The 7100 Plus includes a single subwoofer in a fairly unassuming enclosure, measuring about 22cm x 34cm x 35cm. The subwoofer enclosure is crafted of fairly high-density fiberboard, and is quite sturdy. The unit is finished in the same metallic color as the satellites, and features the same non-removable cloth grille.
Fig 2. The subwoofer, featuring a 6.5" woofer and two bass-reflex ports in forward firing direction.
The subwoofer features a single 6.5” long-throw woofer, oriented in a forward-firing direction. Two ports, located below the driver, open up the enclosure. The woofer is driven by 50W RMS of power, which, combined with 10W from each of the five satellites, brings the total system power up to 100W RMS.
Fig 3. A look inside the subwoofer, notice the wooden enclosure, the 6.5" woofer and the two bass-reflex ports
The subwoofer picks up at the crossover frequency where the satellites leave off, producing sounds at 250Hz and below. A crossover is essentially a network of capacitors and inductors that divide the signal into different groupings according to frequency. One set of tones is then passed to one speaker, while the other is passed to another. In the case of the 7100 Plus, the crossover is set at 250Hz, meaning sounds above 250Hz are handed to the satellites, while the subwoofer handles sounds below 250Hz. 250Hz is slightly on the high side for a crossover frequency.
The problem here is that sounds above 100-200Hz still retain a significant amount of directionality. As a result, listeners will clearly hear the subwoofer, and be able to pinpoint its location. Ideally, a subwoofer should be heard (or rather felt), but its location should not be detectable. Unfortunately, the 2.5” satellite drivers can’t handle sounds below 250Hz too well, so they need to be passed off to the subwoofer, in this case.
The S/N ratio of the subwoofer's amplifier is, again, in the neighborhood of 55dB, which is quite low. This indicates that we may be subject to higher levels of background noise than usual, but we’ll reserve judgement for the listening tests.