A gold-and-indium dual-activation-foil-based Bonner sphere system (BSS) for neutron spectral measurements was investigated. A customized polyethylene holder was designed to simultaneously accommodate one indium foil and one gold foil placed orthogonally to each other. The holder, which fits into the center of a Bonner sphere, resembles a standard 6LiI(Eu) detector. The response of the dual-activation-foil-based system was calculated using the MCNPX code with different activation cross-section libraries (ACTL and ENDF/VI for gold foils and ACTL and 532DOS2 for indium foils). To verify and correct the calculated response functions, measurements were performed using 252Cf and AmBe neutron sources of known strengths. Working response functions were determined for neutrons with energies ranging from thermal to 20 MeV by applying correction factors from measurements in well-characterized beams to the Monte Carlo-calculated response functions. Measured data were successfully unfolded with the corrected response functions and found to be in good agreement with the known spectra.