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Choosing acoustics for PC.

Choosing acoustics for PC.

For many users, choosing active speaker systems for a computer is a very difficult task. And this is not surprising, because there are hundreds of similar speaker models on the market, and information can now be gleaned from numerous sources & # x97; from articles in the online and offline press, from manufacturers’ websites on the web. True, sometimes there is only a meager description and a list of technical characteristics that are almost the same for all models. The user has no choice but to choose the acoustics that suits him. We will try to help you with this by explaining what you need to pay attention to in the first place, and what to treat with a grain of salt.

We will also try to figure out & # x97; what kind of sound can you hear from speakers of this or that class.

Classification of PC acoustics by purpose.

For decorating a computer desk (the reasons may be different) and signaling notifications about operating system events (such as a welcome gurgle when the computer boots up and sounding the arrival of new messages from an ICQ pager). In this case, the appearance and design of the speaker case has the highest priority..

Criteria for choosing PC acoustics.

The most common approach when choosing acoustics is some kind of limited amount of money allocated for the purchase. Very often, readers write us letters or create topics in our Multimedia conference: “Which 2.1-set to choose in the category up to $ 100” or “Recommend speakers in the range of $ 20- $ 50”. In this case, you need to remember that for such small amounts, a compromise is inevitable between price, quality and manufacturer’s popularity.

You also need to understand that all multimedia speaker sets will never replace even the youngest models of household wooden Hi-Fi acoustics..

As you can see, everything is not as straightforward as it seems at first glance. If you plunge even deeper and begin to analyze the currently available assortment of goods and the capabilities / needs of a particular buyer, then each will have their own best buy. So to advise specific models & # x97; extremely difficult.

However, we can warn the reader against at least elementary mistakes when choosing acoustics..

Least of all it is worth paying attention to colorful advertising inscriptions on packaging boxes, which attract the attention of only naive and uneducated users. Also, do not take seriously the characteristics indicated on the boxes in large letters, since they are usually pure advertising that has no connection with reality (for example, 2500 watts of power for speakers the size of a 0.33 can of Pepsi). Pay special attention to the material of which the case is made.

Advantages of speakers with plastic enclosures: small size, ergonomics, a wide range of engineering and design shapes and colors, low price. Disadvantages: small size does not allow reaching low frequencies, rattling at medium and high volumes, mid-frequency resonances in sound.

We want to immediately warn you against hasty conclusions when comparing acoustics according to the technical characteristics given on the manufacturer’s website or in the product passport. It should be borne in mind that the marketing department will never miss the opportunity to “outwit” the buyer and indicate the most profitable data. Whatever numbers you see, do not flatter yourself and treat them with skepticism.

For example, on some speakers they write: “power 100 W, distortion 0.01%.” All this is great, but the problem is that power and distortion were measured separately. Power & # x97; at 10%, and distortion & # x97; at 1 W. At the same time, probably such “strange” measurement conditions are described somewhere in the corner in small letters, so that during a possible investigation the user has no grounds for claims.

We also always advise you to be sure to listen before buying how your chosen speakers sound. If possible, immediately compare the sound quality with some alternative solution. Moreover, the smaller the time gap between these auditory tests, the more believable and correct your conclusions will be. It is absolutely impossible to take into account any memorable sensations from listening to the acoustic system (like “I listened to my neighbor last week”).

They are not suitable because the perception of sound depends on the psychophysical state of the individual at the moment, plus, the auditory sensations of a person (especially from habit) are very fuzzy and quickly erased from memory.

Now about speaker systems that include several speakers. As you know, among the multicolumn configurations, there are mainly 4.1, 5.1, 6.1 systems. Outwardly, they differ a little: 5.1 acoustics, unlike 4.1, have one more speaker in the kit (the so-called “center”). But in fact, the difference is not only that.

It all depends on which



sound card is installed in your computer..

If you use a four-channel sound card with a 5.1-set of acoustics, then the center and subwoofer will most likely not play. If you use a six-channel card with a 4.1-set of acoustics, then you will never feel the full-fledged six-channel Dolby Digital and DTS formats, whatever the speaker manufacturer would write about their super-duper “virtual center channel” technology. The reason lies in the absence of separate inputs for the center and subwoofer on 4.1 systems (although the four-channel mode of operation, like the stereo mode, for such cards necessarily exists and can be easily selected in the settings).

Detailed decoding of some characteristics of acoustics.

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! It is far from always that 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 & # x97; it is not at all the volume of the sound emitted by the speaker. 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 accompaniment). 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 acoustic system will not fail (due to critical heating and interturn short circuit of the wire, “biting” of the coil frame, rupture of the diffuser , damage to the flexible hangers of the system, etc.).

Thus, the power of the speaker system & # x97; this is a technical parameter, the value of which is not directly related to the loudness of acoustics sounding, 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. They are indicated rather 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: on the first & # x97; due to the high level of distortion, the second & # x97; due to the abnormal operation of the column.

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 (Root Mean Squared & # x97; root mean square value). Power is measured by injecting a 1000 Hz sine wave until a certain level of harmonic distortion is reached. Usually in the product passport it is written like this: 15 W (RMS). This value indicates 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 the soundtrack due to strong wheezing and overtones in the dynamic head and the speaker case.

PMPO (Peak Music Power Output & # x97; Peak Music Power). In this case, the power is measured by applying a short-term sinusoidal signal 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 suggests 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 & # x97; Powered PC speakers draw 10 V * A from AC power while delivering 1500 W peak musical power (PMPO).

Along with Western standards, there are also Soviet standards for various types of power. They are regulated by GOST 16122-87 and GOST 23262-88, which are still valid. These standards define concepts such 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 have nothing to do with reality, because the sound volume is characterized by the sound pressure level. Therefore, the informativeness of the indicator “speaker power” & # x97; zero .

Sensitivity.

Sensitivity & # x97; one of the parameters specified by the manufacturer in the characteristics of loudspeakers. The value characterizes the intensity of the sound pressure developed by the speaker at a distance of 1 meter when a signal is supplied with a frequency of 1000 Hz and a power of 1 W. The sensitivity is measured in decibels (dB) relative to the hearing threshold (zero sound pressure level is 2 * 10 ^ -5 Pa). Sometimes the notation is the characteristic sensitivity level (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 coefficient of proportionality 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 & # x97; a characteristic that is more important when designing your own speaker 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).

AFC (Frequency Responce)

The amplitude-frequency characteristic (AFC) in the general case is a graph showing the difference in the magnitudes of the amplitudes of the output and input signals in the entire range of reproducible frequencies. The frequency response is measured by applying an electric sinusoidal signal of constant amplitude when its frequency changes. Moreover, 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 variant is in which the frequency response is represented by a straight line, but such characteristics in reality are simply not available for acoustic systems.

When considering the schedule, you need to pay special attention to the amount of unevenness. The greater the amount of unevenness, the more frequency distortion of the timbre in the sound..

Western manufacturers prefer the term FR (frequency response) & # x97; 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 frequency response (± 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 20-20000 Hz (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 irregularities at all.

Harmonic Distortion (THD)

The abbreviation THD literally stands for Total Harmonic Distortion, but it means a very definite term & # x97; harmonic distortion. 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..

Harmonic distortion results from the addition of unnecessary harmonics to the original signal due to the non-linearity of the input / output characteristic. These parasitic harmonics give the sound a new timbre and lead to irreparable losses in the sound. Harmonic distortion is measured by applying a sine wave at 1000 Hz. With the help of a special filter, excess harmonics are found in the audio signal and their power is determined.

In Soviet standards, along with the harmonic coefficient, the coefficient of nonlinear distortion is also measured, which is closer to the term THD + N. In general, these coefficients do not coincide. Total Harmonic Distortion is measured in either percentage or decibels: [dB] = 20 log ([%] / 100). The higher the THD or THD + N value, the worse the sound usually becomes. There is a popular belief among audiophiles that certain distortions that make the sound “soft” and “warm” can be pleasant to the ear.

However, this does not apply to computer acoustics and transistor amplifiers from the “consumer goods” category..

The THD of the speakers depends a lot on the power of the signal supplied to them. Therefore, it is foolish to draw conclusions in absentia or compare the speakers only by THD, without resorting to listening to equipment (although even the most authoritative publications sometimes follow this easy path). In addition, for the operating positions of the volume control (usually 30 …

50%), the THD value is not indicated by manufacturers.

Electrical resistance, impedance (impedans)

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 supplied, which is an alternating current, the head resistance will change depending on the frequency of the signal..

Impedance (impedans) & # x97; it is the electrical impedance to alternating current measured at 1000 Hz. Typically speaker impedans are 4, 6 or 8 ohms.

In general, the value of the impedans 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 impedance value of the speaker is lower than that of the amplifier, non-linear distortion will be present in the sound; if higher, then the sound will be much quieter than with equal resistance.

Column body, acoustic design.

Acoustic design is one of the important factors affecting the sound of a speaker system. When designing loudspeakers, the manufacturer usually faces a problem in the choice of acoustic design. There are more than a dozen types 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 vibration 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). The 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 options for low-frequency acoustic design of the cabinet in multimedia.

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, 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 optimal choice would be medium-sized speakers, if possible 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 (according to this parameter, even computer subwoofers usually have a sufficient margin), but to faithfully reproduce the entire low frequency range. In terms of sound quality, the most undesirable speakers are those with drilled holes for ventilation, thin plastic or very small dimensions, barely larger than the speaker..

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