Steve Schell
03-24-2007, 02:02 AM
An Altec Lansing 287 field coil compression driver in very poor condition recently sold on ebay. It is so rusty that it may have been buried in the ground, but there are still lessons still to be learned from it:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=005&sspagename=STRK%3AMEDW%3AIT&viewitem=&item=150098085232&rd=1&rd=1
The 287 was the last of the Lansing large format field coil compression drivers that began with the 284, a driver developed in 1935 for the Shearer Horn System project at MGM studios. The 284 had a 2.84" voice coil, a three section circumferential (concentric ring) phasing plug and a 1.5" exit with threaded attachment to the horn.
The slightly later 285 driver was identical to the 284 except for a 20 slit radial phasing plug, implemented to avoid a threatened patent infringement lawsuit by Western Electric over the circumferential plug.
After the U.S. Government forced W.E. out of the business of supplying sound equipment to U.S. theatres in late 1937, Lansing reintroduced the 284 driver in a B version, with rounded die cast rear cover.
Next came the 287... apparently, as I have never seen evidence of a 286 driver. The 287 was similar to the 284B but lacked the handle of earlier drivers and used a three stud mount to the horn rather than a threaded mount. As the internal exit flare was shortened the exit diameter was now 1.4" rather than 1.5". I have seen a 287 with Lansing metal badge, so the model evidently predated the formation of Altec Lansing Corporation in late 1941. There were Altec 287s with black and white decals in 1942 and 1943, and the ones with red, white and blue decals in 1944 and perhaps into 1945- the war was on, y'know. The permanent magnet 288 driver replaced the 287 in 1945, though there may have been some overlap and replacement parts for the field coil drivers were still produced by Altec for quite a few years afterward.
Looking at the pictures, it can be seen that the 287 phasing plug was assembled from machined brass sections and the iron pole piece, channels being routed out and wire inlaid with welded spots to complete the assembly. This is the hard way to make a phasing plug, and the permanent magnet 288 used die cast phasing plug sections that pressed together without machining or welding. The top plate was easily removable in the 287 and earlier field coil drivers, and a replacement diaphragm assembly included the top plate, diaphragm and rear cover. With the advent of the 288 permanent magnet structure the top plate was no longer removable, so the diaphragm assembly with integral outer ring was devised to permit easy replacement on site.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=005&sspagename=STRK%3AMEDW%3AIT&viewitem=&item=150098085232&rd=1&rd=1
The 287 was the last of the Lansing large format field coil compression drivers that began with the 284, a driver developed in 1935 for the Shearer Horn System project at MGM studios. The 284 had a 2.84" voice coil, a three section circumferential (concentric ring) phasing plug and a 1.5" exit with threaded attachment to the horn.
The slightly later 285 driver was identical to the 284 except for a 20 slit radial phasing plug, implemented to avoid a threatened patent infringement lawsuit by Western Electric over the circumferential plug.
After the U.S. Government forced W.E. out of the business of supplying sound equipment to U.S. theatres in late 1937, Lansing reintroduced the 284 driver in a B version, with rounded die cast rear cover.
Next came the 287... apparently, as I have never seen evidence of a 286 driver. The 287 was similar to the 284B but lacked the handle of earlier drivers and used a three stud mount to the horn rather than a threaded mount. As the internal exit flare was shortened the exit diameter was now 1.4" rather than 1.5". I have seen a 287 with Lansing metal badge, so the model evidently predated the formation of Altec Lansing Corporation in late 1941. There were Altec 287s with black and white decals in 1942 and 1943, and the ones with red, white and blue decals in 1944 and perhaps into 1945- the war was on, y'know. The permanent magnet 288 driver replaced the 287 in 1945, though there may have been some overlap and replacement parts for the field coil drivers were still produced by Altec for quite a few years afterward.
Looking at the pictures, it can be seen that the 287 phasing plug was assembled from machined brass sections and the iron pole piece, channels being routed out and wire inlaid with welded spots to complete the assembly. This is the hard way to make a phasing plug, and the permanent magnet 288 used die cast phasing plug sections that pressed together without machining or welding. The top plate was easily removable in the 287 and earlier field coil drivers, and a replacement diaphragm assembly included the top plate, diaphragm and rear cover. With the advent of the 288 permanent magnet structure the top plate was no longer removable, so the diaphragm assembly with integral outer ring was devised to permit easy replacement on site.