Building a simple high pass filter

[mjg100]

I am not sure if this is the right place to ask this. If it is not the right place please let me know where to post. I have built some mid bass modules that I want to use for the 40 to 150hz range. I would like to build a high pass filter at 40hz. From what I have read I need to install a capacitor in series on the + wire before the amplifier and install a 33k resistor in parallel right after the capacitor. The equation to figure the capacitor is; C=1/(2)(pi)(R)(F). Where:
C=capacitor size
pi=3.14159
R=33k
F=high pass wanted

For 40hz high pass I get C=0.048uF. Is this correct? Am I also correct on the installation procedure? If not could some one explain how I calculate the correct value and install it.

[aznboi3644]

What ohm load?

http://www.the12volt.com/caraudio/crosscalc.asp

[mjg100]

Originally posted by aznboi3644
What ohm load?

http://www.the12volt.com/caraudio/crosscalc.asp

Home theater application using 4 ohm driver. I looked at your link and I thought that when a capacitor is placed in series after the amplifier the high pass is not very consistent. In other words the crossover point varies as the speaker impedance changes?