I have 4 Dayton Pucks attached to the underside of my organ bench.
http://www.daytonaudio.com/index.php/tt ... haker.html
The reason for using 4 units is impedance. Each unit is of 16 ohms. They are wired first into pairs in parallel, creating impedance of 8 ohms to each pair. The pairs are then wired together in parallel to create 4 ohms mono as required by the subwoofer amplifier I used. The wiring diagram to show how this is done is included in the user guide, which is downloadable from the Dayton website. I live in Sydney, and the pucks are not available from any dealers in Australia, so I imported mine direct from the US.
The subwoofer amplifier I used was one of these, which I purchased from a local electronics store.
https://www.altronics.com.au/p/a2451-op ... amplifier/
With careful adjustment of the subwoofer amplifier's controls for volume and active crossover I've tuned it to start responding half-way down the 16-foot octave and into the 32-foot octave. I listen only through headphones, and the experience of realism generated by the pucks is nothing short of astounding.
Highly recommended!
Andrew