I was so impressed by the Nelson-Reed 8-04/B
loudspeaker's low-end range that I seriously doubted the add-on subwoofers could add enough of significance to be cost-effective.
I was wrong.
Two of the subwoofers were provided, along with the necessary electronic crossover unit. Each 1204 unit contains four 12" woofers in a very solid sealed enclosure, with two facing to the front and two facing the rear. The electronic crossover has three controls, besides the AC power switch: a hardwire (footnote 1) bypass switch, a stereo/mono switch, and a subwoofer level control. In the stereo mode, the low frequencies are kept separate, left from right; in mono mode, they are blended together for feeding to a single subwoofer. I will not resurrect the question of whether or not it is important to maintain stereo separation into the LF range, except to echo N-R's observation that there is no LF separation on analog discs to begin with; the lows are mixed together, to limit vertical excursions of the cutting stylus that could cause it to rise above the disc surface or, worse, dig into the aluminum base of the master disc.