Before DSPs (Digital Signal Processors) became commonplace, analog crossovers like the Pioneer QXE1047 were the secret weapons of serious car audio competitors. This device allowed users to split audio frequencies and send them to the right speakers—bass to subwoofers, mids to door speakers, and highs to tweeters.
Ironically, some sellers list the original paper manual for sale. Search for "Pioneer QXE1047 owner's manual original." Expect to pay $10–$20. Once you buy it, scan it and upload it to a free forum to help the next person. pioneer qxe1047 manual