Alright well i dont know wether to go with sealed or ported to fit 2 Alpine 12" Type X subs. The main reason i carnt decide is because i have never hurd a sealed box in the flesh. My question is will a sealed box still give me that thump? and keep in mind i am not aiming to blow out my windscreen with ridiculous bass. BUT i still want it to have a good decent thump that will have an impact.
a sealed box is about -3dB down from ported. -3dB is equivalent to half the power, or going from two subs to one. Half the audible volume would be -6 to -10dB for reference (decibels aren't linear. it's a log scale)
Yes a sealed box still thumps. It will be a faster responding box, it will play more deeply, will not require a subsonic filter, and it will be a smaller enclosure. The type X sub is a high output, high excursion SQ sub. It's designed to be accurate and fast, and to stay very linear even at high excursion. It's not an SPL sub. It will perform outstandingly in a sealed box with adequate power. I'd recommend you double the sub-side face of the box (1.5" instead of 3/4" MDF (double sheet)) to support the driver weight and reduce flex in teh box. You might also consider the use of bracing internally, and polyfill (loosely, 1/3 the box volume)
You should get great results.
If you really want a nice box, use white ash instead of MDF.