Evaluation of low-frequency façade insulation down to 20 Hz; measurement of low-frequency façade insulation down to 20 Hz and subjective assessment of synthesized cruise ship noise

Abstract

Low-frequency noise has become a growing concern due to its potential adverse effects on human health. However, existing measurement standards and calculation software typically do not cover frequencies below 50 Hz, despite the human hearing threshold extending down to 20 Hz. The knowledge gap regarding sound insulation in the lower frequency range has prompted the need for further research. Recent regulations allow for industrial noise to exceed permissible levels near dwellings as long as indoor requirements are met, creating opportunities for construction in previously unsuitable areas. An example of such a location is Värtahamnen in Stockholm, where cruise ships regularly dock and generate noise from their ventilation systems and onboard electricity generation. These ships are expected to produce low-frequency noise that may pose challenges for nearby planned dwellings. This raises questions about evaluating low-frequency sound insulation and establishing reliable measurement methods, considering that sound pressure levels within rooms can vary significantly due to room modes. This thesis utilizes a field-tested measurement method to assess the sound insulation of façades down to 20 Hz. The measurements also include a subjective assessment of synthesized cruise ship noise and its perception by the auditory system. Additionally, a finite element model was utilized to analyze room modes and gain further insights into their influence on the acoustic environment. The results of the measurements indicate that common façade structures exhibit a moderate sound insulation capability down to 20 Hz. Among the various parameters that affect sound insulation below 100 Hz, room modes and windows were found to have the most significant impact. The subjective assessment revealed that when the synthesized cruise ship noise is barely audible in the receiving room, its frequency contents below 80 Hz lie below the human hearing threshold; however, as the noise levels increase to the point of being disturbing, this frequency limit is lowered to 31,5 Hz. These results indicate that modern façades may have adequate sound insulation below 50 Hz considering the human hearing threshold. However, achieving this requires careful planning and construction.