check the recommended volume for the speaker box as this can effect its sound quality/loudness greatly.

make it as light as possible

face the sub backwards and you will get better bass.

I have tried:

8" bazooka tube mounted directly behind back seat on drivers side with pot pointing to passenger side and this was the most efficient location for this set-up. turning it other directions lost bass.

10" alpine in a ported box (port is vertical) and found the most efficient location was speaker facing bootlid.

2x 10" no brands in a sealed box, most efficient facing backwards (towards bootlid)

I custom made a box a few years back top house the 2 10" and face them towards the back seat. sounded ok, but seats needed to be folded down for maximum bass otherwise it was quite muffled. The box was really heavy and lowered the rear of the car about an inch.

have also tried the 2x10" no names with the alpine in the same box and it was so poor that it lasted less than an hour before I took it out.

all of the above are powered by an old school apline deck 25wx4 and an alpine mrf/v amp rated at 300w max.It's a tiny amp but has never let me down.

Hope the info is useful.

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