner. My measurements don't agree with B&G's. I'm not surprised. I guess measurements don't tell the whole story! OMG, what will all the sycophants do!?!
I just don't think the Neo8 has grunt at the bottom end. You'll notice my final design has no padding resistors on the midrange. The few people (that I've found on the net) who have done OB, have used active crossovers or multiple Neo8's. In virtually every configuration I tried, I preferred the back chamber. I think if you ran it up to 1000 or so, maybe it would work as a single. But you can push the Neo3 down to 1800 in a pinch -- so what would you really gain?
I suspect that the backwave makes it back to the microphone and enforces the spl -- but what we hear sounds more like weak echos or is somewhat cancelled coming around the edge. Linkwitz has really done a lot of investigation on this. I also think the planar design of the Neo8 may have a different effect at the microphone than it does at my ears. Most OB's are built around conventional drivers, conventional wisdom may not apply. Since I don't listen with my measurement setup, I believe my ears.
