Fullrange Single Driver Tower Speakers by Greg Monfort



These were built for a friend whose hearing above 10kHz is gone so no super tweeter is used (nor the polyfil filter due to his room/location), though I highly recommend adding one. Also, mounting the driver from the rear with the front of the baffle opening radiused in lieu of front mounted/rear beveled if the rather unsightly polyfil filter isn't used.

Radio Shack 40-1354 modded by trimming off the gasket flush with the metal frame lip, 3/4" thick polyfil stuffed between cone/whizzer and held in place with a rubberband, epoxied magnet assembly to the frame, added a foil star to the center of the dustcap (much good natured wise-cracking over this), damped the frame with gutter/drain/roof foil backed repair tape, used resilient caulk to install 3/4" polyfil squares to the inside of the frame legs, and added thinned rubber cement on bell lip of the whizzer after softening them with my fingers.

Cabs are made from planed down planks (0.62") from a 150+yr old barn, and hard as nails, so no stiffeners were used. This helped immensely with maintaining some semblance of tonal balance from LF to HF. Inside dims (i.d.) are 47.88" h x 6.93" w x 5.69" d.. Drivers are mirror image and 37.25" i.d. up from bottom, 3.03" i.d. over, with the 2" i.d. dia x 2"L vent on the same vertical center and 21.31" i.d. up. Using 0.25lbs/ft^3 of R-19 fiberglass house insulation required 0.43lbs/speaker with 0.25lbs stuffed from top down to the driver, one wall and back lined with a 2" thick layer opposite it, and the balance stuffed down to just above the vent.

Since I figured they would position the speakers well away from any walls for auditioning, I used Velcro to attach an 8.13" square of 3/4" polyfil over the driver/baffle with a hole cut in it to expose just the whizzer/dustcap (a real pain to cut neatly, which I failed at). With it in place, the LAUD measurement revealed a < +/-3dB FR from 60-12kHz, with an F3 = ~40Hz. Without it, there was a ~1k-5kHz broadband peak in the response, so it is an effective acoustic notch filter in this application with minimal affect on the LF/HF. IOW, an acoustic means of baffle step compensation. The hole is to ensure that what little top octave response they have isn't attenuated.

Since these are front mounted, I beveled out the backside of the baffle opening to reduce reflections off it. I used 8-32 T-nuts and Phillips head machine screws to mount the drivers, and rope caulking for gasketing. Terminals at the bottom rear are cheap/simple screw connectors for ring tongue connectors. Wiring is 4ft of 14ga solid copper pulled from 14/2 NM-B in-wall house wire and twisted together by clamping at one end and chucking them in a drill. The stripped ends were squeezed flat in a vise and soldered at each end with 2% silver bearing solder.

I've been wondering what a decent substitute would be for the old wood I used to maintain good tonal balance, so I measured/calculated its density and it turns out that many hardwood planks could be used. If you can acquire any of these 1x8 boards planed down to 5/8" thick, then:

Hard Maple
Red Oak
Teak
White Ash (now this would be stunning)
Hard Mahogany
French Walnut


Note that the hardwoods would need to be stressed relieved (allowed to age) before using them for speaker building.

Unfortunately, RS closed out the drivers for $5 (originally $15) between the time that I built these and the competition (and consequently couldn't enter them in the budget class), so if you don't already have them good luck finding any if you want to build these.

GM

Here they are set up at the Atlanta DIY 2001 show...



Here is a shot for scale. I am the one standing and Jim Griffin is seated.