Humtones and vibrations
A Short Introduction, Sound and Hearing:
The vibrations of a sound source set surrounding air molecules in motion which in turn results in them being set in motion as well. This is how airborne sound is created.
The airborne sound enters our inner ear via the outer and middle ear, where the sound waves are converted into neuronal impulses. Result: We hear because our brain perceives the air vibrations as sounds.
Airborne and structure-borne sound:
Disturbance of the quiet and noise pollution would not be a problem in residential buildings if sound existed exclusively as airborne sound. If windows and doors remained closed, the occupants would only perceive their own sounds, as no air and thus no sound waves could enter or leave the flat.
However, sound does not only spread through the air, but also in solid bodies. Although airborne sound waves are reflected to a large extent when they hit for instance a solid wall, a small part of the sound also passes into the wall.
The neighbours‘ stereo system turned up loud, for example, will therefore inevitably cause measurable structure-borne sound vibrations in a wall. Airborne sound is converted into so-called structure-borne sound.
Structure-borne sound in walls or other solids can not only be caused by the conversion of airborne sound sources, but also by the direct application of force to a solid. For example by hammering a nail into a wall or by an improperly placed washing machine. If structure-borne sound is generated by walking on a floor or stairs, it is referred to as impact sound.
Very low sound frequencies are perceptible.
For example, the bass of a piece of music resonates not only in walls and floors but also in the human body as structure-borne sound. At high sound pressures, we can therefore not only hear them, but also feel them via mechanical sensors in our skin. At frequencies in the audible range, however, we will always hear the sound through the air before we feel it through the floor.
Vibrating solids, such as walls and floors, set the surrounding air molecules in motion and thus act as sound sources themselves. The loud music of other people living in the house passes through the wall and inevitably also into the air of the neighbouring flats. Since our ears are much more sensitive than the mechanical sensors in our skin, in the vast majority of cases we will first hear structure-borne sound through our ears before we feel it in our bodies (provided that the frequencies are audible).
Physical or Internal Vibrations?
In order to feel actual vibrations caused by structure-borne or airborne sound, very high sound pressure levels must be present because a relatively large amount of energy is needed to make entire houses vibrate. For example, heavy truck or railway traffic would be able to make a house vibrate noticeably. The effects of such vibrations, such as glasses clinking or dishes rattling in cupboards, could be felt by all the inhabitants of a house.
According to a survey among our hum-tone Facebook group, more than 50% of the participants perceive vibrations in their bodies in addition to a hum-tone.
Many assume that the hum-tone they perceive must also be the cause of the vibrations. It is assumed that the building in which the affected persons live is vibrated by sound, which the affected persons can then feel in their bodies.
As already explained in the previous section, very high sound pressure levels would be required to make a building vibrate noticeably. Therefore, one would have to assume that these high sound pressures would be easy to prove by measurements. However, measurements show predominantly low or local sound pressures, which would not be sufficient to explain a vibration of a building. Thus, if no airborne sound with high sound pressure can be measured, a perceptible structure-borne sound in the building can be as good as excluded.
Furthermore, vibration perception does not only occur with hum-tone sufferers, it is also mentioned as a symptom in other diseases.
So we know that vibrations can not only be perceived when something is actually made to vibrate by sound, but that there can also be medical reasons that make affected people feel vibrations in their bodies.
How exactly these connections can be explained medically is still often largely unclear.
There seem to be many similarities among sufferers, both in the perception of the hum-tone and in the perception of vibrations, which point to an internal cause rather than to actually existing hum-tones or real vibrations. Link: low-frequency tinnitus-attributes and characeristics
Infrasound as a Cause of Vibrations?
Infrasound is sound below 16 Hz. It is usually no longer audible tonally and is therefore typically no longer perceived as a pure (humming) sound, but rather as a kind of fluttering.
Due to the hearing threshold of the human auditory system, infrasound is only perceptible at very high levels. Such high levels are very easy to measure.
Extremely high levels of infrasound usually occur when driving a car, travelling by train or flying by plane. It would stand to reason that people who assume that infrasound is causing their symptoms are experiencing considerable stress when using these means of transportation.
As we have now been able to confirm through experiments, affected people with low-frequency tinnitus are often unable to distinguish between a real and an inner hum-tone, since the inner hum-tone is perceived by them as a real sound coming from outside.
It may be similar with the vibration, which many hum-tone sufferers experience. The above explanations may help to better differentiate between real and perceived vibrations.
What evidence is there that the perceived vibrations may have an internal cause?
- Many sufferers report that they experience their vibrations particularly strongly at times when the environment is normally rather quiet, for example in the evening and at night.
- Noise pollution that is actually present does not necessarily also trigger vibrations.
- Other people, even if they are in the same room or sleeping in the same bed, do not perceive the vibrations, even if the affected person describes being literally „shaken awake“.
- Vibrations can vary in intensity from one phase to another without any detectable change in the noise level in the environment.
- Vibrations increase the longer the affected person is physically at rest.
- Vibrations are felt to be particularly strong for example in bed, although a mattress should actually contribute to insulation or decoupling.
- Measurements do not reveal any sound pressures that could produce perceptible vibrations.
- Vibrations are often perceived even if the hum tone is only quiet or non-existent.
- Some sufferers describe a feeling as if a light electrical current were flowing through the body.
- The part of the body where the vibrations are felt is not always the same as the part of the body that touches the floor. The vibrations do not spread through the body as they would if a surface on which one is standing were vibrating. Often the sensation is more of a „wave-like“ spread, left and right sides of the body can be affected differently at the same time.
- Sometimes triggers for the vibrations are described, for example freezers or other appliances, but these only cause vibrations in the sufferers themselves, not in other people.