Hi!
Some time ago I purchased two pairs of IMF Compact IIs; nice little speakers but I decided to take them apart after a while ;-)
I sold the T27 tweeters off, as there is still demand for them by DIYers and people who applied too much power to their KEFs… I find them a bit harsh at higher volume.
The bass units are actually a very special kind, quite different from a standard Audax HD17B. There is much more Plastiflex on the cone & dustcap, which some people find ugly (the reason why it is reduced to a thin layer on any other Bextrene driver) but removes colouration and results in an excellent midrange performance. The voice coils are wound on aluminium carriers, not paper like in most other Audax drivers of the period. This gives them a much higher power rating; with dynamic programme like pop, rock or R&B 100 W peak power are easily handled. A powerful amp can thus compensate the low efficiency of these drivers (around 85 dB @ 2.83 V).
For a speaker that can go amazingly loud for late 70s hifi drivers AND sounds very balanced put 2 bass drivers in parallel in a 50l cabinet (you may try damped bass reflex, like the original Compact II design). In the crossover replace L1 by a low resistance I-core inductance of 50% the original value (we are at 4 Ohms now), replace the caps by a single film cap. Instead of the T27 use an Audax HD12x9D25 of the same period, to make it historically appropriate. Current Audax TW025 would be the second choice; they have higher efficiency (but less mellow sound) and will require a 1-2 Ohms resistor in series.
Use an amp with sufficient power into 4 Ohms. Mine are connected to a 1981 Yamaha A-1060, which can deliver 340 W per channel.
Stefan
Some time ago I purchased two pairs of IMF Compact IIs; nice little speakers but I decided to take them apart after a while ;-)
I sold the T27 tweeters off, as there is still demand for them by DIYers and people who applied too much power to their KEFs… I find them a bit harsh at higher volume.
The bass units are actually a very special kind, quite different from a standard Audax HD17B. There is much more Plastiflex on the cone & dustcap, which some people find ugly (the reason why it is reduced to a thin layer on any other Bextrene driver) but removes colouration and results in an excellent midrange performance. The voice coils are wound on aluminium carriers, not paper like in most other Audax drivers of the period. This gives them a much higher power rating; with dynamic programme like pop, rock or R&B 100 W peak power are easily handled. A powerful amp can thus compensate the low efficiency of these drivers (around 85 dB @ 2.83 V).
For a speaker that can go amazingly loud for late 70s hifi drivers AND sounds very balanced put 2 bass drivers in parallel in a 50l cabinet (you may try damped bass reflex, like the original Compact II design). In the crossover replace L1 by a low resistance I-core inductance of 50% the original value (we are at 4 Ohms now), replace the caps by a single film cap. Instead of the T27 use an Audax HD12x9D25 of the same period, to make it historically appropriate. Current Audax TW025 would be the second choice; they have higher efficiency (but less mellow sound) and will require a 1-2 Ohms resistor in series.
Use an amp with sufficient power into 4 Ohms. Mine are connected to a 1981 Yamaha A-1060, which can deliver 340 W per channel.
Stefan
