I heard the Box

I never quite followed what people meant when they commented "All I heard was the box"
when listening to a speaker. 

I experienced it now twice in the past month. Once with some Dynaco A25s and then with a pair
of Electrovoice EV 4s.

My problem is now that hear the box, I can't seem to unheard it. 

These old gems were meant to be used in my office mostly for FM radio background.

So my question is- A load of both of these speakers were sold over many years so
how did people get around this issue?

I am now leaning toward an Andrew Jones dual concentric bookshelf solution.
Those I have heard in my home and sounded quite acceptable at $600 new.