IMF stands for "Irving M. Fried", after the guy who designed and the speakers. His nickname was “Bud”. IMF Electronics went out of business in the late 80's. TDL was the successor company of IMF and run by most of the same people. TDL also eventually went under. There is a new company called "IMF Audio" that bought the name, but the speakers are nothing of the sort. Bud Fried was one of the greatest speaker designers who ever lived; he died a few years ago.
The speakers you saw were manufactured between 1977 and 1983. All of IMF designs were based on the "transmission line" theory. Very different from bass reflex or any other designs you might see today. The basic principal is to use smaller drivers for accuracy and space with engineered cabinets to gain frequency response with higher levels. Many of the designs also incorporate phase shifting switches on the crossovers. The transmission line theory has never been fully developed because it’s so complex. IMF and TDL probably had the best designs.
IMF’s are hard to find vintage speakers. Do you know if you saw the "ALS40" or "ALS40II Studio"? They look the same but are radically different. ALS40’s are a compact smaller breed of IMF's, but great for near field monitoring. The ALS40’s are more abundant on the used market then some other better models. They used an 8" bextrene bass unit, 8" bextrene sub-bass unit, 4" rolled surround impregnated cone mid-range with domed tweeter. The dome tweeter was probably made by Coles. Cabinets were generally very high quality. I think part of the reason they went out of business is because the speakers where made without cost in mind.
I use a pair of IMF “Studio Monitors”, they are one of a kind. If anyone is still using them today, like me, I would venture a guess that they have had new crossovers custom made. The originals were good at the time but new ones can make those speakers sound unbelievably good. A funny thing is that Bud didn’t think the quality of wiring was an important factor in acoustics, he actually said that. Bottom line is that their great.
Anyway, I could write a huge book about this so I’ll just stop here. If you want to know more visit this link or just ask, I’ll be happy to talk more! And thanks for the great post! I don't run into many people who have ever even herd of IMF, let alone actually using them in a studio.
http://imf-electronics.com/ There are a couple of factual errors I noticed on this site but you’ll find a lot of useful info including dates and timelines, frequency charts, parts that were used, crossovers, history, interviews... If this stuff interests you click on links at the bottom, they will guide you to other great websites of transmission line interest.
There is also a discussion group on yahoo called “imf-electronics”
