theres no fun in paying someone to do it
i have used a few box designs all up, the pioneer eventually blew in a generic ported box and lastly the type-s gave up in a small sealed box, near on a cubic foot which all round i felt sounded the best but seemed to plateau at very high volume.
in between the 2 above mentioned subs i used the TWS307D2 as bang for buck spec wise it looks a winner but after 3 enclosures i got rid of it cos i couldnt shake this mid-low bass emphasis it had which drowned out the sub bass. firstly i used a small sealed enclosure as per pioneers recommendations then a larger packed sealed enclosure and lastly a slot ported box i had made which is now a makeshift coffee table in the garage (internal measurements 300x350x350 + another 50x300x350 slot port) this gave me my sub bass but only at high volume and in hind sight i went a little too low on the tune for the box. there was hardly any bass response on low to moderate volume and it weighed a tonne. i've also listened to this sub in the prefabricated pioneer enclosure and didnt really like the sound, it was in a BA ute so that may have something to do with it.
i want to steer away from the 600+ price bracket for the next sub as its stepping into the next level of audio where my front stage cant keep up, which will end up snowballing and next thing i know ive got a system worth more then the car, been there before.
im no audiophile but like to know tricks of the trade...
so from what ive read the enclosure is the weak spot. i can stick with my current setup then pick a sub, get a custom box tuned for my application and go easy on the gain...im of the school of thought on letting the amps do the work as far as tuning goes and try to make minimal changes at the head unit only to adjust sound quality between different bitrates