Sorry but I have to say you lost most of the bass-reflex effect so most of the frequencies below 100-150 hz were lost with such modification. You still can save something trying to make some hole ( about 1/2 inch) in some place but should look for the best to get the resonance frequency of the speaker.
The size of a loudspeaker with his woofer is not taken at random, but perfectly calculated, more coming from Tamiya, in fact that's the reason they sound so good. If you had made the test whitout the plastic case would be realized the amount of loudness you lost.