The JBL enclosures were replaced with a pair of 24 liter Woodstyle WS803REV cabinets with clear oak finish. I chose sealed over vented for a little cleaner lowend. The F3 for a vented box would have been 52 hz, but I choose to accept the 66 hz F3 of the sealed simply because it sounded more natural and accurate. The vented had only marginally louder bass but was thicker and less defined. The inside back and both sides of the cabinet are completely covered with one layer of a material called Soundoff, which is similar to Dynamat. The enclosures are also lined with eggcrate foam (supplied by a dense foam mattress pad) and the open space in the middle is loosely filled with speaker fiberglass from Radio Shack. I also installed a brace made of a 1"x2" piece of MDF to go across the baffle behind the juncture of the woofer and tweeter. I figure this would strengthen and reinforce the baffle with the drivers mounted so close together. It's just glued and held in place with a single sheetrock screw which in
concealed behind the drivers.
The series crossover only has five parts and consists of an 8.2 uf cap across the woofer and a .68 mH choke across the tweeter with a 3 ohm padding resistor for the tweeter. A 7.5 ohm/22 uf cap Zobel on the woofer complete the design.
The drivers are sealed and screwed onto the baffles. The crossovers were built on two small boards which are glued over the access hole on the back of the box.
I was looking for a medium sized,
stand-mounted speaker system, capable of reproducing music as close to accurately as possible for the money/resources. This was done entirely by ear, which is why it took so long, nearly a year. I have no idea how they measure as far a "flat" response, but I do know they sound great and very musical. Very balanced, if not a little bass shy on rock or dance music. Acoustic music/instruments sound just right. With a sub, they would definitely be full range, both frequency range and dynamic range. Guess I have a new future project. The midrange performance is outstanding for an 8" woofer and the tweeter seems to have no problem with the low-ish, first order crossover. It's not that there's no bass, it's just not all that powerful. In-room, the response is into the high 30's with swept test tones. I figure F10 is around 35 hz as it bumps the needle on my RS SPL meter at -6 db @38 hz. Fb is around 52 hz on the PE Woofer Tester and Qtc is .6 with system imdedance at 6 ohms.
As for the sound, I have to retract a bit of the critique of the bass. It's excellent and does go quite low and full after all. A sub still would help but I'm not in a hurry. I'm especially pleased with the crossover and the countless hours tweaking parts values by ear paid off.
The M21 is an amazing woofer. A combination of clean, tight bass and excellent mids is hard to find. Dennis Murphy got away with 3khz second order with his DIY2000 towers. I like this woofer because it has the mids of a 6.5" without the power compression. The SEAS 27TFFC is just amazing as well. I hear no problems with the first order crossover after nearly three weeks of listening. This tweeter is very quick and contributes to the woofers punch.
I think the only problem is the fact that I have little or no baffle step comp and as a result there is a mild, broad peak around 400 to 800 hz. It's really harmless though as below that they get some reinforcement from the floor so it's really not a problem. BTW they're about 12" off the floor on cinder blocks (fool proof speaker stands) tilted back around 5 - 10 degress and about two feet from the rear wall. I live in an A-frame so the back wall slopes slightly toward the center of the room. I used Paul Verdone's diffraction spreadsheet to help determine driver placement on the baffle.
Considering these can be built for around $350, I can find few faults. I invite anyone to try them and you might just like them, too. The poly cone Vifa P21 could probably be substituted with no other changes necessary. It's very similar to the M21 but I prefer paper...
Thanks to all who have helped out or encouraged me (whether knowingly or unknowingly) during various parts of this design over the last six months: Andy Graddon, Clayton Oxendine, Dennis Murphy, Paul V., Vince Corpuz, John K., PC, PEPaul, Gordon Waters, RonO. and several other Pauls and Jeffs. And John K. whose site and study of series crossovers is what got me started on them in the first place. I'd also like to thank God, Bud, Henry and Edgar, and Bud.
