Best speaker for medium to low power tube amps??

The new Audio Physic Virgo would be a nice choice. In a room your size they would like 50w or more I'd imagine. Check out the Immedia site for set-up instructions.

2nd of the Virgo's. Either version. The new ones are better, the old ones are a steal used! BAT VK60 makes a nice match.

I got mine from someone who had been driving them with a 50 wpc tube amp in a room about 12 x 15. He had been very happy with that combination. ( Sold because of low WAF for multiple systems. ) Other sources have also been happy with the Shearwaters ( 88-89 dB/W sensitivity ) combined with tube amps in that power range.

I myself am using a ss Celeste W-4070se ( about 70 wpc ) with my Shearwaters There is gobs of power for my 15 by 22 room.

Another possibility might be Reference 3a. The DeCapos are rated at 92 dB/W. I heard them do very well with Antique Sound Lab 10w tube monoblocs at the 2001 Montreal show.

You might want to consider Revel Performa F30s; I am running them in a 12.5x19.5x8 room with a Jolida SJ502a which puts out ~60Watts/ch (I am using Ei KT90 power tubes; I'm not sure if that increases the power at all, but the amp is rated to deliver 60/ch).

I wanted a speaker that did deep bass as well as a really nice midrange and good detail/air etc. Having auditioned several in the 3-5k price range I settled on the Revels and am very happy I did. I was a little concerned that the amp would not be able to drive them well, but it has no trouble at all (I rarely take the volume past 25%; beyond this the SPLs become quite uncomfortable, though not at all distorted- I just can't listen that loud for any length of time :).

As always, audition before you buy :).

i like the jm lab electa series. the older ones are cheap now and sound awsome. the sonus you mentioned are great speakers as well.