Cascade the biquads together to create an equivalent IIR filter.
        let cascade = cascadeBiquads(coef, coef);

        // Since we're cascading two identical biquads, the root of denominator
        // of the IIR filter is repeated, so the root of the denominator with
        // the largest magnitude occurs twice.  The impulse response of the IIR
        // filter will be roughly c*(r*r)^n at time n, where r is the root of
        // largest magnitude.  This approximation gets better as n increases.
  