A question we frequently encounter is which cable (interconnect) should be selected, or more specifically is an RCA Y cable or adapter necessary. This page explains that in most cases, this is in fact not required.
Do I Need an RCA Y Cable or Adapter for my Subwoofer?
It is actually quite common for those setting up a subwoofer to seek an RCA Y cable or adapter for the left and right input connections on the subwoofer. However, in most cases this is actually not the optimum method to set up your subwoofer.
Almost all AV receivers and pre-amps will feature an LFE (Low Frequency Effects) output. The LFE channel is a mono signal and is already filtered before the signal is sent to the subwoofer. Almost all subwoofers will be equipped with an LFE mode. Most will be labelled with LFE next to one of the inputs, which in most cases is the left input. If your subwoofer is not labelled you may need to refer to your user manual for confirmation.
To utilise the LFE channel in the correct manner would mean that you connect a single cable to the LFE input on the subwoofer. You should also dial the crossover control (low pass filter) on the subwoofer to the maximum setting. This is due to the fact that in LFE mode, the AV receiver or pre-amp has already taken care of this for you.
The left and right inputs on a subwoofer are actually designed to receive a full range stereo source. This is when the crossover setting on the subwoofer would need to be calibrated according to the rest of the system environment. In this scenario, the subwoofer can filter out the low frequencies and then pass on the higher frequencies.
In almost all cases, a single RCA subwoofer cable would be the correct choice for your home theatre system.
Why Does my Subwoofer Sound Better When I Use an RCA Y Cable or Adapter?
We often incorrectly associate an increased level in volume as sounding better.
Some subwoofers may indeed display an increased volume output level of 3dB when an RCA Y adapter or cable is implemented.
However, this does not increase the maximum potential output volume of a subwoofer and only serves to bring the subwoofer 6dB closer to clipping the internal preamp and 3dB closer to reaching the dynamic output limit of the subwoofer. The exact same effect can be gained from adjusting the volume control.