What are the smallest speakers that are clean and flat down to 20hz?

I would consider looking at the DIY site from Troels Gravesen. Lots of his kits show the speaker response and the room response, followed by the final outcome.  You could find it illuminating.

http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm

Best,


Erik

Headphones!

Grado made a line source array that they showed at CES one year, just for fun. It made decent bass but it had a lot of drivers in it. Seems to me it was over 6 feet tall and they won't be manufacturing it.

Otherwise you're simply going to have to have a big speaker.  My speakers go to 20Hz and have two 15" woofers. You probably can do it with one. The smaller the driver, the more excursion it needs and that's your limit. Bruce Thigpen got around that limitation with his subwoofer fan.

Click on the link below and then products (TRW-17):

http://www.eminent-tech.com/main.html

From the page:

A conventional speaker cones displacement must increase four times for each halving of frequency to maintain the same output. This is why conventional cone woofer companies are trying to develop “long throw” woofers. Although inefficient, cone woofers work fine above 40Hz. Below 40Hz however cone woofers quickly run out of travel and the output diminishes rapidly.

Barefoot Monitors are probably the smallest high performance speakers.

The MM27 has the smallest footprint and can compete with speakers many times their size.

Physics can be a pesky thing, and the mutually exclusive nature of including "small" and "clean at 20 hz" in this post does seem a little paradoxical. I use 2 RELs in my hifi rig and they're sort of smallish I suppose, as are the drivers in my Silverline Preludes (3.75" woofers)…I have a 92 lb 500 watt Mackie studio specific sub (in my studio specific studio) with 2 12s (active and passive) that supposedly does 19hz…but it's on the large side. So, no free lunch. 20hz…hmmm…large Wilsons maybe?