Question about LT component calculation

[Greybeard191]

I've finished completion of a 4-tempest classic sub array and measured the resultant system
Fb=36hz
Q=0.6

It's actually spookily close to Unibox's predicted response for a heavily stuffed 380 liter box (Fb=35.92, Qtc-.62)

I'm playing around with two different spreadsheets for LT component calculation:

1) The True Audio's LT cct design spreadsheet (linkxfrm.xls)
2) LT shreadsheet downloadable from Linkwitz Labs (pz-eql.xls)
3) LT transform spreadsheet from the FRD consortium (linktranadv29.13.xls)

The first and second seems easiest to use... they allow for simple input of existing (tested) Fb/Qtc, input desired new Fb/Qtc (I'll use 14hz/.577 for an example), pick one capacitor value (0.047uF, left as default) and get the other 5 component values.

Problem... I tried figuring out how to get the FRD spreadsheet to verify the values, and they're not even close. The only thing comparable is the DC gain (16.41 dB from both). Using the same fixed cap as a starting point obviously.

The obvious answer is that the FRD spreadsheet isn't meant to be used this way... example, I can't MAKE the information tab give me a calculated Fb of 36hz Q=0.6, so can I really play around with the transform information in the schematics tab?

Looking for some assurance as to which method to go with. And please, no commentary on what target FB/Qtc should be... just gave those as examples

thanks

GB

[PMazz]

The obvious answer is that the FRD spreadsheet isn't meant to be used this way... example, I can't MAKE the information tab give me a calculated Fb of 36hz Q=0.6, so can I really play around with the transform information in the schematics tab?

Use the "imported" side of the box information section. You can manually enter the measured Fsc and Qtc.

Pete

[Greybeard191]

I tried that, but the information doesn't actually make it into the "transofrm information" box in the schematics tab of the workbook.

I've tried over typing both the transform information and tranform components values, and i can make it give the same poles & zeros as the other two spreadsheets by manually inputting the values of the components from the first two spreadsheets... so I'll probably use the first two spreadsheets (which match). The FRD spreadsheet seems to calculate component values differently... I got similar poles and zeros, but quite different component values.

thanks.

GB

[PMazz]

Did you select "Use FRD input model" in "Box model or input select"?

Pete

[Greybeard191]

"Box model or input select" with "Use internal box model" highlighted

GB

[PMazz]

If you want to use your measured data, you'll need to select "Use FRD input model".

Pete