Spectrograms in decibel scale

What is power level of spectrograms color scale in decibels scale?

In figure below there is color scale with numbers in desibels (ref. 20 uPa)

The algorithm cuts the color scale at 13 dB and 59 dB.

Spectrogram, part 3

In nature, there is also infrasound whose a major source is wind. How infrasound caused by the wind stands out?

In a figure below, a strong ground wind causes noise in the low frequency regions. A particularly strong variation is on very low frequencies, which can be detected best in the time domain measurements. There is no noticeable periodicity in wind-induced infrasound. The figure below shows wraparound point (1.), where there is infrasound caused by strong ground wind.

Infrasound produced by wind turbines can be seen very clearly as vertical stripes pointed by white arrows (2.).

Ground wind means wind near the ground level. It should be noted that even if there is wind in higher level and the wind turbines are in operation, there is not always hardly any wind on the surface of the ground . In the figure above, it can be seen that during . 00: 00 – 14: 00 period there is little wind on the Earth’s surface, but between 14: 00 – 22: 20 wind is blowing hard in the surface of the Earth.

Wind turbine infrasound signal is covered partly by the noise caused by the strong ground wind.

Spectrogram, part 2

Can we be absolutely sure that infrasound in the spectrogram is caused by wind turbines?

In the figure below there is shown side by side, three infra-sound spectrograms measured at various distances on the same day. Measuring distances from the nearest wind turbines are 1.5 km, 2 km and 14 km from left to right.

During the intervals as indicated by the arrows, the closest power plants have been shutted down (dyed green space). Also, after at 9, some shorter shut-downs can be seen.

Wind turbine shut-downs are clearly visible in spectrogram yet 14 km away.

This indicates that the spectral spikes in spectrograms (shown as vertical stripes) which disappear when the plants are stopped, are derived from the plants in question. In spectrograms there can be seen weaker infrasound signal that comes from further located wind power plant.

Spectrogram, part 1

The figure below shows infrasound signal produced by a typical wind turbines. On the horizontal axis there is frequency in Hz 0 – 5 Hz. The vertical axis represents time in hours 00: 00 – 24: 00.

Infrasound strength is described in colors from blue to red. Red is strong signal.

Measurement performed on living spaces. The nearest power plant is approximately 1,37 km. The spectrogram signals the intermittent signals under frequency 5 Hz.


  1. 1. Wind turbine basic blade frequency. This 0,6 Hz.
  2. 2. The second harmonic which is 2 *0,6 Hz = 1,2 Hz.
  3. 3. The third harmonic.
  4. – 8. 4. Higher harmonic frequencies

The following figure shows the same measurement in the 0-20 Hz frequency band.

NOTE! Infrasound frequency range comprised by wind turbines is mainly less than 5 Hz .

The following figure shows the wind turbines stop a little before at 11: 00.

The following figure shows the same measurement in 0-20 Hz band.

The figure below shows measurement results during the same date and from 5 km distance to the same power plant.

The figure above shows the horizontal lines caused by normal housing disturbances, mainly due to closure of the doors.

The following figure shows the same measurement in 0-20 Hz band.

The study start

During the summer 2016 infrasound measurement device development proceeded. Mainly algorithm and user interface development were continued. A measurement instrument prototype was completed in early fall, and it was tested in different parts of Finland.

September – October one party in government took people experienced health problems seriously. The case got a lot of attention in the media. In the past people who were suffering health symptoms caused by wind turbines were stamped to be hypochondria by media and that’s why the politicians had not been able to grasp the point. Finnish National Institute for Health and Welfare was also commissioned report of the topic. Wind turbine harm to health was examined, but not any serous investigation was done. The researchers did not measure the infrasound in any point.

Interest aroused from the potential health hazards of infrasounds, I wonder how objective research should be carried out. Since I have been involved in the past in various research projects related to health and technology, I knew that one of the major risk factor is nocebo effect. If the people themselves are able to see in real time the amount of infrasound by using the measuring device, they may experience symptoms seem to get worse at the moment. Therefore it was goal to make a system, where man himself is not accessible from the measured data, but the opening of the data is done elsewhere.

Upon request, I also did research plan to the Ministry and manufactured a number of measurement instruments for the government planned infrasound and health research. We have not heard anything from Ministry, but we started making research anyway, so that the research could be completed in the target timeframe.

Since January 2017 about 20 infrasound measuring devices have been at a time in different parts of Finland about 1-10 kilometers of power stations in homes, where there have been health symptoms which occurred after wind turbines started. Measuring devices have been in same places a one month. At the same time there was filled a daily health symptom diary.

Survey data are unloaded from the raw data and diaries during the spring.

If infrasound caused by wind turbines are reason to people’s sleep and health symptoms, it appears in the investigation we undertook. We will analyze the results when data has been collected enough, we hope to get data from some hundred test persons.

Infrasound, what is it?

I heard about the infrasound noise generated by wind turbines about two years ago. At the same time I was told that large wind turbines produce infra sound that can reach up to several dozens of kilometers from plants. There were people who claimed that infrasound is hazardous to human and animal health and long-term exposure causes permanent physiological changes.

At first I did not know how the issue should be approached. Does it make sense that wind turbines could be a health risk? I had visited a few times at the foot of wind turbines in the Hailuoto ferry quay and mostly I remember that they took an enormous uproar in high winds. I was told that in addition to audible noise, wind turbines cause infrasound that propagates long distances, and abroad several researchers argued over whether the infrasound from the wind turbines harm people or not. I got to know also a few articles that told about people experiencing adverse health effects, whose cause was considered to be infrasound produced by wind turbines.

In Finland, too, large-scale wind farm areas have been invested and built. After all, wind power is a pollution-free and renewable electric energy production form. How was it possible that the alleged adverse health effects had been ignored and why it had not been adequately tested? Or is the whole concern about infra-sound health-related problems vain, people’s imagination, nocebo?

At previous work positions I have had a lot to study on the effect of placebo and how it can be reduced in medical device trials. The placebo effect is known to be very large and presumably nocebo effect is equally challenging. Placebo treated is improved, even if the medicine would be a sheer limestone tablet, while in nocebo a person gets symptoms of an external factor, which is not scientifically been proven physiological causality symptoms.

Case was bothered me. I heard from my friend that at several locations in Finland, people had begun to experience symptoms similar to those of foreign researchers had reported. They had occurred arrhythmia, hypertension, unexplained nights awakenings, tinnitus and tinnitus in a low frequency.

My friend had also acquired an infrasound measurement device, and was able to measure the wind turbine infrasound. At the same time, he had followed his own symptoms and marked the symptoms to diary. Infrasound he had recorded a monthly basis and compared after months wind turbines infrasound and temporal onset of symptoms in a diary. His findings were that the signs and symptoms of infrasound have connection.

We talked many times how the matter could be studied more extensively. We concluded that we should obtain a sufficiently favorable infrasound measuring equipment, which could measure and record from multiple locations at the same time and at the same time collect information on people experiencing adverse health effects. In the end, we decided to develop own measuring instruments, which we could, if necessary, to carry out the study.

In the spring 2016 we completed the first test device, which can measure the wind turbines produced by the infrasound.