Actually, it is not a problem of the radio. Radio stations do not provide the wide range spectrum of sound as the CD. They also do not broadcast the frequency of the lower mhz notes at a high enough amount for it to be sent to the sub. You do get the signals, just not boosted enough for a high register on the sub. Not enough watts to produce enough sound in the sub that is.
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Eric
Now proud owner of a '05 Mazda 3 HB!!