Subwoofer Placement Using Measurement

You can equalize a subwoofer to produce a flat frequency response at one position, but that EQ correction will make the response worse at other positions. Room modes create position-dependent peaks and nulls that no amount of EQ can fix because the underlying physics varies throughout the space.

Optimal placement minimizes the variation before EQ is applied. A well-placed subwoofer might have 8-10 dB of variation across the listening area, which EQ can manage. A poorly placed subwoofer might have 20+ dB of variation, which is beyond what EQ can correct without creating new problems.

Open SonaVyx RTA mode and position your phone at the primary listening position. Play pink noise through the subwoofer and capture the frequency response from 20 Hz to 200 Hz. Store this trace. Move the subwoofer to a different candidate position and capture another trace. Compare the two traces to see which position provides smoother, more extended bass response.

Test at least four positions: corner, mid-wall, quarter-wall, and center-wall. For each position, also measure at two or three listening positions to assess how evenly the bass distributes across the room. The best subwoofer position is the one that produces the smoothest average response across all listening positions, not the one that sounds best at a single spot.

Every room boundary (floor, wall, ceiling) provides acoustic loading that boosts low-frequency output. A subwoofer on the floor gets approximately +6 dB compared to free-standing. Against a wall adds another +6 dB. In a corner, all three boundaries contribute up to +18 dB total. This gain is useful for small subwoofers but excites room modes more strongly.

Room modes are resonant frequencies determined by the room dimensions. The first axial mode for a 5-meter dimension occurs at 34.3 Hz (speed of sound divided by twice the dimension). These modes create standing waves with predictable pressure patterns. Placing the subwoofer at a modal pressure maximum excites that mode strongly, while placement at a null minimizes its excitation.

Two subwoofers strategically placed can cancel specific room modes that a single subwoofer excites. Placing two subs at opposite wall midpoints on the same axis cancels the first axial mode along that axis while maintaining output. This "mode cancellation" technique provides 6-10 dB improvement in bass uniformity compared to a single corner-loaded sub.

Measure the combined response of both subwoofers together and individually. Ensure they are in phase by checking that the combined output is louder than either individually across the operating frequency range. If the combined level is lower at certain frequencies, one sub is canceling the other, which can be fixed with delay adjustment or polarity inversion.

After optimizing placement, align the subwoofer crossover with the main speakers. Set the crossover frequency (typically 80-120 Hz) and measure the combined response through the crossover region. Look for a smooth transition without a dip or peak at the crossover frequency.

Use the SonaVyx transfer function to measure phase through the crossover region. Ideally, the subwoofer and main speakers should be within 90 degrees of phase at the crossover frequency. Adjust subwoofer delay and polarity until the phase alignment is optimized, then verify with a combined frequency response measurement.