A pioneer sub was connected in exactly the same way as the
amplifier, except there are no speakers to connect it to.
The second switched
live from the head unit and a second permanent live were installed to the sub.
Speaker inputs were carried from the original speaker wires on the amp
to the SP inputs on the sub. The sub was then tuned with about 40% gain and the
frequency response at about 15hz.
The result is staggering. I love hearing bass. Not that mindless (IMO)
thud-thud-thud that kids seem to like nowadays, but the clever and musical way
of using bass notes to counterpoint and complement a harmony. Now, as well as a
powerful and accurate sound from the rear to balance with the very good speakers
at the front, I can hear every slurred bass note as the player picks his way up
and down the complementary scale.