Grimm Audio LS1s Subwoofer (Pair) A pair of LS1s stereo subwoofers integrate seamlessly with the LS1 or LS1a. Its phase corrected crossover at 70 Hz is already build in the LS1, so just adding the subs turns the system into a unique phase coherent three-way system. Although the LS1 on its own can play down to 40 Hz with quite impressive power, the bottom octave down to 20 Hz is hard to produce with a two-way loudspeaker system. Especially classical music does benefit from a balanced reproduction of these ultra low frequencies. Also, professionals who need to check their mix at raised SPL will value the lower LS1 system distortion offered by the LS1s option.