MDR-7506
In 1991, Sony introduced the MDR-7506; headphones marketed to audio professionals.
The MDR-7506 specifications describe a frequency response of 10 Hz to 20,000 Hz, in contrast to the MDR-V6's 5 Hz to 30,000 Hz.
Both models share the same part number for their driver, but the magnet therein is known to vary. The MDR-7506 was introduced with a samarium–cobalt magnet, as is currently used in the MDR-V6. However, at some point, the MDR-7506 switched to the slightly more powerful neodymium magnet. These changes were made without changing the driver part number.
In 1997, EQ magazine wrote, "Most people will use Sony MDR-V6 or similar headphones, such as the professional version Sony MDR-7506 or Koss Pro-4A. These Sony headphones have a reputation for loud sound and for blocking out at least some outside noise. A 2001 web audio book listed the MDR-7506 as "the industry favorite".
Read more about this topic: Sony MDR-V6