Exploring Infrasound: Understanding Frequencies Below the Audible Range and Their Effects

The human auditory system is a marvel of natural engineering, capable of detecting a vast range of sounds. However, there are certain frequencies that lie outside the perceptible range, particularly those below 20 Hz, known as infrasound. This article delves into the characteristics of infrasound, its perception, and the effects it can have on humans and animals.

How Frequencies Are Perceived by Human Brains

Even when using varying frequencies, humans can hear a wide range of sounds. Above 20 Hz, the brain performs a fascinating phenomenon where the pulses of acoustical energy blend together, creating what we perceive as a 'pitch' or 'note'. However, below 20 Hz, our perception changes dramatically. Below this threshold, individual beats or pulses are perceived distinctly, making the difference between rhythm and melody dependent on frequency. Memory plays a crucial role in this process; if the beats or rhythms are slow (one cycle per minute or more), we do not interpret them as rhythms." "

The frequency at which our brains can connect these pulses is crucial. Only when the frequency of the beats is close enough together in time can our brains interpret them as a rhythm. This threshold is about 20 Hz, the lowest frequency most people can hear. Below this frequency, we lose the perception of melody and rhythm, instead hearing distinct pulses.

Human Hearing Range and Perceptible Frequencies

Humans can typically hear sounds within the frequency range of approximately 20 Hz to 20,000 Hz (20 kHz). The lowest frequency that most people can perceive is around 20 Hz. Frequencies lower than this range, below 20 Hz, are categorized as infrasound, which means 'below sound' in Latin.

Despite its name, infrasound is not entirely out of reach; its effects can be felt physically. Humans generally cannot perceive infrasound through our hearing, but we can experience its physical presence. For instance, infrasound can evoke feelings of unease or anxiety and may cause sensations of pressure or vibrations in our bodies. This is due to the way infrasound interacts with the physical environment and our bodily tissues.

Detection and Abilities of Other Species

While humans cannot hear infrasound, specialized detection equipment can help us understand its presence. Animals such as elephants and whales, which have highly sensitive hearing, utilize infrasound for communication over long distances. This demonstrates the unique acoustic capabilities that some species possess.

For further comparison, let's look at the perception of light and heat in the human body. Light, visible to humans in the range of approximately 380 nanometers to 750 nanometers, is visually perceived. However, frequencies below this range, termed infrared, are outside the visible spectrum and are perceived as heat. The human body can feel infrared light as warmth.

Conversely, heat vibrations in the human body are related to the movement of molecules and can be experienced through thermal sensations. These vibrations do not translate into sound or perception in the same way that infrasound does, emphasizing the distinct nature of these types of sensory inputs.

In sum, while we cannot perceive frequencies below 20 Hz as sound, we can feel the effects of infrasound through physical sensation. These effects, however, do not align with the perceptual experiences of seeing light or feeling heat in the same manner. The world of infrasound remains a fascinating area of study, offering insights into the boundaries of human perception and the remarkable abilities of other species.