About speaker performance parameters

1. Power

The power determines the loudest sound that the speaker can emit, and it feels like how powerful the sound of the speaker can be. According to international standards, there are two marking methods for power:

(1) Rated power (RMS: sine wave root mean square): refers to driving an 8Ω loudspeaker within the rated range. The continuous analog signal of the waveform is specified. After a certain interval and repeating a certain number of times, the speaker does not cause any damage. High power

(2). Instantaneous peak power (PMPO power): refers to the maximum power that the speaker can withstand in a short time.

The United States Federal Trade Commission stipulated the power calibration standard in 1974: The effective wattage measured when the harmonic distortion is less than 1% in the range of 20 to 20000 Hz is the effective wattage measured when an 8Ω speaker load is driven by two channels. For output power, the marked power is the rated output power.

The power of the speaker is mainly determined by the power of the power amplifier chip and the power of the power transformer. For an ordinary home user's room of about 20 square meters, 60W power in the sense (referring to the effective output power of the speaker 30W×2) is enough, but the larger the reserve power of the power amplifier, the better, which is 2 times the actual output power the above. For example, if the speaker output is 30W, the power amplifier capacity is greater than 60W.

2. Frequency range and frequency response

(1) Frequency range: refers to the range between the low effective playback frequency and the high effective playback frequency that the audio system can reproduce;

(2) Frequency response: When connecting an audio signal output with a constant voltage to the system, the sound pressure generated by the speaker increases or attenuates with the change of frequency, and the phase changes with the frequency. This The relative change (variation) between sound pressure and phase and frequency is called frequency response, in decibels (Db).

The frequency characteristic of the sound system is usually described by the frequency response curve with the ordinate of the decibel scale representing the power and the abscissa of the logarithmic scale representing the frequency.

The high-frequency cut-off point and low-frequency cut-off point of the frequency response: When the sound power is 3dB lower than the normal power, this power point is called the high-frequency cut-off point and the low-frequency cut-off point of the frequency response. The frequency between the high-frequency cut-off point and the low-frequency cut-off point is the frequency response of the device; the curves of sound pressure and phase lag with frequency are called "amplitude-frequency characteristics" and "phase-frequency characteristics", collectively called "frequency" characteristic". The smaller the decibel value, the flatter the frequency response curve of the speaker, the smaller the distortion, and the higher the performance. For example, the frequency response of a speaker is 60Hz～18kHz +/- 3dB. These two concepts are sometimes indistinguishable and are called frequency response.

In theory, a frequency response of 20 to 20000 Hz is sufficient. The sound below 20Hz can not be heard, but other human sensory organs can detect it, that is, the so-called bass power can be felt. Therefore, in order to play various musical instruments and language signals well, the amplifier must achieve the goal of high fidelity. In order to reproduce all the harmonics of the tone.

4. Loudness

　　The strength of the sound is called the intensity, which is determined by the amplitude (sound pressure) of the rapid changes in air pressure. However, the human ear’s subjective perception of intensity is not consistent with the objective actual intensity. People call the subjective perception of strength as loudness, and its measurement unit is also decibels (Db), which is based on the sound of 1000 Hz sound at different intensities. The pressure ratio is determined by l/10 of its common logarithmic value. The reason for taking the logarithm is because the increase in intensity and loudness is not proportional, but the relationship between the true number and the logarithm! For example, when the sound intensity is 10 times higher, it sounds only one level (10dB), and when the intensity is 100 times higher, it sounds two levels (20dB). For a 1000Hz sound signal, the low sound pressure that the human ear can feel is 2×10E-5Pa, and this sound pressure level is set as 0dB. When the sound pressure exceeds 130dB, the human ear will not be able to tolerate it, so the dynamic range of human ear hearing is 0～130dB.

People have different perceptions of sounds with equal intensity and different frequencies; the higher the sound pressure level, the flatter the human auditory frequency characteristics; the lower the sound pressure level, the smaller the human auditory frequency range; the frequency f<16-20Hz and f ＞18～20KHz sound, no matter how high the sound level is, the human ear can't hear it. Therefore, the hearing frequency of the human ear is 20Hz～20KHz, this frequency band is called audio frequency or audio frequency; regardless of the sound pressure level, the human ear is sensitive to the sound of 3KHz～5KHz frequency. Most people can't feel the sudden change of the signal sound level below 3dB, so 3dB is often used as the allowable frequency response curve variation range for the audio system.

5. Distortion

　　 is divided into harmonic distortion, intermodulation distortion and transient distortion. Harmonic distortion refers to the distortion caused by the addition of high-order harmonic components that the original signal does not have in the sound playback; intermodulation distortion mainly affects the tone of the sound; transient distortion is because the speaker has a certain inertial quality. The vibration of the basin body cannot keep up with the difference between the original signal and the playback tone caused by the instantaneous vibration of the electrical signal. It is more important in speakers and speaker systems. It directly affects the degree of sound quality and tone reproduction. This item is often expressed as a percentage. The smaller the value, the smaller the distortion. The distortion of ordinary multimedia speakers should be less than 0.5%, and the distortion of the subwoofer is generally larger, less than 5% is acceptable.

6. The sensitivity of the speaker (unit Db)

　For every 3dB difference in the sensitivity of the speaker, the output sound pressure will double. Generally, 87 Db is the medium sensitivity, 84 Db or less is low sensitivity, and 90 Db or more is high sensitivity. The increase in sensitivity comes at the expense of increased distortion, so as a high-fidelity speaker, to ensure the degree of sound reproduction and reproducibility, some requirements for sensitivity are reduced. But it cannot be said in reverse that the sound quality of high-sensitivity speakers must be poor and low-sensitivity speakers must be good. It is difficult to drive low-sensitivity speaker amplifiers (requiring a larger reserve power of the amplifier). So although sensitivity is an indicator of speakers, it has nothing to do with the sound quality of speakers.

7. Impedance

It refers to the ratio of the voltage to the current of the speaker input signal. The input impedance of a speaker is generally divided into high impedance and low impedance. The impedance higher than 16Ω is high impedance, and the impedance lower than 8Ω is low impedance. The standard impedance of the speaker is 8Ω.

When the power amplifier is the same as the output power, a low-impedance speaker can obtain a larger output power, but if the impedance is too low, it will cause under-damping and bass degradation. Therefore, although this indicator has nothing to do with the performance of the speakers, do not buy low-impedance speakers. The recommended value is the standard 8Ω. The impedance of headphones is generally high impedance-32Ω is very common. The impedance of a power amplifier can generally be marked as equivalent impedance, such as an output of 130W under 4Ω, which is roughly equivalent to an output of 80W of equivalent value. There is a term that is easy to confuse with it called "damping coefficient", which refers to the speaker impedance divided by the internal resistance of the amplifier source, ranging from about 25 to 1000. The speaker cone has to oscillate several times after the electrical signal has disappeared to completely stop swinging, and the current and magnetic field generated by the voltage from the coil can prevent this parasitic movement, which is damping. The magnitude of the current, that is, the effect of damping, depends on the internal resistance of the current flowing through the amplifier output stage. This resistance is much lower than the rated impedance of the speaker. The typical value is 0.1Ω, but due to the series resistance and crossover of the speaker voice coil The existence of the series resistance of the network makes it difficult to achieve a damping coefficient of 50.

8. Signal-to-noise ratio

　　 refers to the ratio of the normal sound signal played back by the speaker to the noise signal (power) when there is no signal. Also denoted by Db. For example, the signal-to-noise ratio of a tape recorder is 50dB, that is, the output signal power is 50dB greater than the noise power. The higher the signal-to-noise ratio, the lower the noise. The International Electrotechnical Commission's requirements for the signal-to-noise ratio are that the preamplifier is greater than or equal to 63dB, the post-amplifier is greater than or equal to 86dB, and the combined amplifier is greater than or equal to 63dB. The appropriate value of the combined amplifier's signal-to-noise ratio should be greater than 90dB; radio head: 50dB for FM stereo, in fact it is better to reach 70dB or more; 56dB for tape recorder (normal band), but the signal-to-noise ratio after Dolby noise reduction Great improvement. For example, the signal-to-noise ratio after noise reduction by Dolby B can reach 65dB, and the signal-to-noise ratio after noise reduction by Dolby C can reach 72dB (all refer to ordinary belts); the signal-to-noise ratio of CD players can reach more than 90dB, noble It can reach more than l10dB. When the signal-to-noise ratio is low, the noise is serious when the small signal is input, and the sound of the entire range is obviously turbid, so it is not recommended to buy speakers with a signal-to-noise ratio of less than 80dB! The 70 Db subwoofer is not recommended for the same reason.

9. Scalability

This refers to whether the speaker supports multi-channel simultaneous input, whether there is an output interface for passive surround speakers, whether there is a USB input function, etc. The number of external surround speakers that a subwoofer can connect to is also one of the criteria for measuring expansion performance.

10. Sound technology

Hardware 3D sound effect technologies are now more common, including SRS, APX, Spatializer 3D, Q-SOUND, Virtaul Dolby, and Ymersion. Although they implement different methods, they can all make people feel obvious three-dimensional sound field effects. The first three are more common. They are all applied to the Extended Stereo theory, which is the additional processing of the sound signal through the circuit, so that the listener feels that the sound and image orientation is extended to the outside of the two speakers, so as to expand the sound and image, so that people have space. Sense and three-dimensional sense, produce a wider stereo effect. In addition, there are two sound enhancement technologies: active electromechanical servo technology (essentially using the principle of Helmholtz resonance), BBE high-definition plateau sound reproduction system technology and "phase fax" technology, which also have a certain effect on improving sound quality. For multimedia speakers, the SRS and BBE technologies are relatively easy to achieve and have good results, which can effectively improve the performance of the speakers.

11. Pitch

　　 refers to a signal with a specific and usually stable pitch. In layman's terms, it is the degree to which the sound is pitched. It mainly depends on the frequency, and it is also related to the sound intensity. The human ear responds to high-frequency sounds as high-pitched sounds, and the human ear responds to low-pitched sounds with low-frequency sounds. The change in pitch with frequency (Hz) is basically logarithmic. Different musical instruments play notes of the same frequency, although their timbre is different, but their pitch is the same, that is, the fundamental frequency of the playing sound is the same.

12. Tone

　　 The perception of sound quality is also the characteristic quality that distinguishes one kind of sound from another. When different musical instruments play the same tone, their colors can be different. This is because although their fundamental frequencies are the same, the harmonic components are quite different. Therefore, the timbre not only depends on the fundamental frequency, but also is closely related to the harmonics that are integral multiples of the fundamental frequency. This makes each instrument and each person have a different timbre.

13. Stereo separation

　　 refers to the ability and degree of non-interfering signals between two channels, that is, the degree of isolation, which is usually expressed by the difference between the signal level in one channel and the level that leaks to the other channel. If the stereo separation is poor, the stereo perception will be weakened. The low index of stereo separation specified by the International Electrotechnical Commission is greater than or equal to 40dB at 1KHz, and it is actually better to reach 60dB; the stereo separation of FM stereo broadcasting specified by the European Broadcasting Union is> 25dB, which can actually achieve more than 40dB . Stereo channel balance refers to the difference in the gain of the left and right channels, and is generally represented by the largest difference between the output levels of the left and right channels. If the imbalance is too large, the stereo sound image position will deviate, and this index should be less than 1dB.

14. Damping coefficient

　　 refers to the ratio of the rated load (speaker) impedance of the amplifier to the actual impedance of the power amplifier. A large damping coefficient indicates that the output resistance of the power amplifier is small. The damping coefficient is the ability of the amplifier to control the movement of the speaker cone after the signal disappears. An amplifier with a high damping coefficient is more like a short circuit to the speaker, reducing its vibration when the signal is terminated. The output impedance of the power amplifier will directly affect the low frequency Q value of the speaker system, thereby affecting the low frequency characteristics of the system. The Q value of the loudspeaker system should not be too high. Generally, it is better in the range of 0.5～l. The output impedance of the power amplifier is the factor that increases the low frequency Q value. Therefore, it is generally desirable that the output impedance of the power amplifier is small and the damping coefficient is large. . The damping coefficient is generally between tens to hundreds, and the damping coefficient of the power amplifier can be as high as 200 or more.

L5, equal loudness control

　　 Its function is to boost high and low frequency sound at low volume. Due to the poor auditory sensitivity of human ears to high-frequency sounds, especially low-frequency sounds, it is required to perform auditory compensation for high and low frequencies at low volume, that is, a large increase in low frequencies is required, and a certain increase in high frequencies is also required. In other words, when the volume is reduced, the lower frequency part of the signal is reduced less than the higher frequency part. Equal loudness control meets this requirement, and equal loudness control is generally 8dB or 10dB.

16. Three-dimensional sound field processing and surround sound

　　 Why do ordinary two speakers make us hear the sound that does not exist as if from behind? Everyone knows that the three-dimensional movie is the illusion produced by the eyes and the production of the three-dimensional sound field cannot be separated from the illusion of the ears. Various hardware 3D audio technologies such as SRS, virtual Dolby, and software 3D technologies such as EAX, A3D, etc., are new technologies launched to reduce costs after fully studying the principle of human ears receiving sound. Essentially speaking, the effect of completing a three-dimensional sound field through multiple speakers is much better than the virtual sound field produced by two speakers. Therefore, surround sound should be based on multi-speaker configuration, which has a strong sense of positioning and space.