Evaluating loudspeakers
Not an easy job. A loudspeaker produces a complicated 3 dimensional sound field, which heavily interacts with the environment. Even at a distance of a about 3 feet the reflected energy is significantly bigger than the direct energy at most frequencies. Typical loudspeaker measurements are


On axis response in an anechoic chamber
Full 3D response in an anechoic chamber
Radiated power in the far field in a highly reflective environment.
Room responses taken in "real world" setups, deriving a perceptually relevant spectral metric and averaging over a large number of environments and placements


Each of these measurements require specific measurement methods and techniques which are also not trivial. 

Anything you can do with a single microphone in real room will most likely be either useless and misleading. The box is also not a good idea since any box has very strong internal acoustic modes and what you will be measuring will be dominated by these modes regardless of what the loudspeaker is doing. 

Depending on the physical size of the loudspeaker and the size of your measurement space, you may be able to pull off a near field measurement with careful time gating of the impulse response (loosing a lot of low frequency resolution in the process). Getting this right is a lot of work and in my opinion not worth the bother.