What we don’t hear:

Sonic Weapons, Hypersonic’s and Perceptual Expectations

Our senses have, over a long time, refined themselves to become near perfect sensory receptors. Our eyes, ears, fingers, nose and mouth interprets the world we live in in such a way that our brains translates the information filtered via our own history of personal experiences, to give us our conscience being. However, our senses can be deceived. They can be illusionary and in the case of sound, it is no different. When you hear a sound, what are you actually hearing? Much like how our eyes only receive information from certain types of light (see right), our ears can only hear certain frequencies. So then, what are we not hearing? And what does this mean?

*(As you can see above, we have very little vision in the grand scheme, although maybe it’s for the best…)*

Firstly, you might question why we can only hear within a specific range? Why can’t we hear every frequency of the sound around us? The simple answer is that it’s better for our survival. Much like light, our senses only require a certain amount of specific information for our survival. That happens to be in the visible light part of the spectrum - it doesn’t do us much good if we could see in microwaves or gamma rays as we don’t necessarily require it to avoid a common threat, or as a beneficial thing to see in our daily lives in general. The same works for sound. The frequencies are tuned to the scale of the world that we live in and the air within it. Ultimately, our senses have been fine-tuned to equip us with sufficient (and brilliant) tools for our survival.

*(Image depicting our sonic awareness, with the infrasound and ultrasounds being inaudible to humans.)*

The second thing you might ask, with growing concern is, can these unheard sounds influence me without knowing that it is there? Do they cause any harm, like microwaves or Gamma waves would? You might even take this a step further and ask: can I influence ones emotional or psychological state by playing audio outside of their capable hearing range? If so, what effects can this produce and how legitimate can any experiments even be if tested?

Our bodies are effected by sound in an array of ways and are importantly great conductors of sound. Since it is a universal sense, it’s importance as the first warning tool of imposing danger amongst our species and others have made it a pertinent tool in the game of survival. Physiologically our bodies immediately react to such threats. As cortisol is released, your heartbeat will begin to accelerate, you may begin sweating and you your nerves will be on edge. This bleeds into behaviour, much like how someone might wince at the sound of scratching chalkboard or avoiding loud, uncomfortable sounds. On the other hand, psychologically, it effects our emotions, moods and even our perceptual expectations.

There are plenty of sounds that exist but we don’t have the capacity to hear. A black hole for example, emits the note of a B flat 57 octaves below middle C. Sounds can even be deadly above 200 dB although, this is nothing to worry too much about as it’s (probably) impossible to reach that level of noise. In fact the threshold for experiencing pain is 130 dB and the absolute limit of noise is 194 dB (sustained). The eruption of Krakatoa in 1883, which is considered to be the loudest sound in our recorded history, physically deafening if nearby, could be heard thousands of kilometres away and registered at around 172 dB.

Infrasound, much like the sound we are used to hearing is comprised of vibrations. The difference is in the speed of these vibrations, which in the case of infrasound is much slower than the norm, making the sound too low for our ears to pick up. Interestingly, most objects that can make an audible sound also produce an infrasound which we cannot hear. However, it wasn’t until the 1930’s that Hugo Benioff and Charles Richter revolutionised the research of earthquakes when they realised that even when audible sound isn’t registered, infrasound were in fact being picked up, tiny fluctuations in the atmosphere, dubbed ‘microbaroms’.

The northern lights even emit an infrasound. You might be thinking that I have become crazed and the sounds I am hearing might all be in my head. But, hopefully, you would be wrong. In a way similar to the transposition that occurs when infrasound is sped up to cartoonish squeaks in the sinister rumbling of thunder. Certain wavelengths and frequencies can be transposed to an audible level, for example this volcano. Originally, infrasound found it’s benefits in spying on soviet technologies, to listen for the first bomb by ways of a stratospheric balloon system which was used to monitor upper atmospheres. Much like how the advent of satellite technology brought about the transition moving from weaponised technology to data collection, the same has happened for how we listen to our atmospheres.

An image relating the distance of which the eruption could be heard over the globe.

You may have noticed my mention of weaponised technology. Well, sound can be used as a weapon too (I am not talking about playing Ed Sheehan on a loop, although some may describe that as a form of lethal weapon) - infrasonic weapons, similar to LRAD (Long Range Acoustic Device) rely on a method using low frequency sounds played at an extremely high decibel range. If you were to sit in front of a subwoofer for example and played an extremely low frequency, you would likely be able to see the vibrations of the speaker but not actually hear them. But if the speakers were vibrating at say 19Hz, which happens to be the resonating frequency of your own eyeballs, you would notice that your eyeballs would begin to wobble.

If this Saturday night feeling isn’t exciting enough then you could try increasing volume of said frequency. Now, it could begin to effect your breathing, literally shaking your body and bones leading to nausea and hearing impairments. If you really weren’t fond of someone you might crank that Ed Sheeran track right up to 250Hz and a human head will easily explode (the energy required to power such a noise borders on impossible but never say never!). Now, although these no doubt visceral repercussions of playing such loud, abrasive low-end frequencies can cause a physical damage, what about the more subtle implications of unheard sounds?

Hypersonic’s relates to a phenomenon which was written about by Tsutomu Oohashi and other research colleagues and explores how the addition or removal of certain frequencies can ultimately effect certain phycological or physiological elements of human reaction and behaviour. I should note before getting into it all that this research has come under some scrutiny for it’s subjectiveness, albeit interesting and controversial results. It is contradicted by studies which found that people with good ear and are thus capable of distinguishing high resolution audio (sounds up to 30kHz) couldn’t distinguish between frequencies that could normally be heard overplayed with hypersonic’s. So take this section with a pinch of skeptical salt.

Here is an image of said frequencies. Try to make some sense of it if you can.

That being said, in 2000 in a journal of neurophysiology, researchers described a series of objective and subjective experiments in which subjects were played music which sometimes contained HFC’s (High Frequency Components) above 25kHz and other times there was nothing added. Interestingly, what they found was that despite not being able to consciously tell the difference, when played HFC, they measured enhanced (and statistically significant) alpha wave activity as well as have a personal preference to the HFC-laid sound.

Furthermore, they were unable to detect anything when only ultrasounds (freq. above 24kHz) were played. Demonstrating that when listening to HFC's without a bypass or comparisons they were limited to no results. It get’s really interesting when we start to dive into psychoacoustics. Essentially physchoacoustics state that the ear cannot respond to sounds of that high a freq. - in an air-conducted passageway, like the ear for example - in other words, is there maybe another way that isn’t through air vibration that could be causing these sub-conscience reactions?

A study in 2006 revealed that when presented with either loudspeakers or headphones, the hypersonic effects dud not occur when they were fed through headphones. The same results could not be replicated.There are contradictions within his results. For example they were unable to detect any effects on listeners when on only ultrasonic frequencies were played. The Hypersonic effect was only present when comparing the two variations of bandwidth. Bandwidth limited material was more highly regarded by test subjects when the full bandwidth was played immediately afterwards.

So, the results of Oohashi’s experiment could not be replicated. System non-linearities (present to varying degrees in all audio reproduction electronics, are known to produce lower-frequency intermodulation products when the system is stimulated with high frequency signals. The idea is that this mechanism could produce signals in the audible range of sounds allowing listeners to distinguish the two.

Although Oohashi’s results could be deemed somewhat inconclusive, the idea stands that there may be a potential underlying response to such sounds. It also displays, again in a similar way that light does, that there are elements of sound that still have mysterious components. How might this change the way we behave? Perceive the world around us? Listen to language? Work? Enjoy a Film? How will it effect us as consumers of advertisement?

The idea that certain sounds might be able to prematurely illicit a particular predisposed emotional response to a specific sense, word or song is fascinating. This baiting of our perceptual expectations has the potential to become a threat in the future - much like how it has been in the past, but it could also lead to an entire area of psychology which is yet to be explored. More than anything though I think it’s a light reminder of how limited our experience of the universe is, and the absurdity of it all.

Maybe these can be dealt with by someone who is more knowledgeable than I am in the subject. In fact, I absolutely hope that is the case.