Only getting very muffled sound,have changed diaphram,but prob still exists,can you help please

Getting very muffled sound usually could be attributed to either the cables supplying the speakers being bad or torn speakers. The cable problems usually should be traced as far at where they get connected to the unit as a breakage in any of them could cause such problems in the speakers.
Secondly the main speakers in the speakers could be torn therefore the bad sound being produced try to get all the component speakers checked to ensure that they are all okay. if after checking these the speakers are found to be good then try an alternative sound souurce to ensure that the problem is not from the sound source instead of the speakers.
Hope this solution has been helpful?