The level of noise intensity, expressed in decibels, does not take into account such a physiological feature of hearing as different sensitivity to sounds of different frequencies. Therefore, the concept of loudness level was introduced with the unit of measurement background. The loudness level in the backgrounds is determined by comparing the evaluated sound with the sound of the same perceived loudness with a frequency of 1000 Hz (reference tone). In other words, for a sound with a frequency of 1000 Hz, the loudness in the backgrounds is equal to the loudness in decibels:
For example, if a sine wave with a frequency of 100 Hz creates a sound pressure of 60 dB, then by drawing straight lines corresponding to these values on the diagram, we find at their intersection an isophon corresponding to a loudness level of 50 phon. This means that this sound has a volume level of 50 phon.
Dream
The dream scale is a subjective assessment scale developed as a result of numerous tests. The estimates obtained experimentally show that loudness increases as the cube root of the sound intensity, that is, the dependence of the psychological assessment of loudness (J) on the physical intensity (power) of sound (I) is described by the formula:
where k is a frequency-dependent coefficient.
1 dream corresponds to the loudness of a pure tone with a frequency of 1000 Hz with a level of 40 dB. With an increase in the level for every 10 dB, the volume value in sones doubles.
| Sound | Volume, sones | Volume level, backgrounds |
|---|---|---|
| Hearing threshold | 0 | 0 |
| Rustling leaves | ~ 0,02 | 10 |
| Whisper | ~ 0,15 | 20 |
| The ticking of the clock | ~ 0,4 | 30 |
| Quiet room | ~ 1 | 40 |
| Quiet street | ~ 2 | 50 |
| Talk | ~ 4 | 60 |
| Noisy street | ~ 8 | 70 |
| Level hazardous to health | ~ 11,31 | 75 |
| Pneumatic hammer | ~ 32 | 90 |
| Subway train | ~ 64 | 100 |
| Loud music | ~ 128 | 110 |
| Pain threshold | ~ 256 | 120 |
| Siren | ~ 512 | 130 |
| Rocket launch | ~ 2048 | 150 |
| Deadly level | ~ 16384 | 180 |
| Noise weapon | ~ 65536 | 200 |
Noises can have different frequencies and intensities.
Sound propagation speed
Noise travels at a much slower speed than light waves. The speed of sound in air is approximately 330 m / s. In liquids and solids, the speed of propagation of noise is higher; it depends on the density and structure of the substance.Example: the speed of sound in water is 1.4 km / s, and in steel - 4.9 km / s.
Noise frequency
The main noise parameter is its frequency(number of vibrations per second). The unit of measurement for frequency is 1 hertz (Hz), which equals 1 sound wave vibration per second.Human hearing picks up frequency fluctuations from 20 Hz to 20,000 Hz. During the operation of air conditioning systems, the frequency spectrum from 60 to 4000 Hz is usually taken into account.
For physical calculations, the audible frequency band is divided into 8 wave groups. In each group, the average frequency is determined: 62 Hz, 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2 kHz, 4 kHz and 8 kHz. Any noise is decomposed into groups of frequencies, and you can find the distribution of sound energy at different frequencies.
Sound power
Sound power of any installation - this is the energy that is released by the installation in the form of noise per unit of time. It is inconvenient to measure the strength of the noise in standard power units, because the spectrum of sound frequencies is very wide, and the power of sounds differs by many orders of magnitude.Example: the power of noise when air enters a room under low pressure is equal to one hundred billion watt, and when a jet plane is taking off, the noise power reaches 1000 W.
Therefore, the sound power level is measured in logarithmic units - decibels (dB). In decibels, the strength of the noise is expressed in two- or three-digit numbers, which is convenient for calculations.
The sound power level in dB is a function of the ratio of the power of sound waves near the noise source to the zero value W 0, equal to 10 -12 W. The power level is calculated using the formula:
L w = 10lg (W / W0)
Example: if the sound power near the source is 10 W, then the power level is 130 dB, and if the sound power is 0.001 W, then the power level is 90 dB.
Sound power and power level are independent of the distance to the noise source. They are related only to the parameters and operating mode of the installation, therefore, they are important for the design and comparison of various air conditioning and ventilation systems.
The power level cannot be measured directly, it is determined indirectly by special equipment.
Sound pressure level
Pressure level sound L p is the perceived intensity of the noise, measured in dB.L p = P / P0
Here P is the sound pressure at the measured place, μPa, and P 0= 2 μPa - reference value.
The sound pressure level depends on external factors: distance from the installation, sound reflection, etc. The simplest form is the dependence of the pressure level on the distance. If the noise power level is known L w, then the sound pressure level L p in dB at a distance r (in meters) from the source is calculated as follows:
L p = L w - lgr - 11
Example: The sound power of the refrigeration unit is 78 dB. The sound pressure level at a distance of 10 m from it is: (78 - lg10 - 11) dB = 66 dB.
If the sound pressure level is known L p1 on distance r1 from the noise source, the sound pressure level L p2 on distance r2 will be calculated like this:
L p2 = L p1 - 20 * log (r2 / r1)
Example: The sound pressure level at a distance of 1 m from the unit is 65 dB. Then the sound pressure level at a distance of 10 m from it is: (65 - 20 * lg10) dB = (65 - 20) dB = 45 dB ..
In general, in an open space, the sound pressure level decreases by 6 dB when the distance to the noise source increases by 2 times. In a room, dependence will be more difficult due to the absorption of sound by the floor surface, sound reflection, etc.
Noise volume
Human sensitivity to sounds of different frequencies is not the same. It is maximum for sounds with a frequency of about 4 kHz, is stable in the range from 200 to 2000 Hz, and decreases at a frequency of less than 200 Hz (low-frequency sounds).The volume of the noise depends on the strength of the sound and its frequency. The loudness of the sound is estimated by comparing it with the loudness of a simple sound signal with a frequency of 1000 Hz. The level of sound intensity at 1000Hz, as loud as the noise being measured, is called the loudness level of that noise. The diagram below shows sound intensity versus frequency at constant volume.
At a low volume level, a person is less sensitive to sounds of very low and high frequencies. At high sound pressure, the sensation of sound develops into a painful sensation. At a frequency of 1 kHz, the pain threshold corresponds to a pressure of 20 Pa and a sound power of 10 W / m2.
Equal loudness curve diagram
Noise characteristics of equipment
The noise characteristics of the equipment are presented in the form of tables, which contain:- noise power level in dB by frequency bands
- general sound pressure level
Summation of noise sources
The noise from multiple sources does not correspond to the sum of the noise from each source separately. For two installations adjacent to each other, the noise is determined as follows:- If the noise level indicators are the same, then the total noise level is 3 dB higher than the noise level of each installation.
- If the difference in noise levels exceeds 10 dB, the total noise level is equal to the value of the larger of the two noises.
For example, the total noise from two installations with levels of 30 and 60 dB is 60 dB.
- If the difference in noise levels is not more than 10 dB, use the table below. We calculate the difference in noise levels of installations.
If there are more than two noise sources, the calculation method does not change, and the sources are considered in pairs, starting with the weakest.
For example, there are four settings with noise levels of 25 dB, 38 dB, 43 dB and 50 dB.
First, we calculate for the two weakest settings: 38 - 25 = 13 dB. The difference is more than 10 dB, and this setting is not taken into account at all.
For 38 and 43 dB settings: 43 - 38 = 5 dB, the correction from the table is 1.2 dB. The total noise of the three settings: 43 + 1.2 = 44.2 dB.
Now let's find the total noise of all installations. 50 - 44.2 = 5.8 dB. Rounding off the difference in noise levels to 6 dB, we find a correction of 1.0 dB from the table.
So, the total noise level of the four installations is 50 + 1 = 51 dB.
By sound mechanical vibrations of particles of an elastic medium (air, water, metal, etc.), subjectively perceived by the organ of hearing. Sound sensations are caused by vibrations of the environment occurring in the frequency range from 16 to 20,000 Hz. Sounds with frequencies below this range are called infrasound, and above them - ultrasound.
Sound pressure- variable pressure in the medium due to the propagation of sound waves in it. The magnitude of the sound pressure is estimated by the force of the action of the sound wave per unit area and is expressed in newtons per square meter (1 N / square meter = 10 bar).
Sound pressure level- the ratio of the sound pressure value to the zero level, for which the sound pressure n / square meter is taken:
Sound speed depends on the physical properties of the medium in which mechanical vibrations propagate. So, the speed of sound in air is 344 m / s at T = 20 ° C, in water 1,481 m / s (at T = 21.5 ° C), in wood 3,320 m / s and in steel 5,000 m / s. sec.
Sound intensity (or intensity)- the amount of sound energy passing per unit of time through a unit of area; measured in watts per square meter (w / m2).
It should be noted that the sound pressure and sound strength are related to each other by a quadratic relationship, i.e., when the sound pressure increases by 2 times, the sound power increases by 4 times.
Sound power level- the ratio of the strength of a given sound to the zero (standard) level, which is taken as the strength of sound W / m2, expressed in decibels:
Sound pressure and sound intensity levels, expressed in decibels, are the same in magnitude.
Hearing threshold- the quietest sound that a person can still hear at a frequency of 1000 Hz, which corresponds to sound pressure N / m2.
Sound volume- the intensity of the sound sensation caused by a given sound in a person with normal hearing Loudness depends on the strength of the sound and its frequency, changes in proportion to the logarithm of the sound strength and is expressed by the number of decibels by which the given sound exceeds the sound intensity taken as the hearing threshold. The unit of measurement for loudness is the background.
Pain threshold- sound pressure or sound intensity perceived as a painful sensation. The pain threshold is little dependent on frequency and occurs at a sound pressure of about 50 N / m2.
Dynamic range- the range of sound volumes, or the difference in sound pressure levels between the loudest and quietest sounds, expressed in decibels.
Diffraction- deviation from the rectilinear propagation of sound waves.
Refraction- a change in the direction of propagation of sound waves caused by differences in speed on different parts of the path.
Interference- addition of waves of the same length arriving at a given point in space along several different paths, as a result of which the amplitude of the resulting wave at different points turns out to be different, and the maxima and minima of this amplitude alternate with each other.
Beats- interference of two sound vibrations that differ little in frequency. The amplitude of the oscillations arising in this case periodically increases or decreases in time with a frequency equal to the difference between the interfering oscillations.
Reverberation- residual "after-sound" in closed rooms. Formed due to multiple reflections from surfaces and the simultaneous absorption of sound waves. Reverb is characterized by a period of time (in seconds) during which the sound intensity decreases by 60 dB.
Tone- sinusoidal sound vibration. The pitch is determined by the frequency of the sound vibration and increases with increasing frequency.
Main tone is the lowest tone produced by the sound source.
Overtones- all tones, except for the main one, created by the sound source. If the frequencies of the overtones are an integer number of times the frequency of the fundamental tone, then they are called harmonic overtones (harmonics).
Timbre- "color" of the sound, which is determined by the number, frequency and intensity of overtones.
Combination tones- additional tones arising from the nonlinearity of the amplitude characteristics of amplifiers and sound sources. Combination tones appear when the system is exposed to two or more vibrations with different frequencies. The frequency of the combination tones is equal to the sum and difference of the frequencies of the fundamental tones and their harmonics.
Interval- the ratio of the frequencies of the two compared sounds. The smallest discernible interval between two adjacent musical sounds (each musical sound has a strictly defined frequency) is called a semitone, and a frequency interval with a 2: 1 ratio is called an octave (a musical octave consists of 12 semitones); an interval with a ratio of 10: 1 is called a decade.
In this article, you will learn what sound is, what its lethal volume is, and its speed in air and other environments. We'll also talk about frequency, encoding and sound quality.
Let's also look at sampling, formats and sound power. But first, let's define music as an ordered sound - the opposite of a disordered chaotic sound that we perceive as noise.
- these are sound waves that are formed as a result of vibrations and changes in the atmosphere, as well as objects around us.
Even during a conversation, you hear your interlocutor because he affects the air. Also, when you play a musical instrument, whether you hit a drum or pluck a string, you are producing vibrations of a certain frequency, which produces sound waves in the surrounding air.
Sound waves are ordered and chaotic... When they are ordered and periodic (repeated after a certain period of time), we hear a certain frequency or pitch.
That is, we can define the frequency as the number of repetitions of an event in a given period of time. Thus, when sound waves are chaotic, we perceive them as noise.
But when the waves are ordered and periodically repeated, then we can measure them by the number of repeating cycles per second.
Audio sampling rate
The audio sampling rate is the number of measurements of the signal level in 1 second. Hertz (Hz) or Hertz (Hz) is a scientific unit of measurement that determines the number of times an event repeats per second. We will use this unit!
Audio sampling rate You have probably seen such an abbreviation very often - Hz or Hz. For example, in equalizer plugins. In them, the units of measurement are hertz and kilohertz (that is, 1000 Hz).
Typically, a person hears sound waves from 20 Hz to 20,000 Hz (or 20 kHz). Anything less than 20 Hz is infrasound... Anything over 20 kHz is ultrasound.
Let me open the EQ plugin and show you what it looks like. You are probably familiar with these numbers.
Sound frequencies With the equalizer, you can attenuate or boost certain frequencies within the human-audible range.
A small example!
Here I have a recording of a sound wave that was generated at 1000 Hz (or 1 kHz). If we zoom in and look at its shape, we will see that it is correct and repetitive (periodic).
Repetitive (periodic) sound wave In one second, a thousand repeating cycles occur here. For comparison, let's look at a sound wave, which we perceive as noise.
Disordered sound There is no specific repetitive frequency. There is also no specific tone or pitch. The sound wave is out of order. If we look at the shape of this wave, we can see that there is nothing repetitive or periodic in it.
Let's move on to the more saturated part of the wave. We zoom in and see that it is not constant.
Disordered wave when scaling Due to the lack of cyclicality, we are not able to hear any specific frequency in this wave. Therefore, we perceive it as noise.
Deadly sound level
I want to mention a little about the lethal sound level for humans. It originates from 180 dB and higher.
It should be said right away that according to regulatory standards, a safe noise level is considered to be no more than 55 dB (decibel) during the day and 40 dB at night. Even with prolonged exposure to hearing, this level is not harmful.
| Sound volume levels | ||
|---|---|---|
| (dB) | Definition | A source |
| 0 | Not fluffy at all | |
| 5 | Almost inaudible | |
| 10 | Almost inaudible | Quiet rustle of leaves |
| 15 | Barely audible | Rustle of foliage |
| 20 — 25 | Barely audible | Whispers of a man at a distance of 1 meter |
| 30 | Quiet | The ticking of the wall clock ( permissible maximum according to the norms for residential premises at night from 23 to 7 o'clock) |
| 35 | Quite audible | Muffled conversation |
| 40 | Quite audible | Ordinary speech ( the norm for residential premises during the day from 7 to 23 hours) |
| 45 | Quite audible | Talk |
| 50 | Clearly audible | Typewriter |
| 55 | Clearly audible | Talk ( European norm for class A office premises) |
| 60 | (office norm) | |
| 65 | Loud talk (1m) | |
| 70 | Loud conversations (1m) | |
| 75 | Scream and laugh (1m) | |
| 80 | Very noisy | Scream, a motorcycle with a muffler |
| 85 | Very noisy | Loud scream, muffled motorcycle |
| 90 | Very noisy | Loud screams, freight railroad car (7m) |
| 95 | Very noisy | Metro carriage (7 meters outside or inside the carriage) |
| 100 | Extremely noisy | Orchestra, thunder ( according to European standards, this is the maximum permissible sound pressure for headphones) |
| 105 | Extremely noisy | In old planes |
| 110 | Extremely noisy | Helicopter |
| 115 | Extremely noisy | Sandblasting machine (1m) |
| 120-125 | Almost unbearable | Jackhammer |
| 130 | Pain threshold | Airplane at the start |
| 135 — 140 | Contusion | Taking off jet plane |
| 145 | Contusion | Rocket launch |
| 150 — 155 | Contusion, trauma | |
| 160 | Shock, trauma | Shock wave from a supersonic aircraft |
| 165+ | Ruptured eardrums and lungs | |
| 180+ | Death | |
Sound speed in km per hour and meters per second
The speed of sound is the speed at which waves travel through the medium. Below I give a table of the propagation rates in various environments.
The speed of sound in air is much lower than in solid media. And the speed of sound in water is much higher than in air. It is 1430 m / s. As a result, the spread is faster and the audibility is much farther.
Sound power is the energy that is transmitted by a sound wave through the surface of interest per unit of time. Measured in (W). There is an instantaneous value and an average (over a period of time).
Let's continue working with the definitions from the music theory section!
Pitch and note
Height Is a musical term that means almost the same as frequency. The exception is that it has no unit of measurement. Instead of defining sound by the number of cycles per second in the range of 20 - 20,000 Hz, we denote certain frequency values in Latin letters.
Musical instruments produce periodic sound waves of regular shapes, which we call tones or notes.
That is, in other words, it is a kind of snapshot of a periodic sound wave of a certain frequency. The pitch of this note tells us how high or low the note sounds. In this case, lower notes have longer waves. And the tall ones are shorter.
Let's take a look at a 1 kHz sound wave. Now I will zoom in and you will see what the distance between the cycles is.
Sound wave at 1 kHz Now let's take a look at the 500 Hz waveform. Here the frequency is 2 times less and the distance between cycles is greater.
Sound wave at 500 Hz Now let's take a waveform of 80 Hz. Here it will be even wider and much lower.
Sound at 80 Hz We see the relationship between pitch and waveform.
Each musical note is based on one fundamental frequency (pitch). But in addition to tone in music, it also consists of additional resonant frequencies or overtones.
Let me show you another example!
Below is a 440 Hz wave. It is the world's standard for tuning instruments. It corresponds to the note a.
Pure sound wave at 440 Hz We only hear the fundamental tone (pure sound wave). If we zoom in, we will see that it is periodic.
Now let's look at a wave of the same frequency played on the piano.
Periodic piano sound Look, it is also periodic. But it has small additions and nuances. All of these together give us an idea of how a piano sounds. But in addition, overtones also cause the fact that some notes will have a greater affinity for a given note than others.
For example, you can play the same note, but one octave higher. The sound will be completely different. However, it will be akin to the previous note. That is, it is the same note, only played an octave higher.
This kindred relationship between two notes in different octaves is due to the presence of overtones. They are constantly present and determine how closely or distantly certain notes are related to each other.
Power
By the word power in colloquial speech, many mean "power", "strength". Therefore, it is only natural that buyers associate power with loudness: "The more power, the better and louder the speakers will sound." However, this popular belief is fundamentally wrong! By no means always a 100 W speaker will play louder or better than the one with a specified power of “only” 50 W. The power value, rather, speaks not of loudness, but of the mechanical reliability of the acoustics. The same 50 or 100 W is not sound volume at all published by the column. The dynamic heads themselves have low efficiency and convert only 2-3% of the power of the electrical signal supplied to them into sound vibrations (fortunately, the volume of the emitted sound is quite enough to create sound). The value indicated by the manufacturer in the passport of the speaker or the system as a whole only indicates that when the signal of the specified power is applied, the dynamic head or the acoustic system will not fail (due to critical heating and inter-turn short circuit of the wire, "biting" of the coil frame, rupture of the diffuser , damage to flexible suspension systems, etc.).
Thus, the power of an acoustic system is a technical parameter, the value of which is not directly related to the loudness of the acoustics sound, although it is related to it in some way. The nominal values of the power of the dynamic heads, amplifying path, speaker system may be different. Rather, they are indicated for orientation and optimal pairing between components. For example, an amplifier of much lower or much higher power can damage the speaker in the maximum positions of the volume control on both amplifiers: in the first, due to the high level of distortion, in the second, due to the abnormal operation of the speaker.
Power can be measured in a variety of ways and under different test conditions. There are generally accepted standards for these measurements. Let's take a closer look at some of them that are most often used in the characteristics of products of Western companies:
RMS (Rated Maximum Sinusoidal power Is the set maximum sinusoidal power). Power is measured by injecting a 1000 Hz sine wave until a certain level of harmonic distortion is reached. Usually, it is written in the product passport like this: 15 W (RMS). This value says that the speaker system, when a 15 W signal is applied to it, can work for a long time without mechanical damage to the dynamic heads. For multimedia acoustics, higher power values in watts (RMS) compared to hi-fi speakers are obtained as a result of measurements at very high harmonic distortion, often up to 10%. With such distortions, it is almost impossible to listen to sound accompaniment due to strong wheezing and overtones in the dynamic head and the speaker case.
PMPO(Peak Music Power Output). In this case, the power is measured by applying a short-term sine wave with a duration of less than 1 second and a frequency of less than 250 Hz (usually 100 Hz). This does not take into account the level of nonlinear distortion. For example, the speaker power is 500 W (PMPO). This fact says that the speaker system, after reproducing a short-term low-frequency signal, had no mechanical damage to the dynamic heads. Popularly, the units of measurement of power W (PMPO) are called "Chinese watts" due to the fact that the power values with this method of measurement reach thousands of watts! Imagine - powered speakers for a computer consume 10 V * A of electrical power from an AC power supply and at the same time develop a peak musical power of 1500 W (PMPO).
Along with Western standards, there are also Soviet standards for various types of power. They are governed by the current GOST 16122-87 and GOST 23262-88. These standards define such concepts as nominal, maximum noise, maximum sinusoidal, maximum long-term, maximum short-term power. Some of them are indicated in the passport for Soviet (and post-Soviet) equipment. Naturally, these standards are not used in world practice, so we will not dwell on them.
We conclude: the most important in practice is the power value indicated in watts (RMS) with harmonic distortion (THD) values of 1% or less. However, a comparison of products even in this indicator is very approximate and may not have anything to do with reality, because the sound volume is characterized by the sound pressure level. So informativeness of the indicator "power of the acoustic system" - zero.
Sensitivity
Sensitivity is one of the parameters specified by the manufacturer in the characteristics of acoustic systems. The value characterizes the intensity of the sound pressure developed by the speaker at a distance of 1 meter when a signal with a frequency of 1000 Hz and a power of 1 W is applied. The sensitivity is measured in decibels (dB) relative to the hearing threshold (zero sound pressure level is 2 * 10 ^ -5 Pa). Sometimes the designation is used - the level of characteristic sensitivity (SPL, Sound Pressure Level). At the same time, for brevity, in the column with units of measurement, dB / W * m or dB / W ^ 1/2 * m is indicated. It is important to understand, however, that sensitivity is not a linear proportionality factor between sound pressure level, signal strength, and distance to source. Many companies indicate the characteristics of the sensitivity of the dynamic heads, measured under non-standard conditions.
Sensitivity is a more important characteristic when designing your own loudspeaker systems. If you do not fully understand what this parameter means, then when choosing multimedia acoustics for a PC, you can not pay special attention to the sensitivity (fortunately, it is not often indicated).
Frequency response
Frequency response (Frequency response) in the general case is a graph showing the difference in the magnitudes of the amplitudes of the output and input signals over the entire range of reproducible frequencies. The frequency response is measured by applying a sinusoidal signal of constant amplitude when its frequency changes. At the point on the graph where the frequency is 1000 Hz, it is customary to plot the 0 dB level on the vertical axis. The ideal option is in which the frequency response is represented by a straight line, but such characteristics in reality do not exist in acoustic systems. When considering the schedule, you need to pay special attention to the amount of unevenness. The greater the amount of unevenness, the greater the frequency distortion of the timbre in the sound.
Western manufacturers prefer to indicate the range of reproducible frequencies, which is a "squeeze" of information from the frequency response: only cutoff frequencies and unevenness are indicated. Let's say it is written: 50 Hz - 16 kHz (± 3 dB). This means that this speaker system in the range of 50 Hz - 16 kHz, the sound is reliable, and below 50 Hz and above 15 kHz, the unevenness increases sharply, the frequency response has a so-called "blockage" (sharp decline in characteristics).
What is the threat? Reducing the level of low frequencies implies a loss of richness, saturation of the bass sound. The rise in the low-frequency region causes the feeling of booming and humming of the speaker. In the blockages of high frequencies, the sound will be dull, indistinct. Treble rises indicate the presence of annoying, unpleasant hiss and sibilants. In multimedia speakers, the magnitude of the frequency response unevenness is usually higher than that of the so-called Hi-Fi acoustics. All advertising statements of manufacturers about the frequency response of a column of the type 20 - 20,000 Hz (the theoretical limit of the possibility) should be treated with a fair amount of skepticism. At the same time, the unevenness of the frequency response is often not indicated, which can amount to unthinkable values.
Since manufacturers of multimedia acoustics often "forget" to indicate the unevenness of the frequency response of the speaker system, when meeting with a speaker characteristic of 20 Hz - 20,000 Hz, one must keep an eye out. There is a high probability of buying a thing that does not provide even more or less uniform characteristics in the frequency range 100 Hz - 10,000 Hz. It is impossible to compare the range of reproducible frequencies with different unevenness at all.
Harmonic distortion, harmonic distortion
Kg - harmonic distortion factor. A speaker system is a complex electro-acoustic device that has a non-linear amplification characteristic. Therefore, the signal after passing through the entire audio path at the output will necessarily have nonlinear distortions. Harmonic distortion is one of the most obvious and easiest to measure.
The coefficient is a dimensionless quantity. Indicated either as a percentage or in decibels. Conversion formula: [dB] = 20 log ([%] / 100). The higher the harmonic distortion value, the generally worse the sound.
Kg of speakers largely depends on the power of the signal supplied to them. Therefore, it is stupid to draw conclusions in absentia or compare the speakers only by harmonic distortion, without resorting to listening to the equipment. In addition, manufacturers do not indicate the value for the operating positions of the volume control (usually 30..50%).
Electrical impedance, impedance
The electrodynamic head has a certain resistance to direct current, depending on the thickness, length and material of the wire in the coil (this resistance is also called resistive or reactive). When a musical signal is applied, which is an alternating current, the head resistance will change depending on the frequency of the signal.
Impedance(impedans) is the electrical impedance to alternating current measured at 1000 Hz. Typically the speaker impedance is 4, 6, or 8 ohms.
In general, the value of the total electrical resistance (impedance) of the speaker system will not tell the buyer anything related to the sound quality of this or that product. The manufacturer indicates this parameter only so that the resistance is taken into account when connecting the speaker system to the amplifier. If the speaker impedance is lower than the recommended amplifier load, the sound may be distorted or short-circuit protected; if higher, the sound will be much quieter than with the recommended impedance.
Column body, acoustic design
One of the important factors affecting the sound of a speaker system is the acoustic design of the emitting dynamic head (speaker). When designing loudspeakers, the manufacturer usually faces a problem in the choice of acoustic design. There are more than a dozen of them.
Acoustic design is divided into acoustically unloaded and acoustically loaded. The first implies a design in which the oscillation of the diffuser is limited only by the rigidity of the suspension. In the second case, the oscillation of the diffuser is limited, in addition to the rigidity of the suspension, by the elasticity of the air and the acoustic resistance to radiation. Also, the acoustic design is divided into single and double acting systems. A single-acting system is characterized by the excitation of sound coming to the listener through only one side of the diffuser (the radiation from the other side is neutralized by the acoustic design). A double-acting system involves the use of both sides of the cone in shaping the sound.
Since the acoustic design of the speaker practically does not affect the high-frequency and mid-frequency drivers, we will tell you about the most common variants of low-frequency acoustic design of the cabinet.
The acoustic scheme called "closed box" is very widely applicable. Refers to loaded acoustic design. It is a closed case with a speaker diffuser brought out to the front panel. Advantages: good frequency response and impulse response. Disadvantages: low efficiency, the need for a powerful amplifier, high level of harmonic distortion.
But instead of fighting the sound waves caused by vibrations on the back of the cone, they can be used. The most common double-acting system is the bass reflex. It is a pipe of a certain length and section, built into the body. The length and cross-section of the phase inverter are calculated in such a way that at a certain frequency an oscillation of sound waves is created in it, in phase with the oscillations caused by the front side of the diffuser.
For subwoofers, an acoustic scheme with the common name "box-resonator" is widely used. Unlike the previous example, the speaker diffuser is not brought out to the cabinet panel, but is located inside, on the baffle. The speaker itself does not directly participate in the formation of the low-frequency spectrum. Instead, the diffuser only excites low-frequency sound vibrations, which then multiply in volume in the phase inverter pipe, which plays the role of a resonance chamber. The advantage of these design solutions is high efficiency with small dimensions of the subwoofer. Disadvantages are manifested in the deterioration of phase and impulse characteristics, the sound becomes tiresome.
The optimal choice would be medium-sized speakers with a wooden case, made in a closed circuit or with a bass reflex. When choosing a subwoofer, you should pay attention not to its volume (for this parameter, even inexpensive models usually have a sufficient margin), but to faithfully reproduce the entire low frequency range. In terms of sound quality, speakers with a thin cabinet or very small size are most undesirable.
