There exists a more accurate way to look at this titled question here and honestly, that will make it even clearer to address. How to create deep bass in a small box? That is something that experts get a lot of questions on because it is just highly desired these days and that is fully understandable; it would be nice if there is nothing to look at and it is just there; it is just bass and lots of it.
So how you achieve it in a small box is by having a relatively small cone. You need to have a membrane that is moving the air and a long throw; you need something that can move.
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The only thing that is what can you say that the trade-off here, then the compromise is that your efficiency is significantly lower that is why you see these enormous amounts of watts for many of these really long thrown cost airy woofers like two thousand three thousand watts.
One could even wonder once looking into it it is like you know these stage equipment woofers why aren’t we using those instead you know for this purpose? Because they have like 99 maybe 100 decibels of high sensitivity; it is very efficient from just a little bit of power, it can play really loud.
Even if you have like a large subwoofer like 18 inches 21 inches and a huge PA sup or it might only play down to 36 Hertz whereas you can have a little box for your home theater playing down to 20. It would just play way less loud, you know, but it will play really really deep so that is your trade-off. It is hard to get both; even in a small box for the large row, you need burn-off thousands of watts if you need that to be loud for like what you call a club or something like that.
So I hope you get something out of that then you know what you are up against like if you want really deep bass is gonna cost you some energy particularly if you want the box to be small then that is causing even more energy to get down there so that is the cruel reality of physics I hope you got something out of it. I know it is a bit it has a little bit of a negative taste to it but it is real it is you are up against.
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Anyway, that is all I wanted to say on the subject just briefly; I know there are a lot more calculations to it. But I believe to answer what 12 inch subwoofer has the deepest bass or how can you get the deepest bass out of a small subwoofer, this much info will be enough.