Optimal stereo speaker placement : Part II

Optimal stereo speaker placement is an iterative process that involves balancing room acoustics, speaker design specifications and geometric positioning to achieve a flat frequency response and accurate stereo image at the main listening position (MLP).

The placement process can be categorized into establishing foundational geometry, managing wall proximity (especially for bass frequencies), and addressing room reflections.

Managing Wall Proximity and Low Frequencies

Low-frequency placement is dominated by avoiding Speaker-Boundary Interference Response (SBIR), which creates deep cancellation nulls that cannot be fixed by equalization (EQ).

1. Speaker-to-Wall Distance (Front Wall)

The distance between the speaker and the front wall (the wall behind the speaker) must be carefully controlled to manipulate where the cancellation frequency occurs. Placing speakers in the intermediate distance should generally be avoided, as this often results in the worst-case scenario: deep, uncorrectable nulls in the critical mid-bass region (around 70 to 150 Hz).

Optimal strategies include:

Strategy	Goal	Placement	Notes
Boundary Loading	Shift null to high frequency/control bass	Very close to the wall (e.g., 300mm to 1000mm).	This is pragmatic for small rooms. The resulting bass boost (boundary gain) can be corrected using EQ or Boundary Gain Compensation (BGC) controls.
Far Field Separation	Push null below speaker range	Over 2.2 meters (7.3 feet) from the front wall.	Ideal for large rooms, but often impractical in residential settings.
Flush Mounting	Eliminate front wall reflection	Speakers are mounted in the wall.	The only way to completely remove the quarter-wavelength cancellation caused by the front wall.

2. Port Design and Other Boundaries

• Rear-Ported Speakers: If your speaker has a rear-firing bass port, it should be placed at least 2–3 feet (0.6–0.9 meters) away from the wall to prevent low-frequency reflections from causing time-smearing distortion.

• Side Walls: Try to avoid placing speakers too close to the side walls. Maintain equal distance from both side walls for optimal stereo imaging.

• Corners: Avoid placing speakers in the corners, as this is where low-frequency energy accumulates, leading to an exaggerated, unnatural rumble.

3. Subwoofer Placement

Subwoofer placement is primarily governed by the room's standing wave pattern, as low frequencies are omnidirectional.

The recommended empirical method is the "Sub Crawl" technique: place the subwoofer temporarily at the listening position, play a continuous low-frequency tone, and crawl around the room to identify the spot where the bass sounds most uniform and consistent. That spot is the optimal position for the subwoofer.

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