what is a big speaker?

That is a stupid tittle, but what I am confused about is for example, I have large VMPS speakers wich employ 2 10 inch woofers and a 10 inch passive,with a 3inch by 48 in ribbon mid and 3 small tweeters, now the box is a pretty large coffin, but are 2 10 in woofers and the ribbon mid with the tweeters a truely large speaker when you break it all down?
And other then physical size, what makes a speaker too large for any room....if you dont listen at concert levels?
If we drop the "looks" part and only go with sound quality...it's not a matter of "to big", wrong speaker for the room would fit better here.

Very large speakers can demand setup well out into the room, many are multidriver systems which require greater listening distance for the drivers to integrate properly.

Some large speakers work well in smaller rooms...the old Snell Type A's I loved so much years ago come to mind.

I have a pair of VMPS ST/R's (15'/12' actives...15' passive), that did a great job when I had them setup in my small living room 12'X 18'.

On the other had, my Apogee Duetta Signatures did not sound good in this room...to many restrictions on placement.

So, while the VMPS will do 17hz and the Apogees only 28hz...the VMPS work best in smaller rooms because of less placement issues.

All my speakers sound best in my big room...even my small VMPS bookshelf.

It is almost impossible to generalise in this way.

...other than physical size, what makes a speaker too large for any room..?

LF bass response, accuracy, SPL level and dynamic range should all be better with a big speaker (if driver quality is maintained).

However, a big speaker with several lower quality drivers can sound worse than a small speaker with a higher quality driver.

Since most speakers sound quite different at high versus low SPL levels; there is often an optimum level for a particular speaker. Typically, a small speaker may strain at high levels, which sounds dull and compressed in the bass and harsh in the mid range. Conversely, a large speaker may sound dull or lack clarity in the mid range at low levels.
A BIG speaker is usually generalised when your wife first looks at them for the first time and says, those are big speakers. Either they go or I do!
make sure you get the ok from the boss before you hand over any cash!