I am running 1 12 inch w7 i was wondering if a little bit smaller or a little bit larger box (sealed) would create more or less spl i built a box to the spec's but i think it came out a little smaller and i was basicly curious on the matter
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89 honda crx 1 15" Power HX2 jblbp1200.1 rockford coaxials 4 channel comin soon
A larger box would probly give u what u want. Typically a larger box will kick out lower bass than the smaller box....not sure on technicalities but thats pretty much what i've come across.
Larger box = lower bass response, yes. More SPL, no, not that you would notice given what you said. But you would probably have better SQ with the larger size given by the manufacturer.
With very LARGE differences in volume, say comparing 1.25 to 5 cu ft., the larger size will be more efficient and will make a noticeable difference in how the power is applied. Or also in the case of small sealed vs. larger ported., the smaller sealed would need more power to achieve loudness and so can seem to be inefficient (not loud enough) if there isn't enough power available to give it what it wants.
Best thing for you to do is to pull out the woofer and fill the box with polyfil to create the impression of a larger volume. You can cheat up 10-30% this way.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.