Complex sentence: Typical subwoofer products are inefficient at producing desired sound pressure levels at frequencies below 20 Hz, but the TRW is designed to cover the zero to 20 Hz portion of the sound spectrum.
Split into simpler sentences: Typical subwoofer products are inefficient at producing desired sound pressure levels at frequencies below 20 Hz. The TRW is designed to cover the zero to 20 Hz portion of the sound spectrum.