Subsonic filter options

[Jimmy154]

Got confused again 😀

Is the crossover down 3 db or 6 at f? Using these equations: Passive Line-Level Crossover

 

[Jimmy154]

Looks like R2 (with the vertical line above it) has to be positive for the circuit to function properly, but it is recommended that I use 5K-10K resistor for the 12 db/octave slope. All values above 1K ohm for R1 will cause R2 (with the vertical line above it) to be negative, since my amp input impedance is 10K ohm. What do I do? Here is the link to the formulas: Passive Line-Level Crossover

Looks like my only option is to choose a R1 resistor lower than 1K ohm, correct?

 

[Jimmy154]

Can I use the amp input impedance as the R2 resistance without using a resistor?

Values would be:

R1=1k ohm
R2 or amp's input impedance=10k ohm
C1=1.06e-5 F
C2=1.06e-6 F

or should I use?:

R1=500 ohm
R2=5k ohm
C1=2.12e-5 F
C2=2.12e-6 F
R2(with line over the 2)=10k ohm

Or should I use other values? It's a 12 db/octave high pass filter at 15 Hz.

 

[Jimmy154]

I can see I have ostracized myself from the diyaudio community, possibly due to my signature.

I'm gonna have to go it alone. Wish me luck friends (and enemies).

 

[Artie]

Which BA amp do you, (or your friend), have? Don't the Bostons already have a built-in x-over / filter?

 

[Jimmy154]

I have the GT-28. It does not have a subsonic filter. Although I do believe it might come with some sort of optional subwoofer control module that I do not have.

I'm going with these values:

R1=1k ohm
R2 or amp's input impedance only=10k ohm
C1=11.6 uF
C2=1.1 uF

Hopefully, as I understand it, this will give me -6 db at 14.5 Hz.

 

[Artie]

Those numbers look good, except that you'll have -12db at your "f" value. But thats good in my book. Try it and see.

 

[Jimmy154]

Hmm . . . I was hoping for -6 db at 14.5 because my friend's subwoofers are tuned to 18 Hz roughly. Is it a problem that I used only the amp's input impedance as the R2 resistance or impedance?

I thought 12 db/octave Linkwitz-Riley were down 6 db at "f":

http://www.bcae1.com/images/gifs/xo2ndlra.gif

 

[Artie]

Is it a problem that I used only the amp's input impedance as the R2 resistance or impedance?

I'm not sure. Someone more knowledgeable than me will have to field that one. It sounds feasible though.

I thought 12 db/octave Linkwitz-Riley were down 6 db at "f":

I was just going by the fact that its called a 12db/octave curve. It may well start at -6db.