[Phoca]

I'm having a hard time interpreting the AnyEQ worksheet as it gives different curves for 78s (Decca, Westrex, BSI, etc.) and provides different terms for the frequency points (e.g. pole and zero for the filter values and corner and turnover for the eq values).  Any advice on choosing one of the 78 EQ settings for 78s from, say 1920s to 1950s?  I don't know how to tell what the cutting EQ was for each.  Also, while I think I've figured out the terms for the EQ and filter values, can someone clarify for me so I understand better?  For example, what values would you enter for the Decca 78 EQ, and where would the values go?  What is the treble zero for?  Is that for cutting the treble rolloff at a specified high frequency point ala Allen Wright?

I'm considering ordering a second Bugle for my 78s (I enjoy one for my LPs) and want to make sure I understand how to adjust the components properly.

Thanks!

[poty]

There were no standards at the times. Common info about this you can find anywhere, simple explanations, for example http://en.wikipedia.org/wiki/RIAA_equalization. It means you can not build one and for all single equaliser. But the problem has several near perfect solutions, including "middle-set" equaliser and switchable approaches.
Relating the products of J. Hagermann - try to look at:
http://www.audiocircle.com/index.php?topic=10339.0
http://www.hagtech.com/pdf/monogram.pdf
http://www.audiocircle.com/index.php?topic=61180.0
http://www.audiocircle.com/index.php?topic=9354.0
to get an idea of what could be done.

[Phoca]

Thanks, Poty.  Your links led me to this one: http://www.shellac.org/wams/wequal.html, which somehow helped me to understand what's going on.  So at some low frequency, bass is boosted on playback, and that frequency varies considerably depending on the company.  Then at 10kHz, there needs to be a specific amount of rolloff which varies by company?  And that amount in turn defines where the treble "pole" needs to be under the HagTech EQ tool?  And while I can't quite figure out the formula Jim gives on the EQ page, presumably, I could use it to determine the treble turnover frequency or pole?

So, on the HagTech too, bass zero refers to the bass turnover frequency (the frequency at which bass boost needs to start) and the bass pole refers to the bass corner in Jim's reference table?  Finally, what is the bass pole or bass corner, and why won't the calculator let you enter anything less than 40Hz?  The reference data shows no value for bass corner, so I would think that would mean leaving the "bass pole" field empty in the calculator, but that can't be done.  So what to enter?

Many thanks again.

PS - my goal is to determine two curves to approximate different EQs, and build them into the two sides of the Bugle (though I have thought about trying to replicate the Bugle Pro with switchable values for the bass turnover and treble cut).

[poty]

...So at some low frequency, bass is boosted on playback, and that frequency varies considerably depending on the company.

Correct.

Then at 10kHz, there needs to be a specific amount of rolloff which varies by company?  And that amount in turn defines where the treble "pole" needs to be under the HagTech EQ tool?

Correct.

And while I can't quite figure out the formula Jim gives on the EQ page, presumably, I could use it to determine the treble turnover frequency or pole?

You don't need to use formulas to determine treble pole frequency. Jim gives you a simple plot to convert dB to kHz - look at "Figure 3. 10kHz dB-cut to frequency conversion." on the same page (AnyEQ).

... on the HagTech ... bass zero refers to the bass turnover frequency (the frequency at which bass boost needs to start) and the bass pole refers to the bass corner in Jim's reference table?

Correct. Bass Corner = Bass Pole; Bass Turnover = Bass Zero

... what is the bass pole or bass corner, and why won't the calculator let you enter anything less than 40Hz?

The idea of bass pole and bass corner is explained on Figure 2 of AnyEQ page. (TAUp corresponds to pole, TAUz - to zero). 40Hz is practical limit I think.

The reference data shows no value for bass corner, so I would think that would mean leaving the "bass pole" field empty in the calculator, but that can't be done.  So what to enter?

I think as far as you have a lot of differences even in the bass zero param you can replicate 40-50Hz value in the Bass Pole field. It won't changed the values of the EQ significantly. Several know values for Bass Pole is shown (as Bass Corner) in Reference Information below the calculator.
You can easily compare the resulting values with the Bugle Pro values to get the idea if you do all right.