So they do function fine with dead or even absent surrounds but look really shabby that way and the acoustic sealing is slightly disrupted.Īs for the APM-4, the bass-reflex port is tuned very low in frequency ( < 25 Hz) so this is practically a sealed enclosure design (which is also why I like them so much).

However, given the very structure of the APM drivers, the diaphragm doesn't hang loose without surrounds as the piston movement is activated by four coils/pistons and stiffened by a centering cap/rod. The APM-77 drivers were reused in the later ESPRIT APM-4 and alas suffer the same illness as most of Sony's APMs : the bass foam surrounds rot away. The chassis are all diecast aluminium of the science-fiction-esque kind ! There's a supplementary layer of very thin damper sheet between the honeycomb and the aluminium covers. Original and shortlived version.Īs the 1980s turned out to be far more conventional than expected, it is the later 77W ( W for Wood) that is well remembered : the latter has a quality and thick veneer plus beautifully designed plywood grille frames.ĪPM drivers are made of an aluminium honeycomb mainframe with ultra-thin aluminium covers - 100x more rigid than paper cones. The 77 sported a slightly grainy grey finish and was thus quite modernistically futuristic this was however made of a cheap plastified layer glued on the enclosures.

The APM-77 is the original 'affordable' APM loudspeaker : launched after the APM-8 but before both the APM-6 and APM-4.

Sony fh 77