Drivers & Crossover

Awhile back PE ran a clearance on some Emminence 10" Shielded woofers. They were designed as subs, but were very efficient and needed a fairly small box (~1 cu ft) to get down into low 40's or high 30's with room gain. I thought they would make an ideal starting point for the Periscope. I experimented with a variety of TM style satellites but really had nothing on hand that worked. I orginally had thought I would mount the satellites on a pole. But the wiring, sealing the boxes, and general difficulty in making the tops separable from the woofers just didn't look promising. This is the fourth iteration on this design.

Finally, I tried an MMTMM sealed column using the HiVi B3S and the Dayton ND20FB textile dome tweeter. This proved to have just enough sensitivity to match up with the Eminence woofer. This also makes it easy to detach the tower from the base, and will allow me to put the crossover inside the woofer box. I used 1/2" stock for these, but you could cut down to 3/8" easily.

I measured at 1.5 meters with microphone directly on the tweeter axis. I modeled (and measured) the HiVi's as a single driver. The ragged look of the curves accounts for some of the lobing effects from multiple drivers.

The woofer is a strange beast. It's inherent voice coil inductance of 4 mH gives it a pretty steep natural roll off, so the mids need to come in fairly low to pick up the slack. I worked quite a few hours before coming up with crossover shown below. The woofer circuit uses a single coil, with an impedance compensation (L-R-C) leg. This results in a rather broad crossover to the midrange at about 400 hz.

The midrange circuit uses a first order roll off to the woofer with a single 200uF cap. The upper roll off is also essentially first order based on the single coil. The zoebel accomplishes some shaping and phase control in the crossover to the tweeter.

The tweeter is crossed at about 4000 hZ. Though there is only a single cap, quite a bit of shaping is accomplished using the R-L network. (That resistor really exists and is necessary). Again I found that splitting the padding resistors (one before the circuit and one before the tweeter) resulted in much better phase control at the crossover.

Listening Impressions / Next Steps

With all the hassles of coming up with a usable crossover, I was pleasantly surprised. This is a well balanced speaker with tons of punch -- especially with the base against the wall. There is a slight bit of image blur on very low bass voices but the dispersion is pretty impressive. Very clear mids and nice sparkle from the tweeter. I can't say much about imaging until I get the other one built, but I'm very encouraged by the sound of the prototype. The HiVi's do a really commendable job covering the majority of the spectrum. They're a bit tricky to install, but at $10 each, I can't find much to pick at.

I have a couple of candidates for the center, the Tang Band W4-937S 4" Coaxial or possibly the W4-1320SB 4" bamboo driver. Both look like they have the sensitivity to match up. I have the coaxial in hand. It looks like it has a 2nd order LR crossover built in. It would be cool if it works out. I'll report more when I get farther along.