Thanks for the feedback, Lou, Ron & Dave.
As long as we're on a roll, here's a link to another file that may be of interest:
This is an Excel spreadsheet to calculate the treble roll-off frequency when you know the attenuation in dB at 10 kHz. My old friend G.R. Koonce - a long-time fellow author for audioXpress magazine (and one of its predecessors called Speaker Builder) shared this with me decades ago. This is the first formula in the sidebar on p. 55.
Entering all that math into a calculator is a bit cumbersome, with all those parentheses - this makes it much easier. When G.R. sent me the formula, he took me through the various steps in the process - the results of each step are documented in the top version of the spreadsheet. This is probably only of interest to mathematicians or hard-core electrical engineers (I am neither!). The bottom version is undocumented, but gives the same result.
If you play with this and compare the results with those in Table 1 on page 41, you'll note that the spreadsheet results will differ from those in Table 1 for -13.75 dB (RIAA) and -16 dB (NAB and Columbia Lp). That's because those two were calculated directly from the time constants. If the time constants are known, using them directly will always give a more precise result. But, recording curves in the pre-RIAA era were generally defined by turnover frequencies rather than time constants. And, preamps with variable EQ almost always give the attenuation in dB at 10 k without telling you the turnover frequency.
I hope some of you find this useful. Have fun!
Audio Engineer Emeritus
The Crane School of Music
SUNY at Potsdam, NY 13676
"Great art presupposes the alert mind of the educated listener."
"A true artist doesn't want to be admired, he wants to be believed."