klipshorn speakers

He should just be sure to have two corners that will allow the listening chair to be centered and far enough back.

Yes, these at high volumes might do structural damage to his home.

They don't do super deep bass, but they will play very loud without effort. I added a pair of 15" direct radiator subwoofers to a pair of K-horns years ago. my die-hard horn-loaded-only friend was impressed with the extension. I think I crossed the subs somewhere around 40 Hz and they would play down close to 20 Hz. Those subs could seriously shake the house with a couple hundred watts each. The K-horn didn't need nearly as much power to keep up with them. If I was willing to shatter my eardrums I'm sure the K-horns could have left the subs in the dust.

Excellent speakers - but you may wish to Google their dimensions before giving your blessing.  :o)

+1 asctim
They get crazy loud, but bass shaking not so much. I ran mine with a Velodyne 15" sub and that did the trick. 

I'm running corner horns with 2 watts and  Soft Serve by Soul Coughing will punch you in chest and vibrate furniture.
You realize premature deafness is a possibility with the sound pressure levels these can produce with very little wattage?