The physical characteristic of sound loudness is the sound pressure level. Measured in decibels (dB). 30 dB - whisper. 50-65 dB - quiet / loud conversation. 70-80 dB - cry. 100 dB - symphony orchestra tutti. 140 dB - the plane is at the start.
Amplifier power and speaker impedance
Energy characteristic of the electrical signal produced by the amplifier at the output. The unit of measurement is Watt. The level of the output electric power developed by the amplifier depends on the input impedance of the speaker system. 8-ohm speakers are generally quieter than 4-ohm speakers. Have best models amplifiers, the electric power value is doubled when the load impedance is halved. The power of a standard home audio amplifier (into a 4 ohm load) is 25-150 watts. The power of professional amplifiers designed for sounding large spaces (halls, open areas) is hundreds and thousands of watts.
AC power
Usually, the power (peak musical power) of the speakers means the maximum level of the electrical signal, when applied, the acoustics can sound without mechanical damage. The musical power of a loudspeaker is limited by the mechanical and electrical strength of the loudspeakers of the loudspeaker. In some cases, when calculating the power, the allowable level of distortion is also taken into account. There are different standards and methods for measuring speaker power.
Passive speaker specifications often specify the recommended power range for the amplifier connected to the speaker system (for example, 25-120 W). The upper power rating (in this case 120 W) is essentially the music power of this speaker, exceeding which could damage it. The lower value indicates the minimum allowable power of the amplifier (in this case 25 W), together with which this speaker system is still able to provide acceptable quality sounding.
Sensitivity and power
Speaker sensitivity is a characteristic that shows how loud the sound will be when a signal of a certain power is fed to the speaker. Sensitivity is measured in dB / W / m. For example, a sensitivity value of 93 dB / W / m indicates that when 1 W of power is supplied from the amplifier, the speaker creates a sound pressure level of 93 dB at a distance of 1 m on the radiation axis. Typical sensitivity values of modern speakers are in the range 84-97 dB / W / m.
Calculation of the required power
The sound reinforcement power is calculated based on:
1) desired volume level (in dB)
2) technical parameters AS
3) acoustic features of space and speaker placement
The main rule for calculation: a 3 dB gain is equivalent to a twofold increase in input power. An increase of 1 dB corresponds to an increase in power by 1.25 times, and by 2 dB - 1.6 times (since "decibel" is a unit of a logarithmic nature). Accordingly, a 90 dB / W / m speaker at 100 W of power will sound as loud as a speaker with a sensitivity of 87 dB / W / m when connected to 200 W.
For sounding a small room (area 14-16 sq. M) using acoustic systems with a characteristic sensitivity of 90 dB / W / m, it is sufficient to have an amplifier with an output power of 20-30 W per channel. For larger premises of 18-20 sq. m. Optimal results can be achieved with a 40-50 W amplifier. For sounding large spacious halls, a power of hundreds of watts is required. For sounding concert venues - thousands of watts.
The range within which the level of sound pressure developed by the acoustic system is not lower than a certain specified value, in relation to the level averaged over a certain frequency band. The sound pressure level is understood as the ratio of the measured value of the sound pressure modulus to 2 x 10-5 Pa, expressed in decibels. In the recommendations of IEC 581 - 7 minimum requirements to this parameter are 50 - 12500 Hz with a drop of 8 dB in relation to the level averaged over the frequency band 100 - 8000 Hz. A characteristic that largely determines the natural sounding of acoustics. Speaker manufacturers strive to bring the value of this parameter as close as possible to the maximum range perceived by human hearing organs (20 - 20,000 Hz). The effectively reproduced range is determined by the characteristics of the speakers, the design and dimensions of the speaker system, and the parameters of the built-in crossover filter. At low frequencies, the volume of the speaker cabinet plays a decisive role. The larger it is, the more effectively low frequencies are reproduced.
With the reproduction of high frequencies, problems usually arise, modern tweeters (tweeters) even allow ultrasound to be reproduced. Therefore, the range of reproducible frequencies of some speakers exceeds the upper limit of audibility. It is believed that in this case the timbre coloring of the audible components of the sound program is more accurately conveyed. Typical values: 100 - 18000 Hz for bookshelf speakers and 60 - 20,000 Hz for floor speakers. The catalogs provide a graph of the sound pressure developed by the acoustic system, depending on the frequency (graph of the amplitude-frequency characteristic (AFC)), which can be used to determine both the effective operating frequency range and the unevenness of the frequency response, discussed below.
Unevenness of the amplitude-frequency characteristic (unevenness of the sound pressure characteristic)
The degree of non-uniformity of the frequency response is characterized by the ratio of the maximum value of the sound pressure to the minimum, or according to another method, the ratio of the maximum (minimum) value to the average value, in a given frequency range, expressed in decibels. In the recommendations of IEC 581-7, which determine the minimum requirements for Hi-Fi equipment, it is indicated that the frequency response unevenness should not exceed ± 4 dB in the range 100 - 8000 Hz. The best Hi-Fi speaker models have achieved a flatness level of ± 2 dB.
Directional characteristic
Allows to evaluate the spatial distribution of sound vibrations emitted by the acoustic system, and to optimally position the acoustic systems in different rooms. This parameter can be judged by the directional diagram of the speaker, which is the dependence of the sound pressure level on the angle of rotation of the speaker relative to its working axis in polar coordinates, measured at one or several fixed frequencies. Sometimes the drop in the amplitude-frequency characteristic when the speaker is turned by a certain fixed angle is displayed on the main graph, in the form of additional branches of the frequency response.
Characteristic sensitivity (Sensitivity, Efficiency)
The ratio of the average sound pressure developed by the acoustic system in a given frequency range (usually 100 - 8000 Hz) on the working axis, reduced to a distance of 1 m and an input electrical power of 1 W. In most Hi-Fi speaker models, the characteristic sensitivity level is 86 - 90 dB (in technical literature, dB / m / W is often indicated instead of dB). In recent years, high-quality broadband speakers with a high sensitivity of 93 - 95 dB / m / W and more have appeared. A parameter that determines what dynamic range, that is, the ratio of the maximum sound pressure to the minimum, expressed in decibels, the speaker can provide. The wide dynamic range makes it possible to reproduce complex musical compositions with great fidelity, especially jazz, symphonic, chamber music.
Distortion, Total Harmonic, THD
It characterizes the appearance in the process of transformation of spectral components that were absent in the original signal, distorting its structure, that is, ultimately, the fidelity of reproduction. An important parameter, since the "contribution" of the speaker to the total coefficient of nonlinear distortion of the entire sound path is usually the maximum. For example, the total harmonic distortion modern amplifier is hundredths of a percent, while the typical value of this parameter for acoustics is a few percent. As the signal power increases, the THD increases.
Electric (acoustic) power (Power Handling)
Power determines the sound pressure level and dynamic range (taking into account the characteristic sensitivity) that a speaker can potentially provide in a given room. Several capacity types defined by different standards are used:
Characteristic
At which the speaker provides a given level of average sound pressure. In the IEC recommendations, the value of this level is set to 94 dB at a distance of 1 meter.
Maximum (limiting) noise or passport (Power Handling Capacity)
In which the speaker system can work for a long time without mechanical and thermal damage when tested by special noise signal, similar in spectrum to real music programs (pink noise). According to the measurement technique, it coincides with the rated power, determined in domestic standards.
Maximum Sinusoidal Testing Power, Rated Maximum Sinusoidal Power
The power of a continuous sinusoidal signal in a given frequency range, at which the speaker can operate for a long time without mechanical and thermal damage.
Long Term Maximum Input Power
The power that the acoustics can withstand without mechanical or thermal damage for one minute, with the same test signal as for the rated power. The tests are repeated 10 times with an interval of 1 minute.
Short Term Maximum Input Power
The power that the speaker withstands when tested with a noise signal with the same distribution as for the rated power for 1 second. The tests are repeated 60 times with an interval of 1 minute.
Peak Music Power Output (PMPO)
A favorite parameter of manufacturers who are concerned with selling their own, often not very high-quality, equipment. The measurement technique, defined by the German DIN 45500 standard, is as follows: a short-term (less than 2 seconds) signal with a frequency of less than 250 Hz is applied to the speaker. The acoustics are considered to have passed the test if there are no noticeable (!) Distortions. This technique allows the above-mentioned manufacturers to supply their products with bright stickers with the following text: "P.M.P.O. ..." (or "Musical Power ...") "... 100!", "... 200!" and even ... "... 1000 Wt!" It is clear that this parameter weakly characterizes the real quality of sound reproduction.
When choosing a pair of amplifier plus speakers, it is desirable that the actual maximum power of the speaker system exceeds the power of the amplifier by about 30 percent or more. In this case, you will be insured against failure of the acoustics, due to the supply of a signal to it of an unacceptably high level. For example, with an amplifier with a power of 50 W per channel, you can use speakers with a rated power of 75 W each. How much amplifier power is sufficient for high-quality sound reproduction? This is largely determined by the parameters of the room, the characteristics of the acoustic systems, and the needs of the listener himself. With a high degree of approximation, it is believed that for modern medium-sized living spaces, the power of the amplifier should be at least 20 watts.
Electrical (input) resistance (impedance)
The most common values are 4, 8, or 16 ohms. This parameter is important when choosing an amplifier with which the speaker will work. It is optimal to use a speaker system with an impedance corresponding to that specified in the amplifier's passport. Such a solution will ensure the perfect match between the characteristics of the acoustics and the amplifier, that is, the maximum sound quality.
Earlier in the specifications for loudspeakers manufacturers usually indicated two values of power: nominal, i.e. power value at which harmonic distortions are normalized, and musical, which was the maximum possible power sound signal at the input of the speaker system, which it could withstand without its mechanical damage. The value of the musical power of the loudspeaker is limited by the mechanical and electrical strength of the loudspeakers of the loudspeaker system.
Recently, the specifications began to indicate the range of recommended power of a low-frequency amplifier connected to the AC, for example: 25-120 W. The upper power rating, in this case 120 W, is essentially the music power of this speaker, exceeding which could damage it. Well, the lower value indicates the minimum allowable power of the low-frequency amplifier (in this case, 25 W), together with which this speaker system is still capable of providing high sound quality.
Needless to say, this is very convenient and informative, as it determines the requirement for a low-frequency amplifier operating with this speaker not only "from above", but also "from below", taking into account the values of the characteristic sensitivity of this speaker system.
It should also be noted that the level of the electric power developed by the low frequency amplifier at its output largely depends on the input impedance of the speaker system. 8-ohm loudspeakers tend to sound quieter than 4-ohm ones, since the amplifier must provide twice the output voltage in the case of 8-ohm acoustics to provide equal electrical power. Most low frequency amplifiers have a higher output power into a 4 ohm load than an 8 ohm load.
At the same time, the high impedance of 8-speaker speakers provides twice the value of their damping coefficient (damping factor) by the low output impedance of the amplifier, so in general they sound more clearly on bass than 4-ohm speakers. This largely explains the different nature of the sound of the same speaker system with different types amplifiers. Judge for yourself, if one of the amplifiers has an extremely low output impedance (high damping factor), this amplifier will damp the loudspeaker much better than an amplifier with a relatively high output impedance.
In general, the sound of the speaker system in a duet with the first amplifier will be clearer than in the second case. Further, low-frequency amplifiers differ significantly from each other in their ability to deliver large current values to the load. Good amplifiers audio frequency are almost ideal sources of current and therefore are able to "hold tightly" even acoustic systems with a complex character of changing their input impedance. An indirect test for the "correctness" of an audio frequency amplifier is the nature of the change in its dynamic power when the load changes from 8 to 2 (or even 1) Ohm, given in the specifications for the amplifier.
The best amplifier models double the electrical power when the load impedance is halved. The same amplifier models whose output power "sags" with decreasing load, most likely, will not provide good quality sound paired with "capricious" speaker systems, the input impedance of which changes significantly in the audio frequency band.
But many types of loudspeakers with a nominal input impedance of, say, 8 ohms, can have an impedance of 4 or even 3 ohms at some frequencies! Here is one of the answers to the question why the same speakers sound differently in different audio systems.
The speaker system is an integral part of any audio system, from cinema and concert equipment to home theater or conventional computer multimedia system. The speaker system includes several sound (acoustic) speakers (AC), their number and purpose can vary greatly.
To effectively sound a small room, sometimes two solid speakers are enough to enjoy all the nuances of the sound picture of modern films or the most advanced computer games you will need a multichannel active speaker system.
What exactly do you need to know to purchase acoustics of the required price level and sound quality? Read about this and the features of operation below.
Acoustic systems | History of multichannel sound reproduction
Historically, the first multichannel sound reproduction system was stereophony... Two audio speakers located in front of the listener provide the spatial distribution of the sound sources of the audio track being listened to. Naturally, in this case, the sound recording should be performed in stereo format and listened to through a two-channel amplifier with a right and left channel (PK and LK).
According to the modern classification, such acoustics are designated - 2.0, which means two front side speakers in the absence of a subwoofer. The modern version of the stereo system is 2.1 format. In this case, a subwoofer is added to the two front speakers, designed exclusively for reproducing low-frequency sounds.
The fact is that to achieve high-quality sound output from the front speakers according to low frequencies(LF) is a rather difficult task, while the acoustics are significantly increased in size and price. It is much easier and cheaper to make a separate woofer - a subwoofer. The signal for the subwoofer is separated from the left and right channel signals. This practically does not affect the quality of the stereo effect, since the human ear almost does not perceive the location of the source of low-frequency sounds. The main information about the localization of sound sources is in the mid-frequency (MF) and high-frequency (HF) parts of the range, for which the two front speakers are responsible.
A further improvement in audio systems was four-channel sound reproduction. An analog version of such systems was called quadrophony... In this case, two rear speakers are added to the two front speakers. The 4.1 system also includes a subwoofer to simplify the front speakers. However, quadrophony was not widely spread. It did not give a significant increase in sound quality and the effect of volume, but it required very expensive analog equipment for recording and reproducing sound phonograms. However, the digital version of the 4.1 system has been successfully used in some computer games.
Acoustic systems | Multichannel audio and Dolby technologies
The specialists of the American company made a significant contribution to the subsequent improvement of multichannel sound systems. Dolby Laboratories, who developed digital coding algorithms at the end of the last century, allowing to receive sound at the level of a cinema and concert hall at home. Format Dolby Digital, often used for scoring films, especially on DVDs. It provides three-dimensional acoustic scenes, clearer detail, natural movement of sound sources, stereo sound in the back space.
Today the most advanced active acoustics are equipped with digital decoders Dolby Theater System(DTS) and Dolby Pro Logic(DPL) is an analog surround sound system used on HI-Fi VHS videotapes and broadcast television.
The minimum audio system required for a home theater must comply with the 5.1 format. In this system, in addition to the subwoofer, there are five so-called. satellites (smaller speakers). Two front speakers, a center one and a subwoofer, are placed in front of the listeners and reproduce the main sound picture. The two rear speakers play a less important role. On them lies the "sound" in musical compositions, the creation of three-dimensional effects in games.
Advanced system Dolby Digital EX allows, due to the introduction of additional rear surround channels (acoustics 6.1, 7.1), to obtain an even higher degree of localization in the space of sound sources.
For full reproduction of multichannel recordings of Dolby Digital and Dolby Pro Logic formats using only two speakers, a processing algorithm is used Dolby Virtual Speaker.
Acoustic systems | Specifications
Objectively, the quality of a speaker system can be judged by a set of characteristics. To the main parameters sound speakers and the loudspeakers used in them include:
- range of reproducible frequencies;
- amplitude-frequency characteristic (AFC);
- power;
- sound pressure level;
- sensitivity;
- dynamic range;
Speaker frequency range
The wider frequency range, the better the audio system can sound. True, with an insignificant difference in this characteristic between the two speaker systems, not every ear will be able to pick it up. And, in general, the maximum necessary is considered to be a reproducible frequency band of 20 ... 20,000 Hz. However, for many, lowering the upper limit to 16 kHz may be quite sufficient. As for the lower threshold of reproducible frequencies (especially revered by many music lovers), then for medium price range 30-40 Hz is quite an acceptable border, provided there is a high-quality frequency response.
Frequency response (AFC) of the speaker system
Frequency response- graphical dependence of the output signal level (voltage, power or sound pressure) on frequency. Ideally, the frequency response should be a straight horizontal line. Alas, the real frequency response has many peaks and dips, demonstrating an overestimated and underestimated level of sound reproduction at certain frequencies and really characterizes the sound quality of an acoustic column or speaker. The quality of the frequency response is assessed by the unevenness of the curve, in decibels. Unfortunately, many manufacturers do not provide this schedule in technical description acoustics.
Speaker power
It is by this parameter that many people choose acoustics for themselves, since they consider it to be the equivalent of loudness. However, this is not entirely true for acoustics. The power of a speaker or loudspeaker is measured in watts (W) and determines the maximum possible power of an electrical signal applied to it. If the rating value for this acoustics is exceeded, the level of distortion increases sharply, and if it is exceeded, the speaker may fail due to damage to the coil winding.
Acoustics manufacturers, knowing that for many listeners this is the main characteristic, they are often cunning, passing on wishful thinking. The fact is that there are different types, methods and units for measuring the power of acoustic systems. For example, some manufacturers indicate the so-called peak short-term power (PMPO), while others indicate the average electrical power (RMS), and there is also music power. All this leads to a rather significant difference in numbers with approximately the same real power.
Sound pressure level of the speaker
It is this parameter that determines the possible loudness level from your acoustics, measured in dB with respect to the zero level corresponding to the hearing threshold of a person in silence at a sound frequency of 1 kHz. The zero level is assumed to be a pressure of 20 μPa.
Sound pressure in acoustics is the difference between the instantaneous pressure value at the measuring point caused by the sound wave and normal atmospheric pressure in the absence of sound. Pressure is often measured in pascals (Pa).
Speaker sensitivity
This parameter of the acoustic system determines the efficiency of converting electrical energy into sound and is one of the most important. Loudspeakers with less power, but with higher sensitivity can often produce louder sound.
Sensitivity is usually characterized by the level of sound pressure (in decibels), measured at a certain distance from the audio speaker when an electrical signal with a power of 1 W is applied to its input. It is necessary, however, to take into account that the measurement conditions (distance, power input) may differ for different manufacturers of acoustics.
Speaker dynamic range
Dynamic range the acoustic system determines the possibilities of reliable reproduction of sound phonograms with a significantly varying volume level. The greatest dynamic range is required for the reproduction of classical music, where the rumble of timpani and muffled singing of a flute can coexist.
Numerically, the parameter is measured in decibels and is determined by the ratio between the loudest and quietest sounds. The wider the dynamic range, the richer the acoustic capabilities of the audio system.
Speaker impedance
Or resistance - the total electrical resistance of acoustics. For loudspeakers and speakers, typically 4, 6, 8, or 16 ohms. In general, impedance is not directly related to the sound quality of a particular speaker system. However, it is this parameter that must be taken into account when connecting a speaker system to an amplifier. If the impedance value of the speaker is lower than the output impedance of the amplifier, there will be some (slight by ear) distortion in the sound, but if the volume is too high, such a connection may damage the amplifier; if the impedance of the acoustics is higher than the output impedance of the amplifier, then the sound will be much quieter.
For active speaker systems, important parameters are harmonic distortion caused by non-linear distortion of the amplifier and the ratio between the level of the useful signal and the level of the amplifier introduced "noise" signal.
Speaker Harmonic Distortion (THD)
At the same time, it should be noted that nonlinear distortions are very noticeable only for transistor amplifiers... Tube systems, having much higher harmonic coefficients, subjectively have a very high sound fidelity, for which they are appreciated by music lovers.
Signal-to-noise ratio of the speaker system
All of the above parameters greatly simplify the selection of the required acoustics. Unfortunately, manufacturers do not always allow an objective assessment of the quality of their products, applying a minimum set of parameters with a maximum of advertising statements. At the same time, when buying, do not forget about the individual characteristics of sound perception, and thoroughly listen and compare several types of acoustics.
Knowing the basic characteristics of speakers is much easier select the necessary sound equipment or form a sound package of excellent quality.
To one of the main parameters by which they characterize acoustic systems can be attributed to the effective operating frequency range. This range is considered to be the frequency range within which the sound pressure level is not lower than a given unit.
An extremely important characteristic for loudspeaker systems is the unevenness of the frequency response or frequency response. This parameter specifies the degree of flatness in amplitude during playback of the audio signal. The ideal frequency response is considered a straight line, but in reality this characteristic can have a large number of dips and peaks, which can be justified by the not ideal state of the other components of the system. Unevenness of the frequency response is usually characterized by the ratio of the values of the maximum and minimum sound pressure and is expressed in decibels (dB).
