All kinds of electromagnetic waves are hovering around us all the time, which may damage our health at any time. As long as the appliance is in the state of operation, there is electromagnetic field or electromagnetic radiation around it. For example, sound radiation, then how to prevent sound radiation? Small series to popularize the relevant electrical safety knowledge for you.

How sound works

Sound refers to other sounds besides human language and music, including the sounds of natural environment, animals, machines and tools, and human actions.

The sound system includes power amplifier, peripheral equipment (including voltage limiter, effector, equalizer, VCD, DVD, etc.), loudspeaker (speaker, loudspeaker), mixer, microphone, display equipment, etc.

Before we understand the sound radiation, let’s first understand the working principle of the sound box, the medium resonance mixed sound, and the sound production principle. We use the vibrator vibration sound + paper tympanic membrane speaker sound. We often use the sound people all know that the general sound except professional sound, the general general sound bass is not enough, and the general volume of the good bass is not small, which is mainly due to the following reasons Because the size of the sound unit has a great influence on the sound produced by the loudspeaker, many multimedia sound systems directly use subwoofer and external speakers to fully expand the volume range of the sound unit. However, this has a great limit on the appearance of the sound system. This is why the sound systems we see in the market are generally square, square and angular The bass effect is not very good either.

Does the stereo radiate?

First of all, it can be clearly said that most of the audio does not have wireless electromagnetic radiation.

The essence of sound is a low-frequency power amplifier. The maximum frequency of amplified signal is generally 20kHz, and its output voltage will not exceed tens of volts. This frequency is one order of magnitude less than the frequency of electromagnetic radiation (less than 1 / 10).

Because of the low frequency of sound, low frequency electromagnetic wave can only be transmitted by wire. Even if the conductor leaks electromagnetic signal in the process of transmitting alternating current, its radiation energy is far less than microwave oven, induction cooker, TV, vacuum cleaner, hair dryer, mobile phone and other common electrical and electronic products.

Individual audio uses switching power supply, if the switching power supply is not good, it will produce high-frequency electromagnetic radiation, and class D power amplifier is a digital signal processing, its processing frequency is much higher than 20kHz, it may produce some electromagnetic radiation, but there are not many power amplifiers on the market, and there are generally filtering devices inside to remove this high-order harmonic.

Is sound radiation harmful to the body?

Speaker is the terminal of the whole sound system, its function is to convert audio power into corresponding sound energy, and radiate it to space.

It is an extremely important part of the sound system, because it bears the key task of transforming electrical signals into sound signals for people’s ears to listen directly. It has to deal with people’s hearing directly, and people’s hearing is very sensitive, and has a strong ability to distinguish the timbre of complex sounds.

For the speaker, more magnetic fields are concentrated in the low frequency (50 Hz), so we need to refer to the green number, 5ut / 0.05 kHz = 100. If the test value exceeds 100, it means that it is a great risk to human health. In addition, the frequency of the power supply changes from 50 Hz to 200 kHz after passing through the switch tube, so it is necessary to refer to the value of the purple part, 0.92 ut / 0.2 MHz = 4.6. If the test value exceeds 4.6, it indicates that it is a great risk to human health.

Let’s start the test: first, adjust the volume to 60%. After testing the magnetic flux density of the front of a single satellite box, we can see that the current value is 7.85, which is far from the hazard value of 100 that we provided.

The magnetic flux density on the front of the satellite box

Keep a certain distance from the speaker, and the test value drops to 0.01ut

For multimedia speakers, this distance can be maintained in daily life, so the radiation can be ignored.

The magnetic flux density of the reverse phase hole behind the satellite box is 7.53ut

The magnetic flux density around the speaker will change with the increase / decrease of sound. When the sound increases, the flux density increases; when the sound decreases, the flux density decreases.

Next is the magnetic flux density test on both sides of the subwoofer. From the photo below, we can see that the magnetic flux density on the side with phase inversion hole is 12.03ut, which is also the highest value in the test, but it is far from the risk value of 100, which is harmful to human health.

Phase inversion hole of subwoofer

Other side test

On the other side, there is only 6.23ut without phase inversion hole. The radiation impedance characteristic curve of the inverted subwoofer is straighter than that of the loudspeaker before packing. The resonant peak of the loudspeaker is absorbed, and two small humps appear on both sides of the original resonant frequency, and the frequency of the low frequency part is extended downward.

It’s only 6.76ut on the back of the subwoofer

The test of power amplifier is 4.65ut

After all-round testing of this speaker, we can find that the magnetic flux density of the subwoofer’s inversion hole is the largest, up to 12.03. However, this value is far from the risk value of 100.

Therefore, we can draw a conclusion: under normal use, the risk value of magnetic flux density in all directions is far lower than the “safety standard for the general public in electromagnetic fields” published by the European Union, which will not cause harm to human body.

How to prevent sound radiation?

Baibai safety net suggests that although the speaker is small, the radiation is not small. It’s better to be more than half a meter away from the human body to protect hearing and health. In addition, the better the bass effect of the speaker, the stronger the radiation pollution, which needs to be carefully considered when purchasing.

Do not put the sound on the head of the bed, long-term exposure to sound radiation will make people’s sleep quality worse.

In particular, pregnant women, the elderly, children try to reduce the frequency of using speakers, so as not to cause harm to themselves.

Of course, we can also use some electromagnetic radiation protection products: pregnant women’s radiation protective clothing, radiation resistant vest, radiation resistant shirt, radiation resistant apron, radiation resistant screen, radiation resistant glasses, etc., which can not only avoid sound radiation, but also resist other electrical radiation.

It can be seen from the above that in the current environment full of electromagnetic waves, the electromagnetic radiation of the sound has little impact on the human body. We can use it safely. The most important thing is to know how to reasonably place the sound and control the volume.

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