What is this wall mounted speaker?  

Looks like a custom made...
Looks like a custom made installation probably inspired by the Eames 3way speaker systems they designed for Stephen Trusonic with an exposed horn.
The horn in this case looks like an Altec Lansing, not sure about the woofer. (kinda looks like the old white woofers fisher made in the 70s and 80s.)
While it looks cool, it probably sounds terrible.

Too small of an enclosure to...
Too small of an enclosure to sound good? From the picture I don't even see how that size speaker could fit in an enclosure as shallow as that one appears to be.

Nice room!
.

I think, its a piece of wall...
I think, its a piece of wall art. I don't think its an actually speaker. First the wall is wayyy to thin, second I see no mounting hardware to hold the woofer to the baffle. JBL made plenty of woofers that look like that, just look at the L100's for example. The horn is going to be an unknown, its to small for altec or trusonic. I have seen some early ev stuff as well as western electric that was that size. But for me I have to say its not real. when these era of speakers were custom installed into homes, the speakers were usually covered with a grill usually in a cloth material...because people didn't want their guest to see the audio/entertainment system.

Any chance that
this piece might actually be mounted over a cavity in the wall, in order to maintain its shallow appearance and still accommodate the speakers ?
I can't really imagine that segmented horn being presented as an aesthetic piece de resistance . . . can you ?

Eames and Saarinen
This is a shot of Eames and Eero Saarinen's Entenza House, Case Study No 9. It's built in to a floating wall and likely protrudes into what looks like a built-in cabinet where there might be stereo equipment.
Photos of different former layouts are also definitely worth a look. Check it out on the linked Flickr search result.
http://www.flickr.com/search/?q=case+study+house+9

Could be a JBL Woofer and Horn
Very very rare if so!

Trusonic. The horn is...
Trusonic. The horn is definitely trusonic, seeing as Eames designed a lot of cabinet enclosures for trusoic. I would assume these were left over from a project and mounted in the house. Its mono era audio. The woofer does not match the horn, JBL started making white cone woofers in the 60's/70's. In that era of house and horn, no white woofer existed on the market that I am aware of. It looks like, with the larger photo, that it is painted white and the surround black. Just can't make it out, but I believe it is a painted cone.
Heres a great site, with a lot of neat era correct catalogs/flyers.
http://www.hifilit.com/

Nice site
That's a great site! Thanks.

Looks that way
to me, Cool. Thanks, analogdialog, you made my day. I missed that this was the Entenza house -- those carpeted steps with the radiused corner should have been a clue. Looks like in the colored photo the "hi fi" cabinet door, in orange paint (original ?) is open . . .
My dad-the-mechanical-engineer built his own sound system in the 'forties and 'fifties. One speaker, of course, built into a LR bookcase wall. When stereo came along, however, he dismissed it as a fad . . .
Heard lots of good music on that system, when I was young.

Mono system
I think I'm going to build an in-wall mono speaker inspired by this. I have a tube Harman-Kardon amp that's just sitting around waiting to be used, and in one room we've been planning to build a false wall.
I also like the simple cloth covered circle that you see in Nelson's designs.