sorry for late reply.
got some time. thought link vids here.
some FAQs about sub wiring. Speaker / Amplifier Wiring FAQ - Tutorial
1. series connection - 8 ohm
More resistance , less power taken from amp by sub
done mostly by car dealers as easiest method.
Your sub is in this connection currently , i guess.
(Note- this is the only method you can use for your sub WITH 4 CH AMP , however with monoamp you can use 2nd method of parallel connection)
2. Parallel connection - 2 ohm
less resistance , more power (almost maximum possible) taken by sub from amp.
Use this method only if you are planning for monoamp.
And use this calculator to tune your subwoofer box.
in the vid your port looks very huge.
so i suggest you to check at what frequncy it is tuned. because in ported box tuning of box matters a lot.
enter - dimension of box and dimension of port in this calculator , add woofer displacement around 0.4 cu ft. you will automatically get at what frequncy your subbox is tuned.
try to set it at 30 hz by changing the port dimensions (because it is the only option that can be changed now ) , and if modification in port needed , close the remaining part of port by MDF or wood.idk what it is called
even i made mistske by making huge port and tuned box at 70 hz previously. but now closed most of it now and getting proper bass punch.
and note , port must have 4 walls (not 3) , so do modification according to it.
for dimension of your box , dont add the upper part of the box , that is , below that glass and above the subwoofer , if it is not connected by anyways to that of actual box that is below subwoofer cone..