| Well, a range of mono EQ curves (and only Mono) had turnovers other than 500Hz (AES with 400Hz comes to mind, often used by Rudy van Gelder and then there was Decca with a different turnover each year in the 1950's!). |
AMR's PH-77 also adjusts the middle turnover for such curves. It is quite audible. Lest I am totally mistaken, the FM Acoustic Phonostage with adjustable EQ also adjusts this.