Placing Free-standing Loudspeakers with Subwoofer - Tip 3Using a subwoofer with the crossover filter (typically at 85 Hz) between the loudspeakers and the subwoofer can improve the monitoring system. The high-passed loudspeakers (sometimes called ‘satellites’) do not reproduce low frequencies. They can now be placed at the walls more freely at distances where low frequency notching does not occur in their pass-bands.
The ‘acceptable’ distance extends now out to 1.1 m. The loudspeakers can be placed even further away (1.1…2 m) without seriously compromising the sound quality. The ‘satellite’ loudspeakers should not be placed too far from the subwoofer (max. distance 2 m). If the distances are larger the tonal balance between the various loudspeakers playing with the subwoofer may differ considerably due to differing excitation of the room modes. In practice free standing loudspeakers always suffer from some irregularities in their frequency responses, usually caused by cancellations.
Figure 1 - Distances from a single wall to the front baffle of the loudspeakers combined with subwoofer(s). Correct (green), acceptable (orange) and avoid (red).
Placing the Subwoofer in the RoomOne common location for the subwoofer is in the front middle of the room, equidistant from the sidewalls. This position is often problematic and compromises the acoustical performance. The subwoofer sits in the first pressure minimum of the lateral standing wave. The frequency response for a subwoofer in that location will most likely display serious irregularities.
The recommended positions for subwoofer(s) are on the floor close to the front wall (max distance from a wall is 60 cm) and slightly offset from the middle of the room to avoid the first pressure minima position, or in a corner close to both the front and side walls. The latter position maximizes the subwoofer efficiency due to corner loading but may also excite strongly the axial modes in the room. Both solutions eliminate the most likely sources of cancellation dips in the subwoofer response.
Remember that the adjustments of gain (input sensitivity) and frequency response (Bass Roll-off) in a subwoofer are necessary during the final in-situ calibration. The acoustical loading must be compensated for. Crossover phase adjustment is also important to achieve and maintain flat frequency response across the crossover region.