My receiver has a "Subwoofer pre-out" out. My subwoofer has three possible inputs under "Line Level In." 1. is LFE and the speaker manual says if receiver has LFE or subwoofer out to connect here. 2. and 3. are L and R as in RCA cables. With the cable supplied by the speaker manufacturer, I can't get anything out of the subwoofer using the receiver's Subwoofer pre-out output. If I connect straight from the DVD player to the sub it works fine, but not through the receiver. Why not? Am I doing something wrong? Using a THX optimizer on "The Incredibles" DVD all of my other surround sound speakers work as they should, just not the sub (unless I've hooked it up straight from the DVD player).
Thanks for any help
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Depending on the model, there are two ways to connect a subwoofer to an amplifier, receiver or processor. The best way is to connect the subwoofer to the SUB OUT or LFE output of a receiver, but some subwoofers can be connected to the speaker level outputs of the receiver or amplifier.
1. How to Connect a Subwoofer to the Subwoofer Output
The preferred method of connecting a subwoofer is through the LFE or Subwoofer output (SUB OUT) of a receiver. Almost all home theater receivers (or processors) and some stereo receivers have a subwoofer output. The LFE (Low Frequency Effects) is a special output for subwoofers and is often labeled 'SUBWOOFER' not LFE. 5.1 channel programs on DVD discs have a dedicated .1 channel output with bass-only content that is best reproduced by a subwoofer. Connect the output of the LFE or Subwoofer jack to the Line In jacks of the subwoofer using a single RCA cable (the two jacks on the left in the photo). A 'Y-Cable' may be necessary to connect the LFE output to both the left and right channels of the subwoofer.
2. How to Connect a Subwoofer to Speaker Level Outputs Some receivers and amplifiers do not have an LFE or Subwoofer output. In this case you can use the speaker outputs of the receiver to connect the subwoofer. Using speaker wire, connect the left and right channel speaker outputs of the receiver to the left and right channel speaker level inputs on the subwoofer (the speaker inputs on the right side of the photo). Using speaker wire, connect the left and right channel speaker outputs on the back of the subwoofer to the left and right channel front speakers.
I'm thinking you have an open shield ground on the RCA input side. Connecting speaker inputs possibly restores the ground. Try connecting the high level inputs then disconnect the remote end of the cables (floating the grounds).
Then get out an ohmmeter and find that open circuitor or bad solder joint between RCA ground and real ground in the speaker's amplifier. Or.... if speaker ground kills the hum and you want to use RCA Line Level input to the sub, just connect one minus speaker output on your source amp to one minus on the sub's amp.
It's never a good idea to adapt prescribed connectors to bare speaker wire or vice versa.
Speaker Level and Line Level signals are worlds apart and equipment damage may result. Your Denon (model unknown) probably requires a POWERED SUBWOOFER, to which it would provide Line Level LFE from its Pre Out.
Read the manual where it doesn't say to convert a speaker wire to RCA.
I'm assuming your subwoofer is self-amplified, otherwise it won't work with a preamp (rca) input.
Under Speaker Setup you have to have Subwoofer set to YES (page 16).
If you have good bass-capable main speakers I would recommend setting the subwoofer playback mode to LFE+Main, otherwise just LFE.
Beyond this we would need to know something more about the subwoofer and its controls.
Connect any other preamp out channel, like CDR/Tape OUT, to the sub and tune an FM station to see if the sub is capable of processing audio. A 'normal' audio signal would sound muffled but it would prove the cabling, amp and speaker at least function and point us back to setup as the culprit.
Your receiver should have an RCA connector on the back panel that will be marked "sub woofer" or "LFE out". That connects to your sub woofer with a standard RCA type cable. Also, some powered subs have left and right speaker level inputs and outputs in which you would indeed run the sub woofer through the speaker outputs. The down side of that type of connection is that the line level converter inside the sub woofer will take a slight amount of your receiver's output power, although that is rarely detectable. Also, if you have a Dolby Digital receiver, using this connection method will take away systems ability to accurately control the low frequency effects of a soundtrack.
The problem was that some subwoofers (inluding my velodyne model) cannot process the LFE signals through the line level inputs on its amps, so the other way to run your subwoofer is to run the front left and right speaker outputs from your receiver to the speaker-level inputs on your sub, and then plug your front and left speakers into the soeaker level outputs on the sub. you have to set the onkyo receiver to "Subwoofer: No". that way the LFE signals are sent through the front speaker channels and you will get the same BASS output as if using the line-level input. O So yes it does require a bit more speaker cable, but it works fine now.