If a tree falls in a forest, can you hear it?

Abstract

Anthropogenic noise, from slowly rotating/reciprocating machinery, contributes immensely to environmental low-frequency noise below 100 Hz. This poses an acoustic low-energy problem as our technology offers no effective passive method for remediation. While attention is given to negative impact on human health and ecosystems, we still know and publicly do too little about it. Technical standards in Europe are A-weighted measurements that disregard actual energetic contributions of low frequencies. Different aspects of low-frequency sound have been illuminated by complementing acoustic measurements with findings from technical acoustics, bioacoustics, and human medical science. Sound pressure levels (SPL) were measured from 2.5 Hz to 20 kHz. The measurement setup consisted of SINUS Soundbook quadro (2.3 Hz– 22 kHz; [email protected] dB; ±0.1 dB tolerance; 1 Hz high-pass enabled), 1/2-in. Preamplifier/Free-Field Microphone (3.15 Hz– 20 kHz: ±2.0 dB; 5Hz–10 kHz: ±1.0 dB). Signals were processed with SINUS Driver version 5.1.0.8 and Samurai version 2.0.134. SPL in quiet forest [during 60 s: LZ,eq = 59.3 dB; LA,eq = 29.5 dB(A)] were compared to a quiet university room [during 60 s: LZ,eq = 74.4 dB; LA,eq = 28.2 dB(A)]. Healing properties of felid purrs produced with strong frequencies at an SPL between 30 and 60 dB suggest a general correlation of low-frequency background noise levels and health. Perhaps nature knows better than we do.