Indoor extension of an inverse acoustic SPL model: a direct-reverberant field correction for multi-pattern construction noise

Abstract

Construction-noise propagation models are typically formulated and validated outdoors, under free-field (FF) conditions, and for a single temporal noise pattern (most often impulsive pile-driving noise). Neither assumption holds for construction and renovation work carried out inside occupied buildings, where reflected sound energy accumulates in the enclosed volume and the operating equipment may be steady, fluctuating, intermittent, or impulsive. This study extends a previously validated outdoor inverse acoustic sound pressure level (SPL) model, based on FF spherical spreading, to indoor conditions by superposing a direct and a reverberant sound field, and tests the extended model against four canonical construction-noise temporal patterns (constant, fluctuating, intermittent, impulsive) reproduced from real recordings and measured simultaneously at five synchronized receiver positions (0.1–6 m) in an enclosed conference hall. The FF model, applied unmodified indoors, showed systematic near-field under-prediction and far-field over-prediction (mean absolute error, MAE, 3.7–6.4 dB), the signature of an unmodelled reverberant field. The direct–reverberant model removed this systematic bias and reduced in-sample MAE by 63–70% and out-of-sample (leave-one-receiver-out) MAE by 56–66%. The fitted effective room constant was physically consistent and source-independent for temporally continuous sources (implied mean absorption coefficient ᾱ ≈ 0.28–0.30, plausible for the hall's construction), but not for the sparse-duty-cycle intermittent source, for which the reverberant field evidently had insufficient time to establish. Counter-intuitively, recovering distance from SPL alone was less accurate with the better-fitting reverberant model than with the FF baseline, because the fitted critical distances (0.57–1.90 m) place most of the measured range in the reverberant-dominated, distance-invariant zone. The results indicate that indoor construction-noise assessment requires an explicit reverberant-field correction, that this correction depends on the source's temporal duty cycle, and that improved level-reconstruction accuracy does not, by itself, imply improved acoustic localization accuracy indoors.