I have in my possesion an EMI 14" x 9" loudspeaker, which I've had for a good many years and fairly recently I've started using it as a sub-woofer in my workshop system (and it seems to perform well). At the moment it just sits on the bench, so its performance will be degraded by not being in a cabinet. I'm intending to build one, preferably I would like to make it a transmission line enclosure, but I need to find some more information on the unit itself first. The 14 x 9 speakers were manufactured by EMI sometime between the 1960s and 1980s and were superseded by 13 x 8 inch ones. They have a model number of 770 but this actually covers a range of speakers, some were customised for speaker manufacturers (I believe early B&W DM3s used them). I have seen several others speakers that I can't identify and that used them, They were also available as parts of speaker kits that EMI sold in this period. The speaker I have has the further marking AEP, which I guess defines the variant. It also has another number 3278 which I imagine is the serial number. The speaker has a cast aluminium chassis with a 5 inch ceramic magnet and a 2 inch voice coil. The voice coil former and inner cone is aluminium bonded to the outer cone, which is a multi-layer laminated paper with some sort fibre reinforcement and has a rolled plastic surround. The front face of the cone is coated with some sort of fur like material, which I've been advised is to reduce the effects of cone breakup. It has a DC resistance of 5 ohms.
I've tried to do some testing, but I'm not really equipped for doing this. I think I've identified the mechanical resonance as being 18Hz with a second harmonic at 36Hz, which was done by feeding it with a constant amplitude sine wave over the frequency range 10 to 150Hz and observing the cone displacement and I think I saw an increase in displacement at those frequencies, but I could be wrong.
If anyone has come across these speakers and can throw any more light on this, I would be most grateful.
Phil