Could anyone please send me to a sub that would work better than this tuned @ 20hz?
We have been over this before with you, but you never seem to understand. You do NOT pick a tuning frequency out of thin air. Tuning frequency is dictated by the T/S parameters of the driver. And once more, the tuning frequency is not the low frequency the sub will operate to.
The best guide as to how low a frequency a sub will output is the fundamental resonant frequency of the driver, Fs. In practical terms the f3 point of the driver will be somewhat above that for a ported enclosure, and far above it for a sealed one. However a sealed enclosure can be equalized and a ported one can not. Although equalization is limited by the power handling of the driver and its excursion limit.
The driver you selected has an Fs of just over 26 Hz, so if you model it, you will find that it will probably have an f3 around 30 Hz.
It is the electromechanical specifications of the driver that determine this. If you measure the impedance of a driver in a ported box, you get a trace like the one below.
The tuning frequency is at the bottom of that saddle of impedance. You DO NOT get to determine that, the design of the driver does.
However that tuning frequency is NOT an indication as to how low the driver will play, that is actually always BELOW the tuning frequency.
So in your search for a driver to play down to 20 Hz, you need a driver with an Fs a little below 20 Hz and a Qts in the 0.35 to 0.4 range.
But you have to model it, and the low point of the saddle of the impedance curve has to be the tuning frequency. If you try and make it something else then the sub in fact will not perform well, and not go as low as it would if the tuning frequency was correct as determined by the T/S parameters of the driver.
