Early Reflections

Early reflections bridge the gap between the direct sound and the diffuse reverberant field. They arrive within the first 50-80 ms (sometimes extended to 100 ms for music) and can be individually identified in the impulse response as distinct spikes following the direct sound. Each spike corresponds to a specific reflection path: floor bounce, ceiling reflection, side wall reflection, back wall, and combinations thereof. The Haas effect (precedence effect) governs how we perceive early reflections. Reflections arriving within about 20-30 ms of the direct sound are perceptually fused with it — we hear them not as separate echoes but as added loudness and fullness. This fusion increases the perceived level by up to 6-10 dB without the listener being aware of the reflections as distinct events. This is why a room sounds louder than an anechoic chamber at the same source level. For speech intelligibility, early reflections are beneficial because they reinforce the direct sound energy that carries consonant information. The C50 (clarity for speech) metric is defined as the ratio of energy arriving in the first 50 ms to the energy arriving after 50 ms: C50 = 10 × log₁₀(E₀₋₅₀ / E₅₀₋∞). Higher C50 values indicate better speech clarity. Target: C50 > 0 dB for acceptable intelligibility, > 2 dB for good intelligibility. For music, C80 (clarity for music) uses an 80 ms boundary, reflecting the longer temporal integration for musical perception. Concert hall targets are typically C80 = -2 to +2 dB — a balance between clarity and reverberant envelopment. Lateral early reflections (from side walls) are particularly important for spatial impression in concert halls. They create Inter-Aural Cross-Correlation (IACC) differences that produce a sense of spaciousness and envelopment. This is why concert halls are typically designed with narrow, parallel side walls near the stage. SonaVyx identifies and timestamps early reflections in the impulse response and computes C50, C80, and D50 clarity metrics.