See my article "The Columbia LP Equalization Curve" in the Spring 2009 issue of the ARSC Journal. There's a section in this article where I explain why the curve may not be at exactly +3 dB at the turnover frequency, due to the interaction of the filters for the bass and treble portions of the curve. The closer the bass and treble turnover frequencies are, the further off it can be. If you can't find this article, let me know and I'll send it to you off list.
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Dave Cawley
Sent: Friday, July 28, 2017 1:32 PM
To: [log in to unmask]
Subject: [ARSCLIST] EQ Turnover
So 500Hz turnover is +3dB at 500Hz relative to 1Khz right ?
So what is the often quoted 1,000Hz turnover measured against ? And of course 800Hz ?
It's almost time for a beer here in the UK and I can't see the wood for the trees.