Butterworth band-pass filter transfer function
okay, the magnitude frequency response for a general $N$th-order Butterworth lowpass filter is:

$$ \Big|H_\mathrm{LP}(f)\Big|^2 = \frac{1}{1 + \left(\frac{f^2}{W^2} \right)^N} $$

for bandpass filtering, centered at frequency $f_0$, this substitution is made to the LPF:

$$ f \leftarrow \frac{f}{f_0} - \frac{f_0}{f} $$

so then it comes out as:

$$ \Big|H_\mathrm{BP}(f)\Big|^2 = \frac{1}{1 + \left(\frac{\left(\frac{f}{f_0} - \frac{f_0}{f}\right)^2}{W^2} \right)^N} $$

blast that out and you'll have the frequency response for an $2N$th-order Butterworth bandpass filter.