I know that there are a number of Stephens / Tru-Sonic fans here, so I’m hoping someone has taken some measurements or run across data sheets that I have not located. Right now I’m interested in the pure compression drivers, not the 5Kt bullet tweeters.
Recently, I found a very rare and early Stephens 108 Alnico compression driver for a ridiculously low price, which I bought knowing that it didn’t have a diaphragm. Since getting the driver in hand, I’ve taken some measurements in order to explore possible replacements. Every Stephens or Tru-Sonic compression driver that I’ve seen, including the dual concentric drivers, uses the same style of diaphragm: a spun or stamped aluminum diaphragm with a 1/2 roll flex suspension stamped outside of the edge of the dome (presumably between the outside a tall black Bakelite mounting ring/spacer to which a pair of JBL style spring binding posts are mounted on opposite sides, and a metal disc cap stamped with three stiffening ribs. Early versions like the 108 had a diamond-shaped Stephens logo glued to the center of the cap. Compared to the JBL 175 or Altec 802, the Stephens has a small 1-1/2” pole piece, with the outer diameter of the VC gap about 1-9/16” in diameter, leaving a VC cap of about 1/32”.
I’ve managed to find some old Stephens catalog pages which indicate that the Stephens compression driver voice coils used edge-wound wire like JBL, though I have not found anything regarding composition of that wire, the gauge of the wire, the material of the VC former, and the exact inner and outer diameters of the voice coil. Nor have I been able to find measurements on the depth of the dome spun/stamped into the diaphragm.
First off, does anyone have any loose Stephens/Tru-Sonic diaphragms (dead or alive) laying around that they could measure, or a compression driver or concentric on the shelf that you wouldn’t mind removing the driver to measure, or have measurements taken previously?
Second, does anyone know of any other compression driver diaphragms, hopefully high quality, with the same size voice coil?
Web photo illustrating 108s with installed diaphragms and covers:
Recently, I found a very rare and early Stephens 108 Alnico compression driver for a ridiculously low price, which I bought knowing that it didn’t have a diaphragm. Since getting the driver in hand, I’ve taken some measurements in order to explore possible replacements. Every Stephens or Tru-Sonic compression driver that I’ve seen, including the dual concentric drivers, uses the same style of diaphragm: a spun or stamped aluminum diaphragm with a 1/2 roll flex suspension stamped outside of the edge of the dome (presumably between the outside a tall black Bakelite mounting ring/spacer to which a pair of JBL style spring binding posts are mounted on opposite sides, and a metal disc cap stamped with three stiffening ribs. Early versions like the 108 had a diamond-shaped Stephens logo glued to the center of the cap. Compared to the JBL 175 or Altec 802, the Stephens has a small 1-1/2” pole piece, with the outer diameter of the VC gap about 1-9/16” in diameter, leaving a VC cap of about 1/32”.
I’ve managed to find some old Stephens catalog pages which indicate that the Stephens compression driver voice coils used edge-wound wire like JBL, though I have not found anything regarding composition of that wire, the gauge of the wire, the material of the VC former, and the exact inner and outer diameters of the voice coil. Nor have I been able to find measurements on the depth of the dome spun/stamped into the diaphragm.
First off, does anyone have any loose Stephens/Tru-Sonic diaphragms (dead or alive) laying around that they could measure, or a compression driver or concentric on the shelf that you wouldn’t mind removing the driver to measure, or have measurements taken previously?
Second, does anyone know of any other compression driver diaphragms, hopefully high quality, with the same size voice coil?
Web photo illustrating 108s with installed diaphragms and covers: