Found!!! The lost JVC RC-M90 Panfuretto (Brochure)

⬤周波数特性図 = Frequency Response Diagram
ウーファー = Woofer
ツィーター = Tweeter
I can't read the axes, but they are obviously (y) some sort of power or volume (in dB) and (x) frequency (in Hz)
This made the frequency numbers readable though, which are 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000 and I can't read the last one.

 

I believe 17,000 is just what the tape head is capable of reproducing (with a Metal tape). But the amp and speakers should be capable of going higher.

 

Now all I need are ears that go up to 17,000Hz!