The OB-7 Plus is a loudspeaker kit available from GR Research.
The driver complement uses the BG Neo 3 pdr covering the range from 1,800Hz and up. From there it hands off to a pair of M-130/16's mounted in an open baffle and covering from there down to a crossover
point of 225Hz using a first order electrical slope. It then hands off to four M-130 woofers wired in a series parallel configuration. These are mounted in a sealed box and cover an area reaching down to a side loaded SW-12A 12" woofer. The SW-12A is also loaded into a sealed box at the bottom of the enclosure.
The open baffle area to the sides of the M-130/16 woofers are covered in grill cloth but can be left completely open. These speakers have 91db sensitivity with 1 watt/1 meter and have about a 6 ohm average impedance load with a minimum impedance that drops to 4 ohms in the 4 to 5kHz range. The lower frequency range from 80Hz and down stays above 8 ohms. This makes them fairly easy to drive and easy to get good output levels without tons of power.
A small sub-woofer plate amp fits easily into the back of the enclosure
and powers the 12" side loaded sub. The separately powered sub
makes the OB-7 Plus easy to integrate into any room. The output level of the bottom end can easily be adjusted to match the rest of the speaker regardless of the room size and low end room gain present from the room. This also allows the end user the flexibility to crank up the bottom end or lower its output as desired.