Try using a Graphic Equalizer (a 7 or 10 band one) to boost the energy of some of the audio bands (freeware).
Wiki: "Equalization is used to compensate for the discrepancies of a room's acoustics. Ideally, a sound system would produce a flat frequency response. The frequency response of a room is examined with a Spectrum analyzer and usually a graphic equalizer, with matching frequency bands, is used to compensate for the room acoustics. This is standard practice for sound recording studios, live sound reinforcement systems and some High fidelity sound systems.
One of the most direct uses of equalization is at a live event, where microphones and speakers operate simultaneously. An equalizer is used to ensure that there are no frequency bands where there is a round trip gain of greater than 1, as these are heard as audible feedback. Those frequencies are cut at the equalizer to prevent this."