Originally Posted by phizzle

Does your JVC unit have an equaliser or some other setting like high or low pass filters turned on? You might have the filter set at something like 250Hz which would mean the rear woofers are doing SFA. Worth checking.

Also just to be sure the voice coils aren't shagged press GENTLY on the woofer cone while playing music. If it comes to life then you need new speakers.

HTH