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Message: <blockquote data-quote="T3mpest" data-source="post: 8247616" data-attributes="member: 560148">Are we talking in a sealed box and holding frequency response constant, then yes those scenarios will give you equal ouput, but things get funky as AKADJ pointed out down below.  However, here are the basic points to understand1.As you go down an octave (halfing frequency) to keep SPL equal you need to move 4x as far.. So if a speaker puts out 100db by moving 10mm at 40hz, to put out 100db at 20hz, it would need to move 40mm..  As you go upward the opposite happens, so higher frequencies need less xmax than lower ones.  Generally speaking most speakers are NOT xmax limited above 40hz, even 10-15mm of xmax can be painfully loud (literally) at those frequencies and often the power levels needed to get a speaker to even those levels is enormous.. Ports have a similar effects as I'll outline below.  However for reference, I have a very powerful 21 in my car right now with 15mm of xmax and without at least 2k on tap, you'll never reach xmax at any frequency above 30hz.. If you port it and your talking 40hz and higher, you'll likely never see xmax until 4k or so of input.2.Motor force helps determine how much cone movement you get from a given amount of input power.  This is why subs with low xmax can still be loud, especially ported.  When a speaker is ported, the woofer and port are out of phase and the port fights the cone, damping it's movement.  This reduces cone excursion, however, since that's where the port is most sensative, you get a lot of output from the port with very little movment from the cone..  That's why 30mm xmax weak motored subs still may not get as loud on a meter as a 15mm xmax high motor force sub.  The trade off is that a sub with a high amount of motor force relative to it's weight has a high resonant frequency, or fs.. This makes it less effecient at playing low notes in the first place, which is why they excel in ported boxes.  Sealed the roll off very fast.3.Power compression and BL compression effect the actual power levels needed to reach these cone excursion levels..  To get that single 12 to 30mm of xmax might require on paper, 900 watts.  However as the coil heats up it's impedence rises, reducing the power your amp can supply.  In addition as the coil leaves the gap, the motor force of the speaker drops.  As I mentioned in point 1, that means your speaker now needs MORE power to continue to move further.  So now   Instead of 900 watts a modelling program would tell you is needed, it actaully needs 1600 watts AND your 2000 watt amp has heated the coil up so much your amp can only put out 1500 before clipping //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif  So often times, more cones moving less distance is more effecient overall because both those effects are minimized.</blockquote>

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