Loudspeakers with a wide sweet spot

Although I am a big fan of horns and field coils, the speaker with the widest sweet spot that I have seen/heard so far is made by High Emotion Audio. The tweeter is unique and patented. It goes down to 2KHz- well within the range of image definition. It radiates nearly as well to the sides as it does forward. You can easily hear the soundstage image while standing off to one side, not even between the speaker. They are also not critical of setup- the image just grabs hold even if very casually placed.

This is one of the more high-speed, detailed speakers made, while being relaxed- an uncommon combination. The speaker (S7) is easy to drive with tubes or transistors. The retail is about $5,000/pair.

The tweeter is unique and patented. It goes down to 2KHz- well within the range of image definition.

This reminds me of the Energy Pro 22 - they had a hyperdome tweeter that they made themselves and which was crossed over at 1.8 Khz. Great speakers with a lovely natural wide dispersion and very reasonably priced back in their heyday. No doubt Dr. Floyd Toole had some influence on them. Of course, crossing over a tweeter that low has its problems in terms of maximum SPL without distortion and compression and potential to "blow up" but for a bookshelf the Pro 22's were outstanding sound for their modest price.

Full disclosure...I am a dealer, but try to be honest anyway :-)

Second the Verity. The new Finn is well under $10k and has a wide sweet spot. The Finn is one of the new, higher-efficiency Verity speakers that are much more tube freindly.

I have found that Shahinians are very good in having a wide social image which can be heard from many positions in the listening room. I spent a lot of time listening before I sprung for mine.

The speakers I own (Sforzando JL-1s), and other speakers designed by Fr. Richard Davidson (the old ITC speakers from way back, for example), would meet your requirements. You'd need me to get you in touch with him, though, as these speakers are not really commercially available or something you could listen to other than at a few people's homes. Generally I agree with the suggestions about omnis, and I have heard Avalons off-axis sound quite good, though I must say that they really can lock-in when you're in the right spot. One other more or less conventional speaker that I have heard and believe was not mentioned above that seems to do well from off axis is the von Schweikert VR4; I'd imagine that the entire VR line probably would be similar.