You do, indeed, need to put the speaker in a box. It may sound good like that, but it will sound so much better in a box, and it'll damage itself if you use it much in the open like that. (How do I know..? Don't ask..! I, too, was young, foolish, unexperienced and broke, once...). Once you get a box, the important part is to make sure that there's a good, airtight seal between the rim of the speaker and the box, and the the speaker is securely bolted to the box.
You can try an experiment, whilst waiting. Find a stout cardboard box, of any reasonable size (roughly a 30 cm cube or so; it's not critical...). Cut a hole in one face, perfectly round, and just the size for the speaker to nestle into, supported by its rim. Feed the cable through the back of the box, and listen to the difference when the speaker is firmly in the hole, and when it's lifted out. It should be quite conclusive. Worth a try..?