Quite a few manufacturers went for this during the mid to late 70s (Grundig, Siemens, 3A, Cabasse, KM, Esart...) with Philips leading the way and even advertising its MFB sets on the Japanese market until 1980...
However, at 480,000¥ (more than a Marantz Tt 1000 with an SME-3009 !), I wonder how many pairs of RH545 Philips really expected to sell...
The Philips RH545 was available as a Radiola 545 as well.
MFB (Motional Feed Back) stacks the amps right in the speaker with a piezo-electric detector and NFB loop for the bass driver to prevent distortion.
An active box of the better kind :)
I believe Luxman first patented such a system in the mid 60s, with or without Matsushita. Or Matsushita first. Or both together.
Maybe they didn't do much with it and finally licensed it ? Or was it an ever-oh-so-slightly different patent ?
It's an old thing anyway :
Voigt and Hanna patented some in 1924,
Trouton in 1928,
H.F. Olson wrote about it in 1940,
then Boer and Schenkel (1948),
Werner and Carell (RCA labs, 1957),
Brette and Perrin (1961),
Sakamoto for Matsushita in 1965... and, no doubt, plenty of others :)
Nevertheless, the RH545 is an excellent loudspeaker : tight, linear, powerful.