What makes speaker's sound big?

Mark & Daniels. I have the 1st gen Maximus-Ruby. They use their own version of the AMT driver and a 5" woofer (crossover at 900Hz). Terribly inefficient but with a proper amp they have amazing dynamics and soundstage. The 2nd gen is supposedly even more refined. 

radiating area of drivers
dispersion characteristics of drivers
distance between drivers
baffle design
boundary reflections
placement

When talking about sounding big that usually translates to full extended bass. Powered subs are your friends there. Big = powerful and the bass is where most of the power in music occurs. It takes exponentially more power to deliver flat response as the frequency decreases and that power must be converted to long wavelength sound waves so that pretty much explains it. Tiny drivers/speakers alone are more challenged to deliver full extended bass and all fall short alone to some extent.

This is a great subject and one I have thought about, or wrestled with for some time. Thanks for all the very good views and thoughts expressed.

I owned Martin Logan SL3s as primary audio speakers for 16 years and loved the immersion. I equally agree with getting that from Maggies! And I think it is the bi-pole nature that does help in that aspect.   I moved finally to Dynaudio Sapphires and they were a much larger sound than any of my conventional coned dynamic speakers. Yes, "horsepower" (good one!)

But the brand I'm living with now are Raidhos and although the D2s won't do what the much larger ones will do I still love the tonality and rich clarity plus tight bass to near 30. But, to enlarge that sound I have dialed in an REL Britannia B1 at 28Hz and low volume and it opens up large halls.

There are lots of great inexpensive powered subs that will integrate better than most of years ago, and they uncannily open up everything for a subjectively larger sound.   It's almost stunning that a simple $1k SVS SB-3000 is pretty much the equal of the B1 (or better?) at 1/3 the price. Unreal. Maybe that is one of the least expensive ways of getting 'bigger sound'.  Fun topic.

'Di-polar' on the Martin Logans and Magneplaners. Oops, more coffee.