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 100Hz. 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 2.5Hz to 20kHz. The measurement setup consisted of SINUS Soundbook quadro (2.3Hz - 22kHz; linear@0dB; ±0.1dB tolerance; 1Hz high-pass enabled), 1/2-inch Preamplifier/Free-Field Microphone (3.15Hz - 20kHz: ±2.0dB; 5Hz - 10kHz: ±1.0dB). Signals were processed with SINUS Driver version 5.1.0.8 and Samurai version 2.0.134. SPL in quiet forest [during 60s: LZ,eq = 49.4dB; LA,eq = 28.7dB(A)] were compared to a quiet university room [during 60s: LZ,eq = 74.4dB; LA,eq = 28.2dB(A)]. Healing properties of felid purrs produced with strong frequencies at an SPL between 30-60dB suggest a general correlation of low-frequency background noise levels and health. Perhaps nature knows better than we do. © 2013 Acoustical Society of America.