Noise level in household appliances – what it means and why it is important

Several decades ago, any technique was synonymous with the word “noise”. Suffice it to recall the Soviet Volga washing machine or the Cyclone vacuum cleaner, the owners of which put up with the rumble and hum. But progress does not stand still, so now the noise level is one of the main characteristics on which the choice of home appliances is tied. And this topic is worth a separate article – we understand what noise is and how it happens.

The sounds emitted by working equipment are of a different nature . Some we hear, others we don’t notice. Some noises calm us down, some annoy us, and others can have destructive properties for a living organism and even for inanimate objects. The types of noise can be completely different in physical characteristics, but they will necessarily converge in one dimension – in the level of human perception.

The perception of noise depends on the individual’s comfort threshold and the level of irritability. Some people are comfortable with the sound of a petrol trimmer outside, others are enraged by dimensional tick of the second hand of wrist watches . But, if we consider the noise level not as a unit of measurement of comfort, but as a scientific phenomenon, then the loudness of the sound of electronics and technology can be expressed in decibels.

A minute of history
Perhaps any cognitive material begins with the phrase “… was named after an outstanding scientist …” and so on. But no, in the case of noise and its measurement, things are not so simple. Noise was not discovered, therefore, this phenomenon was not named after a famous person. Only a unit for measuring noise was named after the famous American scientist Alexander Bell, founder of AT&T.

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True, the term “bel” was introduced to measure interference in telephone and telegraph lines. It was only later that it began to be used to classify noise level as a perceivable phenomenon. Nowadays, the “decibel”, which is based on the decimal logarithm, is considered to be the measurement unit of noise. Hence, in fact, the prefix “deci”, which means “ten minus the first degree.” By the way about that.

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Logarithmically this is
The decibel is nevertheless closer to mathematics than to physics. If, for example, “hertz” means a cyclical action in time, then “decibels” indicate the degree to which the intensity of what is happening is changing . It is not easy to understand, but we will try to explain, as they say, “on the fingers”.

 

For example, a computer fan runs at maximum speed and makes a noise of about 22 dB. This is an acceptable noise level – it is practically inaudible, and it does not interfere with a comfortable life even at night. Another fan, at the same settings, produces only 10 dB more noise. At the same time, it seems that he makes a noise almost twice as loud. The key word is twice. That is, not “how much louder”, but “how many times louder”.

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It is generally accepted that 0 dB is the minimum that the human hearing perceives. Accordingly, the countdown starts from this value, and with every 10 dB the volume level increases 10 times from the previous one. If you imagine a smooth increase in the noise level on the graph, you will get a parabolic figure. At the same time, at the beginning of the parabola, the increase in power will be practically imperceptible by ear, while by the middle of the figure the same 20 dB will turn out to be a significant increase in both noise and sound pressure.

 

In “x”, the rate of increase in sound power with each dB will look like this:

+3 dB = power x2;
+10 dB = power x10;
+60 dB = power x1000000.
So, the noise level, measured in decibels, increases not linearly, but logarithmically – with each new unit, the sound intensity increases by N times. Example again: a level of 80 dB corresponds to a very loud conversation, and 100 dB is already traffic noise or a jackhammer.

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That is, only 20 dB separates a noisy office from an industrial rumble – this is a noticeable increase in volume. At the same time, the difference between the sound of a ticking clock and a quiet conversation also corresponds to 20 dB. In this case, the difference is no longer critical.

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For an approximate orientation to the ambient loudness levels, experts identify several standard values:

15 dB – rustle of foliage;
20 dB – quiet whisper, 1 m;
35 dB – wall clock ticking;
45 dB – quiet conversation;
60 dB – quiet conversation;
75 dB – loud conversation;
80 dB – vacuum cleaner noise;
90 dB – heavy truck, 7 m;
100 dB – rock music concert;
110 dB – helicopter;
120 dB – jackhammer;
140 dB – takeoff of a jet plane, 25 m;
150 dB – rocket takeoff, 100 m;
160 dB – shot from a gun near the ear.
It turns out that the noise level of a disco (100 dB) will be louder than complete silence (0 dB), not 100 times, but 10,000,000,000 times. Now let’s remember an example with 22 dB and 32 dB fans. With only 10 dB of noise, the second fan will be three times louder than the first.

However, noise levels are only half the battle in learning about the theory of sound perception. Sometimes it is reasonable to pay attention not to decibels, but to the nature of the sound – spectrum and color. Yes, yes, this also happens.

Noise spectrum
Noise characteristics depend not only on the power level, but also on other indicators. For example, from the spectrum in which the noise “sounds”. Certain sounds can be perceived in different ways by a person, not even differing in loudness in dB. For example, at the same volume level (vibration amplitude), sounds with a frequency from 1000 Hz to 4000 Hz are perceived louder than others. There are three categories of noise.

Low-frequency noise – sounds with a frequency of 16 Hz to 300 Hz. A person perceives them as bass or something deaf, oppressive. For example, the hum of a transformer. And they can also be human voices that sound in the range from 85 Hz to 255 Hz.

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Mid-frequency noise – the bulk of the sounds around us, sounding at a frequency from 300 Hz to 800 Hz. For example, at a frequency of 440 Hz, the note “A” of the first octave sounds. Acoustic guitar can sound in this range.

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High frequency noise is anything that sounds in the 800 Hz to 20,000 Hz range. This can be any sound, including the hum of electric motors or the squeak of inverter washing machines.

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There are sounds in the world with lower and higher frequencies, but they are beyond the capabilities of human hearing. Such spectra are called infrasound (less than 16 Hz), ultrasound (over 20,000 Hz) and hypersound (1 GHz to 10 THz). Such “noise” is perceived by a person at the level of internal mechanisms of protection against destruction – ultrasound is capable of destroying living organisms.

Noise color
Unexpectedly, but true – noise can be of different colors. The difference in color shades of noise can be compared to the decomposition of the light spectrum into shades. For example, white is light noise that includes hues from all the colors of the rainbow.

 

A similar process occurs in sound – white sound noise consists of many waves with different frequencies, durations and power levels. In practice, white noise can be heard between radio stations or TV channels on the air – this is the measured hiss of “goose bumps”.

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White noise looks like this:

 

And it sounds like this (listen) .

There are other “shades” of noise as well. For example, pink noise includes waves of the entire frequency spectrum from 20 to 20,000 hertz. The pink hiss is perceived as deeper, velvety. For example, the noise of a summer rain in a tropical forest or the surf.

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The pink noise graph looks like this:

 

And in the reference form, pink noise sounds like this (listen) .

Several years ago, scientists conducted a series of experiments that proved that noise of a certain color helps to fight sleep disorders. Naturally, it turned out to be the pink spectrum. Sometimes this spectrum is referred to as green noise – natural sounds of nature.

 

An even quieter version of white noise is brown. True, the name of the color noise received not by color analogy, but by its physical properties. The sound of this noise spectrum is reminiscent of the “random walk” of particles in Brownian motion. For example, this is the sound of the wind.

This is what the calibrated version of it sounds like (listen) .

There are many more shades of color noise in the world. These are blue, gray and even black noises, which often exist in an artificial form and are rarely found in life. For example, each person perceives gray noise in a different way due to the way the membrane is calibrated – in medicine, it is used to treat hearing disorders. And black is vacuum silence.

Decibel decibel strife
The above noise characteristics also apply to the “sound” of household appliances and computer electronics. Therefore, when choosing a product according to the noise level, it is necessary to focus not only on decibels, but also on other indicators. For example, everyone understands that a computer fan itself works silently, and the noise comes from the reactive interaction of the blades with air.

But the loudness of the work of external units of some climate systems can be equal to the unbearable roar of aircraft engines. It should be understood that the noise level of an air conditioner consists not only of noisy air flow, but also includes parasitic sounds from compressor vibrations, the hum of a powerful fan. Therefore, when choosing household appliances and electronics in terms of noise level, these factors must also be taken into account.