misterdog
Not the canine kind
I think there may be confusion between the Quad Pro version, and the Pro upgrade offered by OTA.
From Stereophile.
The speaker's structural rigidity was increased for the launch of the ESL-63 USA Monitor in 1988. This evolved from a special "pro" version used by Philips' European recording division for location recording. Quad replaced the '63's aluminum frame with steel, and put handles on the sides and rubber kick pleats at the base. Philips was delighted, and soon other studios requested the "pro" version. Quad decided that the improved structural rigidity made it the best version for export, even though it increased the speaker's weight by 30%.
Read more at https://www.stereophile.com/content...static-loudspeaker-page-2#ieG86WQOEuLfT8Rh.99
From Stereophile.
The speaker's structural rigidity was increased for the launch of the ESL-63 USA Monitor in 1988. This evolved from a special "pro" version used by Philips' European recording division for location recording. Quad replaced the '63's aluminum frame with steel, and put handles on the sides and rubber kick pleats at the base. Philips was delighted, and soon other studios requested the "pro" version. Quad decided that the improved structural rigidity made it the best version for export, even though it increased the speaker's weight by 30%.
Read more at https://www.stereophile.com/content...static-loudspeaker-page-2#ieG86WQOEuLfT8Rh.99