Subwoofer w/ most SPL's For Music Only System

how much detail is in deep bass a bass horn will let you hear this

In terms of power, the horn design is very efficient but you will lose some details from transients and the same can be said for ported designs or passive radiators that boost LF power through resonance. For low cost and high SPL output design you cannot beat a horn.

A subwoofer loses detail due to massive driver excursion

Large excursions in a sealed box are indeed a problem for low cost drivers (small magnets, long voice coils) with correspondingly low levels of linearity (Xmax). The bass output will quickly compress and harmonic distortion will increase dramatically at higher excursions. (although this design may work very well at low SPL levels, more accurate than a resonant design)

Bass horns are exceedingly costly (check out the 'Living Voice' horn sub of old), they are also usually the size of a baby elephant, and don't go down nearly as far enough, 30hz if you are lucky (or unlucky), a friend uses 2 of the smallest REL's (Q50's I beleive) for his med/large(ish)hornloaded speakers to great effect as he only wants to underpin the bass he is already getting anyway (music only system). There are some seriously good musical subs out there for not much wonga. 2 subs are apparently better than one. I personally would love 2 SVS PB12/Ultra/2's!!
That should alter the foundations a tad!!lol

I would look at the Rel subs. I looked at a lot of subs and the Rel out did them all.

re: 21st Century BASS HORN ( http://www.lyngdorf.com/index.php?option=com_content&task=view&id=27&Itemid=55 )

Then there's this:

http://www.genelec.com/products/subwoofers/7073a/