In 1934 Dr. Blackburn's close association with John Hilliard, started the chain of events that led to the Shearer Project and further.
Dr. Blackburn's initial responsibility on the Shearer Project involved design work on the new Lansing model 284 compression driver. Later he worked with Jim Lansing to modify the 284 (the driver has a 2.84" (72 mm) aluminum diaphragm and edgewound coil. It is energized by a field coil using 3.6 kg of copper wire. The phase plug uses three annular slits as opposed to the radial slit 285) design to address a perceived patent issue which resulted in the model 285. Lansing Manufacturing brought to Altec the foundation of a product line that would set industry standards. The 287 and 801 (using a 1.75" (45 mm) aluminum diaphragm, field coil and 1" (25 mm) diameter exit) compression drivers evolved into the Altec 288 (the 288 was actually a permanent magnet version of the field coil 287 with only a few refinements) and 802 (in the mid 1940's, Altec Lansing replaced the field coil with a permanent Alnico magnet structure to result in the model 802) that would be sound industry mainstays for the next half century and even longer. The Altec 288 (made use of a traditional high-frequency annular slit phasing plug driver with a 72 mm voice coil) driver speaker has been designed for paging systems of the highest quality.
Based on these early Altec models, the Kilimanjaro-Series drive units refined and manufactured by Wolf von Langa are capable to reproduce music signals with egregious ease and transparency. High frequency extension is shifted by 3000 Hz and distortion levels are reduced further. The result is an unheared clearness without any obstrusiveness. Purest core material, special shaped parts and extra strength field coils result in linear motors which move the original aluminium diaphragms nearly undistorted.
Smoothness, transparency and extension of the A284 is stunning.
Frequency response = 550 – 17,500 Hz
Power handling = 30 Watt
Impedance = 8 or 16 Ohm
Sensitivity = 105 dB @ 1W/1m
Diaphragm = aluminum dome driven by a 72 mm diameter voice coil
Flux density = up to 21,000 Gauss
Net weight = 13.5 kG
Diameter = 180 mm
Horn throat diameter = 36 mm
Mounting hole diameter = 83 mm (3)