I have no idea where you got this "knowledge", but is wrong.
Sansui was even a pioneer in loudspeaker development late '70s, early '80s, especially in cone material.
Just the opinion from a person that did research the history of Sansui.
Good listening on your preferred loudspeakers!
This is common knowledge. Sorry but perhaps it is you who should get more information on how the japanese industy worked. You can read more here, to give you an idea of how the japanese industry worked:
Warning. if you think that only one japanese brand (i.e. Sansui) is superior to others, the above link will shatter your expectations.
Now, in japan, speaker drivers were manufactured by only a few companies: Coral, Fostex/Foster, Pioneer, Matsushita (Technics/Panasonic), Those manufactured for other companies as well as for themselves. Now, besides them, just a few BIG companies also made their drivers, as far as i know used only on their speakers: Sony and Diatone (Mitubishi), Yamaha: Note that Sony, Matushita, Yamaha and MItsubishi are/were absolutely HUGE companies (mitsubishi even made planes...).
Now apart from that there are the plethora of other manufacturers that were smaller and simply subcontracted many things out, to put just an example, many manufacturers -including obviously Sansui- subcontracted out turntable manufactuing to Fujiya, CEC, Micro Seiki and others. And so on with anything that is not the core business of the company. The core business of Sansui was (first) transformers and then amplifiers.
Only a few companies made many kind of devices for themselves, again, mostly the major, big companies: Sony, Matsushita. At least those two were able to make the compelte chain of audio devices without requiring subcontractors: Speakers, Amplifiers, Cassette players, Turntables. But even those two did use subcontractors on lower priced equipment, ocassionally.
Complete speakers? Coral and Pioneer were major OEMs for other manufacturers and this gets a bit more obvious when you disassemble, for example, an Akai speaker to see that the drivers were made by Coral or Fostex, but with an Akai logo stamped instead.
Now let's go for just an example of OEM subcontracting
This is on the Sansui SP-200
Now what do we have on an Akai speaker of the same vintage?
Look att the speaker basket stamp ribs, shape and holes. It's the same stamping.
This was not made by Sansui nor Akai... This is a subcontracted driver, most likely Coral.
Sansui making their own cones? Not by a long shot... this would make no business sense to them. To put things in perspective, in the 1970s Sony wanted to be the #1 speaker manufacturer and they had to invest in a huge factory only for the purposes of making speaker cones. And again note that Sony was a huge company in the 70s.
