[raymondlin]

Thanks to a member in HiFichoice forum here's the answer why speakers have the cabinet..

"Well here goes, as a speaker moves in and out the air at the back of the speaker is acting in reverse of the front. i.e. as the speaker compresses the air at the front, rarefaction of the air occurs at the back. If you listen to a bass speaker on it's own you here both of these waves, this is know as an acoustic doublet.
Now to stop this back wave canciling out the wave at the front it has to be brought into phase with the front or canciled out.
You could use a flat baffle to do this i.e. a large flat board with the speaker mounted in the centre. However due to bass frequencies being low you would need a board about 4 metres on a side. This is an open speaker (sort of!). You could fold the baffle to create an open-back cabinet and reduce the size of the baffle. (some TV's and radios use this.)

However enclousures [(closed,bass reflex, or accoustic labyrinth) have the advantage of altering the resonate frequency of the driver and moving it higher or lower up the frequency spectrum. However the ideal resonant frequency of the drivers depends on the other drivers in the loudspeaker, the crossover points and what the speaker is designed to sound like. I'm afraid after this point I can't tell you much more as I haven't designed a speaker system (Yet!)"

Thanks Mike sworld.

 

[Audio-Me]

You've got it, air compression. Sort of like bass compression in tubes isn't it?

I like good coloration anyway, paper cone in mdf, or metal drivers in metal box.