Low-frequency impact sound in CLT floors: Perceptual gains from beam integration

Overview

Cross-laminated timber (CLT) construction exhibits inferior acoustic performance in the low-frequency impact-noise domain, a deficiency inadequately captured by existing single-number rating metrics derived from tapping-machine spectra. This study evaluates the efficacy of beam integration as a structural intervention to attenuate sub-100 Hz impact noise in CLT floor systems through coupled finite-element and room-acoustic modeling with perceptual validation.

Methods and approach

A validated plate-beam finite-element model of a two-story CLT test building was coupled to a rectangular room-acoustic model to generate 12 auralized stimuli representing three slab thicknesses (150, 210, and 270 mm) in both unreinforced and beam-integrated configurations (mid-span and quarter-span placement). Excitation comprised two force profiles derived from literature: jump-type (1.2 kN, 20 ms duration) and run-type (0.6 kN, 30 ms duration) impacts. Frequency-domain responses were converted to time-domain waveforms via inverse fast Fourier transform and presented to 20 normal-hearing adults in a semi-anechoic chamber after full transfer-path equalization. Psychophysical assessment combined magnitude estimation (all stimuli) and paired comparison (jump-type cases). The objective metric employed was event maximum level LAFmax per ISO 717-2:2020 Annex D.

Results

Beam integration reduced LAFmax by 1.9 dB (150 mm slab), 1.3 dB (210 mm slab), and 5.9 dB (270 mm slab), with an aggregate mean reduction of 3.1 dB. Slab thickness demonstrated consistent inverse relationship with perceived loudness across all configurations. Magnitude estimation geometric means exhibited strong correlation with LAFmax (Pearson r = 0.88, semi-logarithmic fit, R² = 0.77), and paired-comparison loudness scaling demonstrated comparable association (r = 0.85, R² = 0.73). The concordance between objective event-level attenuation and perceptual response confirms direct translatability of simulated or rubber-ball test metrics to subjective quietness.

Implications

Beam integration represents an effective structural mechanism for attenuating low-frequency impact noise in CLT systems, with the magnitude of benefit dependent upon slab thickness. The demonstrated strong correlation between LAFmax and human perception establishes this metric as a perceptually grounded design parameter for floor-impact noise evaluation in timber construction. Implementation of event-level metrics in design protocols could address the acknowledged inadequacy of conventional single-number ratings in capturing heavy and soft human impacts below 100 Hz.