Speaker Directivity & Coverage
Definition
Speaker Directivity & Coverage
Speaker directivity describes how a loudspeaker concentrates sound energy in a specific direction rather than radiating uniformly. Quantified as Directivity Index (DI) in dB or Directivity Factor (Q) as a linear ratio, directivity determines coverage angle, throw distance, and rejection of unwanted directions. SonaVyx measures directivity from multi-angle frequency response data.
DI = 10 × log₁₀(Q), where Q = ratio of on-axis intensity to average intensity over all angles
How It Is Measured
Directivity is measured by capturing frequency response at multiple angles around the speaker (typically 0, 15, 30, 45, 60, 75, and 90 degrees horizontal and vertical). SonaVyx computes the directivity index from the ratio of on-axis energy to the spatially averaged energy across all measured angles. The coverage angle is defined as the angle at which the response drops 6 dB below the on-axis level.
Practical Example
A horn-loaded speaker measures +10 dB directivity index at 2 kHz with a 60-degree horizontal coverage angle. This means the speaker concentrates ten times more energy on-axis compared to an omnidirectional source of the same power. The effective critical distance is √10 ≈ 3.2 times farther than an omnidirectional speaker, dramatically improving intelligibility in reverberant spaces.
Coverage Angle
The coverage angle (also called beamwidth) is the angle between the -6 dB points of the speaker's polar response. A speaker with 90° × 60° coverage (horizontal × vertical) maintains useful level within that cone. All speakers narrow their coverage as frequency increases — a speaker with 90° coverage at 1 kHz might narrow to 40° at 8 kHz. Constant-directivity horns are designed to maintain consistent coverage angle across a wide frequency range.
Directivity and Intelligibility
Higher directivity concentrates more energy toward the audience and less toward walls and ceiling, improving the direct-to-reverberant ratio. In reverberant spaces (churches, gyms, airports), highly directional speakers can maintain speech intelligibility where omnidirectional sources would fail. Each 3 dB increase in directivity index doubles the area that can be covered with adequate direct-to-reverberant ratio.
Coverage Design
PA system design matches speaker coverage angles to the audience geometry. A wide 110° speaker suits a short-throw application covering a broad, shallow audience. A narrow 40° speaker suits a long-throw application covering a deep, narrow zone. SonaVyx helps verify installed coverage by measuring frequency response at multiple audience positions and comparing against the design specification.
Try It Now
Measure speaker coverage — free SPL analysis at multiple positions