sjb@apple.com (Seth J. Bradley) (09/17/90)
Here's my design again (with a new source for the woofer, Zalytron. Zalytron is having the complete Precision line jobbered for them, and claim functional equivalence with the old line). About all I can say about the design is most everyone who has heard it has liked it. It can also be built without the equalizer (fourth order) entailing a larger cabinet and higher cutoff frequency. If anyone is interested, I'll post dimensions. Dick Pierce, who used to be chief engineer at Precison before they folded, said that the TA305F was unique among 12" drivers, and I tend to agree. I have no idea as to whether the Swan 305 is an equivalent. One final note, the accompanying schematic is for the equalizer, not a crossover. If there's any interest I can post a crossover design, but these are readily available in Jung's "Audio IC Op-Amp Applications" or through Audio Amateur/Speaker Builder. I'd recommend no higher than 100Hz. at 12dB/oct. First, the speaker itself. The driver is the Precision TA305F available for $45 from Zalytron Industries Corp., 469 Jericho Turnpike, Mineola, NY, 11501, (516) 747-3515. The inside box dimensions, viewed from the front, are: 17 3/4" Width, 28 7/8" Height and 10 7/8" Depth. The Port is 3" I.D. with a length of of 8 5/16" from the front of the baffle. The cabinet should be made of 3/4" - 1" material, well braced. The interior should be lined with acoustic fiberglass. Two good books are "How to Build Speaker Enclosures" from Radio Shack, and the book that Madisound sells, I can't recall the title. Madisound, 8608 University Green, BOX 4283, Madison, WI 53711, (608) 831-3433. The equalizer consists of a 12 dB/oct. high pass filter with an F3 of 33 Hz and a Q of 2. The circuit I use is sketched below: R3 R4 ---/\/\/-------0---------/\/\/--------| | | | __|__ | 0 +15V | ___ | | | _ | | \ | | | | \ | |-----| - \ | | \--------0-----------O Output | / | O------| |------0------| |-----0-----| + / | Input C1 | C2 | | / | | | | / | | / / | | \ \ 0 -15V | R1 / R2 / | \ \ | | __|__ | | ___ | | _ | |_____________________________________| R1, R2 22 K OHM, 1/4 W R3 1 K OHM, 1/4 W R4 1500 OHM, 1/4 W C1, C2 .22 uF OP-AMP Any audio grade op-amp, I like the Analog Devices AD712 and the Signetics NE5535, both duals. The resistors should be metal film and the capacitors audio grade, such as polypropylene. The power supply should be dual-tracking regulated, and the whole built in a metal enclosure. Jung's "Audio IC Op-Amp Applications" is a good book for construction tecniques, and includes schematics for crossovers. That's about it for the basic plans, again feel free to get back to me for more info. -- Seth J. Bradley Path: {uunet}!iwarp.intel.com!dalek!sjb