JL Audio f212 owner manual F. Trim, Polarity, Phase

E.L.F. Trim

The Extreme Low Frequency (“e.l.f. trim”) knob allows the user to apply a certain amount of signal equalization at 25 Hertz (extremely low bass). At full counterclockwise rotation, the signal at 25 Hz is cut by 12 dB. At “0” the equalizer is set flat for zero contribution to the signal. At full clockwise rotation, the signal at 25 Hz is boosted by 3 dB.

The E.L.F. Trim feature is useful for tailoring the Fathom’s very low frequency output for your particular room. Adding some boost can make certain material more exciting. Using the cut function can help to compensate for room or boundary gain in the low frequencies. Room boundaries and the room’s finite (limited) size naturally cause very low frequencies to be boosted relative to other parts of the signal. As such, using the E.L.F. Trim feature to cut the lowest frequencies can help to tame “bloat” or unnatural sounding low bass in small to medium sized rooms (and can also reduce unwanted vibrations in the room or throughout the house).

Polarity

The Polarity switch allows the user to select between normal (0 deg) and reversed (180 deg) signal polarity. The Polarity switch will primarily affect the small frequency range around the crossover point between your subwoofer and satellite speakers.

Unlike the Phase control, which effectively adds time delay, the Polarity switch produces an instantaneous reversal of the signal’s amplitude peaks. For example, if at a given reference point a sine wave has an amplitude peak, by flipping the phase switch you instantly convert that peak into a trough or amplitude dip. Because the effect of the Polarity switch is immediate, it compliments the operation of the Phase control and cannot be replaced by it.

When placing your Fathom in the room, experiment with the Polarity switch before adjusting the “Phase” control. Either position of the Polarity switch may provide a smoother transition between your Fathom subwoofer and the satellite speakers. Use source material with good mid and upper bass content for evaluation.

Phase

The Phase control knob allows the user to adjust the “timing” of the subwoofer output relative to the main speakers. The Phase control will primarily affect the small frequency range around the crossover point between your subwoofer and satellite speakers. The Phase control’s labels are referenced to 80 Hz since this is the most common crossover point between satellite speakers and a subwoofer. Phase settings between 0 degrees (full counter-clockwise rotation) and 280 degrees (full clockwise rotation) are possible.

Speaker, subwoofer, and listening seat positions vary greatly in home theater installations. Since physical positioning of speakers relative to the room boundaries and each other greatly affects the perceived quality of sound output, sometimes it is helpful to delay the subwoofer output. This is exactly what occurs when you turn the Phase control beyond 0 degrees.

Once your Fathom has been placed in your listening room to give you the smoothest overall sound and after you have determined the optimum “Polarity” switch position (see preceding section), experiment with the position of the Phase control. Using familiar source material with good mid and upper bass content, adjust the Phase control and listen for better defined mid-bass and a smoother transition between the subwoofer and satellite speaker systems. If no single setting sounds better than another, leave the Phase control at 0 degrees.

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