Subwoofer crossover, phase and level: a setup guide

Know where the filtering happens

Before turning a crossover control, verify the connection route. Determine which component low-pass filters the subwoofer signal and whether anything high-pass filters the main speakers. The low-pass reduces higher frequencies sent to the sub; the high-pass reduces lower frequencies sent to the mains.

Genelec's bass-management guide shows that those functions can live in different components. Adding a parallel subwoofer does not necessarily filter the main speakers. Conversely, a system with upstream bass management may call for bypassing a filter in the sub itself. Follow the documented route rather than enabling or bypassing filters solely because of a socket label.

The separate LFE channel used by some film formats is not the same thing as the crossover between stereo main speakers and a subwoofer.

Understand the controls you have

• Low-pass frequency: sets the nominal transition region for the sub's upper output, not a brick-wall stopping point.
• Filter slope: affects how progressively the output falls away, where adjustable.
• Level: changes the subwoofer's contribution relative to the mains.
• Polarity: reverses signal polarity where that control is provided.
• Phase or delay: changes the relationship between contributions using the device's particular implementation.

The SVS SB-1000 Pro manual documents these as distinct controls. A polarity reversal is not generally equivalent to an arbitrary time delay, and a phase control does not guarantee perfect alignment at every frequency. Your equipment may expose only some controls.

Use a repeatable listening sequence

1. Save a baseline

Write down the connection mode, active filters and current settings. Mark feasible main-speaker, subwoofer and seat positions. Respect equipment clearances and use a modest playback level. This gives you a known arrangement to restore.

2. Choose an initial overlap

Use the main speaker and subwoofer documentation to choose a region where both can contribute usefully. A main speaker's published response is a starting clue, not a measured crossover at your seat. Genelec's placement guidance treats subwoofer location and phase integration together; its model-specific crossover values should not be imported into every system.

There is no universal 80 Hz setting. Record the actual frequency and slope where available, including any upstream filters.

3. Adjust the combination

Start with a conservative sub level. At the usual seat, compare the combined sound using familiar recordings with varied bass content. Adjust the available phase or polarity control according to the manual, changing one control at a time. Revisit level and overlap afterward because these settings interact.

Aim for a useful, reasonably even transition rather than the largest bass increase. Listening can expose an obvious imbalance, but cannot certify a flat response or precise time alignment. Avoid prolonged loud test tones.

4. Check the listening area

Recheck other relevant seats and several recordings. If a persistent dip or boom remains, investigate the positions of the sub, mains and listener. More gain or a large equalizer boost is not a dependable cure for cancellation. Room acoustics basics explains why the result changes with position.

Keep the best practical compromise and record what it improved. If a change is uncertain, restore the baseline before making another.

Optional: add measurements

For measured comparison, use a suitable microphone and its calibration information on a stable support. Keep the position, playback settings and relevant processing unchanged while comparing the main speaker alone, the sub alone and their combination. Use supported muting or power-down procedures to isolate them; never disconnect live speaker wires.

REW's Getting Started guide explains both the position-specific nature of a measurement and the need for a timing reference when comparing phase or delay across separate measurements. An unreferenced USB-microphone sweep does not justify a precise cross-measurement delay claim. Use the calibration file appropriate to the microphone's orientation.

Keep a compact settings log

• Arrangement: date, main-speaker positions, sub position and listening seat.
• Signal route: input mode, filter locations and main high-pass status.
• Controls: low-pass frequency and slope, level, polarity, phase or delay, and correction preset.
• Measurement conditions, if used: microphone, calibration, position and timing reference.
• Result: observation, what changed, and whether you kept or reverted it.

This makes the setup repeatable when furniture, speaker positions or equipment change. It also keeps a single impressive recording or trace from becoming the only basis for the settings.