Subwoofer LFE Vs. Variable
- Many subwoofers incorporate an LFE RCA input on the amplifier on the back of the amplifier. This is the ideal option when using a receiver that performs crossover and phase adjustment automatically. Room calibration software found in most modern receivers and processors does just that. Alternately, the RCA jacks on the back are simple RCA connections that rely on the user to adjust the variable crossover control. Finally, stereo receivers may force the use of a speaker wire connection between the receiver and subwoofer, since these units can't decode digital surround formats. Step one, therefore, is to determine this relationship between receiver and subwoofer.
- LFE, or Low Frequency Effects, is a dedicated track on DVD and Blu-ray discs. These are devoted to providing nothing but the lowest frequencies. When referring to surround formats, the LFE track is the ".1" in 5.1 and 7.1 audio. Additionally, most modern surround receivers perform bass management internally. Using the LFE input on a subwoofer bypasses the variable crossover entirely, leaving only the volume control in play. This is generally a superior solution not only from a convenience perspective, but fidelity as well. Since the signal is direct from the source to the sub, the signal encounters fewer passive filters along the way. LFE is only found on digital surround formats.
- Connecting the subwoofer preout on a receiver or preamplifier to a subwoofer utilizing standard left and right RCA jacks takes a slightly different approach. In surround sound environments, the variable crossover is normally turned all the way to the right to its highest setting. This effectively avoids the crossover adjustment made in the surround receiver, which in most cases is 60 to 80 hertz. In music systems that send an unfiltered full-range signal to the subwoofer, you must manually adjust the variable crossover control to blend the main speakers to the subwoofer. Knowledge of the main speaker's bass capabilities is required, since you want a minimum of overlap between them and the subwoofer to avoid bloated bass.
- When older surround or any stereo music systems lack dedicated subwoofer RCA preouts, it is necessary to use speaker wire to interface between the receiver and sub. Since the signal is full-range from the main speaker terminals on the receiver to the subwoofer, the variable crossover comes into play, along with the need to manually blend the main speakers and subwoofer. The process is identical to when using an unfiltered RCA-style connection between receiver and subwoofer.