ESPRIT APM-4
(1983 - 1987)

The penultimate ESPRIT component to be launched (the TA-N902 was the ultimate), the APM-4 benefitted from the research made on APM-8 prototypes circa 1982, rounding off the the top and bottom sides of the enclosures. You can see that APM-8 prototype in TVK's Invisibilia section.
As the APM-6, the enclosure is real thick bended and carved wood - NOT cheap MDF with a cool veneer added.

The APM-4 was a lighter, more domestic, version released in Europe with an "E" added: APM-4E. I don't know of any differences between the japanese APM-4 and the APM-4E... but I'd love to have a pair of them just the same.

As one japanese Sony engineer once said, APMs weren't necessarily better, they were a different way to reach the same goal as conventional dynamic loudspeakers... Often tagged as "typical Sony gadgetry", it should be noted that Sony produced far less flat-driver loudspeakers than Technics for instance.

What unfortunately prevents contemporary comparisons is that most big APMs got junked throughout the 1980s and 1990s due to incomprehensible unavailability of spare surrounds. Even more sadly, re-foaming these square drivers is a difficult feat which suffers no error.

The top image comes from a 1984 japanese ad, the one to the right from a 1983 german catalog ; the cutout view from a 1984 Stereo Sound special on the ESPRIT series. The '84 ad is btw the most beautiful ad from the set published for the ESPRIT series between 1979 and 1984.

A japanese APM-dedicated website with plenty of images right here.