IPC LU-1104 original diaphragm question

[boptura]

hi all,
i own a couple of IPC LU-1104 drivers, unfortunately only one had its original diaphragm (i personally pulled out the E5011 diaphragm when the red wax seal was still intact) so i currently run them with 21531 diaphragms (and they work very well)

the drivers are (for me) identical (same label, same paint,...) except one have ''Hollywood'' on rear cover, anyway they sound identical with the 291 diaphragms (on 311-60 horns)

some friends and altec experts told me that it is very strange that the IPC drivers could work with 291 diaphragms and that they will work much better with their original diaphragms....

which are the correct altec diaphragms for IPC drivers ? i need to replace both diaphragms or there is a corresponding altec part number to E5011 ?

thanks and sorry for my bad english....

[Jim D]

The IPC drivers (Simplex) are either 288b or c models. If they are painted with a "crinckle" paint, a plastic loading cap that connects directly above the diaphragm, and have a rope seal under the diaphragm cover they are probably Bs. If the paint is smooth, they have no loading cap, have felt padding inside the cover, and there is a rubber ring gasket under the cover they are probably Cs. If they are bs, I would be surprised that they would work well with the 291 diaphragm as the voice coil former on it, and any other later diaphragm, will bottom on the voice coil gap shorting ring which is at the bottom of the gap. To install later units you must have this ring removed, the only place is Great Plains Audio. C and later models do not have this ring and all the 288-291-299 diaphragms will work fine. I am in agreement with your friends, the 288 diaphragm will sound nicer than the ones you have. Consult the replacement diaphragm list on the site for the 288 number and your desired impedance. Jim

[boptura]

Thank you Jim,
both drivers have ''crinkle'' paint and the one with the original diaphragm have the plastic loading cap.
i measured the voice coil gap deep: approx. 4mm (0.16 inches) on both drivers, so i assume they are Bs with the magnetic shorting ring...
unfortunately i live in italy and the double shipping costs to Great Plains and return could easily reach the drivers value.
can i try myself to remove the ring, in order to use later diaphragms ? if not, how many chances can i have to found another E5011 20ohms original diaphragm ?


thanks and merry christmas!
Paolo

[Jim D]

Most of the IPC drivers I have seen have been 288Bs. If you do not play your drivers at a high level you might get away with the newer diaphragms. They attach the Voice Coil lead in wires at the bottom of the former which is farther into the gap than the older diaphragms. What happens is the ribbon wire that the voice coil attaches to sticks down and at longer excursions, hits the shorting ring and shorts out the voice coil effectively monentarily cutting out the driver. Do not try to remove the rings yourself. It will require a (de) magnetizer before dissassembly and a magnetizer after reassembly. You will also need to properly align the driver before remagnetizing. The only hope you might have is to find diaphragms out of earlier 288Cs that have the short voice coil. Do not think that all of the old 20221 units, the same ALTEC number for the 288B and C, are short, they are not. In fact even later year versions of those made on the older bakelite ring with screw terminals (pre 1980 +-) have the long VC. I was lucky, I got some used units out of early C models for my Bs when we reinstalled the Cs with new diaphragms. Maybe some other person with early Cs can help you. The C will take any of the new or old style units. JIM

[Jim D]

Oh, I forgot to tell you, the E5011 is simply the IPC number for the 20221 diaphragm and that 16 ohn units out of early 288Ds will also work. These will again be on the bakelite ring with screw terminals and be before 1970. Jim