B³9 JBL high efficiency music and home theater speakers

This is my high efficiency music and home theater speakers built around classic JBL Alnico drivers. The woofer and midrange duties are handled by a somewhat obscure 15" coax driver the JBL 2150. Built in the 1970s this unit combines a woofer similar to the D130 and a centrally mounted LE5 mid/tweeter. I bought my first pair of 2150s as a lark. At the price it was a "what have I got to loose" deal. Of course when an audio maniac asks himself "what have I got to loose?" the answer is hundreds and hundreds of hours and dollars. One look at the pristine pair my seller delivered and I could see these were far beyond anything from the local hi-fi hut. One listen and I was hooked. My opinion is the combination of extreme precision manufacture, Alnico magnets, and the edge termination of the stiff suspension yields a sound combining low distortion and high dynamics the likes of which one never hears out of typical modern designs. The 2150 was really intended for PA use so the T/S parameters are a bit different. All the box design programs yielded the same result. For bass into the 30s they need a 14 cubic foot enclosure! In best audiophile rationalization mode I reasoned my previous B&W802II and Stax F81 ESLs had taken that much floor space once positioned away from the walls in audio geek approved locations. And they would be sitting next to our new Marantz 60" RPTV. So I went for it. The rationalization lasted until picking up the basic boxes from the cabinet maker. They are HUGE! Before adding the internal bracing we took a picture with both my 6 year old son and 6 foot tall me sitting completely inside the box with its removable back off!! Basic boxes are professionally built to my design and then finished by myself. A blending of modern high end enclosure design and ideas from the classic Onken I call it the B³9 JBL. This stands for Big Black Box #9 as it was the ninth revision of the CAD design. Front baffle is 2 1/4 inch thick multiply birch finished in many coats of wet sanded varnish. The rest of the enclosure is 3/4 inch MDF with extensive bracing. It is finished in a gray speckled laminate to better match the TV and withstand life. Venting is out the back panel via 8 each 2 inch diameter ports per enclosure for low air flow speeds tuning the box to 34 Hz. On top of the main system we see a JBL 375 compression driver mounted to a turned maple horn. This lovely horn is a product of Dr. Bruce Edgar's Edgarhorn company. When these pictures were taken the Edgarhorn had not yet been varnished to match the B³9. Sounds too good to take off line that long! Currently much of the capability of the Edgarhorn/375 combination goes unused. The horn is a 1k Hz cutoff design and the 375 will go even lower than that. For now they are simply functioning as a super tweeter being crossed over with a 20k 1st order HPF to add a bit of sparkle to the 2150's LE5. Future additions of more SET amps and electronic crossover will allow experimenting to tune in just how much of the midrange the LE5 should cover vs. Edgarhorn/375 horn.

B³9 JBL speaker and Doc Bottlehead S.E.X. amp which powers it. Recently a scratch built 2A3 SET amp was completed adding to the tuning options.

The B³9 JBLs at home with Marantz 60" RPTV. The grills are cut from florescent light fixture covers and were selected mainly to protect the drivers from family room traffic. As a bonus they are as acoustically transparent as they are visually. As I became ever more enamored with the 2150 I realized it fit in perfectly with my desire to combine high end audio with new found enthusiasms for triode amps and home theater. Thus I obtained four more 2150 drivers to equip a complete surround sound system. Currently four are in use, the front channels shown above and two rear channels mounted on di-pole baffles. Experiments with a center channel 2150 are part of the project queue along with bi/tri-amping.