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Speaker performance indicators

2021-04-13 85
When it comes to the parameter specifications of the speaker, it has to mention its various performance indicators. Especially if you don't check these indicators when you buy speakers, then you can't judge whether a speaker is good or bad at all. What is the performance index of the speaker? Please follow the author to take a look.

Performance 
1. Frequency range (unit: Hz): refers to the range from the lowest effective sound reproduction frequency to the highest effective sound reproduction frequency. The most ideal reproduction frequency range of the speaker is to reproduce the audible frequency range of the human ear evenly, that is, 20HZ~20000HZ. But in order to replay at a large sound pressure level, the lower the frequency band, the structure that withstands large amplitude and the reduction of distortion must be considered, and the volume of the speaker generally needs to be increased. So the goal should not be too high, 50HZ~16KHZ is enough, of course, 40HZ~20KHZ is better.

2. Frequency response (unit: decibel dB): refers to the connection of a constant voltage output audio signal to the speaker system. When the frequency of the audio signal is changed, the sound pressure generated by the speaker increases or attenuates and phase with the change of frequency The phenomenon that lag changes with frequency, and the corresponding relationship between sound pressure and phase and frequency is called frequency response. The curve of sound pressure changing with frequency is called "amplitude-frequency characteristic", the curve of phase lag changing with frequency is called "phase-frequency characteristic", and the combination of the two is called "frequency response" or "frequency characteristic". The amount of change is expressed in decibels. This indicator is an important indicator for assessing the quality of speakers. The smaller the decibel value, the flatter the frequency response curve of the speaker and the smaller the distortion.

3. Pointing frequency characteristics: the frequency response curve clusters of the speaker measured in the direction of the sound wave radiation at a number of prescribed sound waves, such as the 0 degree, 30 degree and 60 degree directions of the central axis of the sound box. For example, a sound box with good directivity is like a fluorescent lamp, and the light can be evenly distributed to every corner of the room. On the contrary, it is like a flashlight.

4. Maximum output sound pressure level: indicates the maximum sound level index that the speaker can give when the maximum power is input.

Speaker performance indicators


Speaker performance indicators


5. Distortion (expressed as a percentage).
Harmonic distortion refers to the addition of high-order harmonic components that are not in the original signal to the reproduced sound.
Intermodulation distortion, we know that the speaker is a non-linear device. In the process of replaying the sound source, due to the non-uniformity of the magnetic field of the magnetic gap and the non-linear deformation factor of the supporting system, a new frequency that is not in the original signal will be generated. Component, so when the new frequency signal and the original frequency signal are added to the loudspeaker together, it will be modulated to produce another new frequency. In addition, the music signal is not a single-tone sine wave signal, but a multi-tone signal. When two signals of different frequencies are input to the speaker at the same time, due to the large amount of non-linear factors, the two signals will be modulated and a new frequency signal will be generated. Therefore, in addition to the original signal, there are two For new frequencies that are not in the original signal, this distortion is intermodulation distortion. Its main influence is pitch (also known as pitch).
Transient distortion, the transient distortion of the speaker system, refers to a kind of transmission waveform distortion caused by the mass inertia of the speaker vibration system. Due to the certain mass inertia of the loudspeaker, the cone vibration cannot keep up with the instantaneously changing electrical signal, which causes the distortion of the transmission waveform of the reproduced sound, which leads to the change of the frequency spectrum and the timbre. The quality of this indicator is extremely important in the speaker system and speaker unit, and it directly affects the sound quality and the degree of tone reproduction.

Distortion
The concept of speaker distortion degree and amplifier distortion degree is basically the same, except that the amplifier input is an electrical signal, and the output is still an electrical signal, while the speaker input is an electrical signal, and the output is a sound wave signal. Therefore, the degree of distortion of the speaker represents the electrical signal. The amount of distortion that occurs when switching between the signal and the sound signal. Distortion degree index is only a more general term, which should be divided into three types: harmonic distortion, mutual distortion and transient distortion.

6. Marked power (unit: watt W): The power marked on the speaker. Two marking methods are popular in the world:    long-term power or rated power. The former refers to the input of a specified analog signal to the speaker within the rated frequency range, and the signal continues The time is 1 minute, the interval is 2 minutes, and it is repeated 10 times. The maximum input power of the speaker without thermal damage and mechanical damage. The latter refers to the input of a frontier sine wave signal to the speaker within the rated frequency range, the signal duration is 1 hour, the speaker does not produce the maximum sine power of thermal damage and mechanical damage.
The maximum withstand power is the music power (MPO), which originated from the German Industrial Standard (DIN), and refers to the short-term maximum power that the speaker can withstand. This is because when the music signal is played, the amplitude of the audio signal changes greatly, and sometimes the peak value of the music power may exceed the rated power several times in a short period of time. The power labeling standards established by my country's national standard GB9396-88 include maximum noise power, long-term maximum power, short-term maximum power, and rated sine wave power. Usually speaker manufacturers use long-term power or rated power as the marked power of the speaker.

7. Nominal impedance (unit: ohm Ω): refers to the ratio of the signal voltage U of the speaker input to the signal current (this is the same as in high school physics, R=U/I). Because the impedance of the speaker is a function of frequency, the magnitude of the impedance value also changes with the frequency of the input signal. The preferred values of speaker impedance specified by my country's national standards are 4Ω, 8Ω, 16Ω (the recommended value of international standards is 8Ω), and the nominal impedance of the speaker is specified as the lowest value between the peak value F0 of the speaker resonance frequency and the second resonance peak F1 Impedance value. Some foreign speaker manufacturers use a section where the impedance characteristic curve tends to be flat as the speaker's nominal impedance. The nominal impedance of the speaker is different from the nominal impedance of the speaker, because there is more than one speaker unit in the speaker, the nature of each unit is different, and there are series or parallel crossover networks, so the standard stipulates that the minimum impedance must not be Lower than 80% of the nominal impedance value.

impedance
This index represents the ratio of the voltage to the current of the input signal of the speaker. Generally, the input impedance of the speaker can be divided into two categories: high impedance and low impedance. Among them, the speaker speakers higher than 16 ohms belong to the high impedance level, and they are lower than 8. The speakers of European speakers are of low impedance level, and the standard impedance of speakers is usually 8 ohms.

8. Sensitivity (unit: decibel dB): The sensitivity of the speaker is the sound pressure level (sound pressure level) measured at a distance of 1m from the geometric center of each speaker unit on the front of the speaker when the input power to the speaker in the speaker system is 1W. The pressure is proportional to the amplitude and frequency of the sound wave, and the sound pressure level is an indicator of the relative magnitude of the sound pressure). What needs to be particularly pointed out here is that although sensitivity is an indicator of speakers, it has nothing to do with sound quality and tone. It only affects the loudness of the speakers. You can increase the input power to increase the loudness of the speakers.
Sensitivity refers to the sound pressure level measured at 1m in the axial direction when a pink noise signal voltage equivalent to 1W power on the rated impedance is applied to the speaker. The sensitivity of a speaker has no decisive influence on sound reproduction. Because people can get enough volume by adjusting the output of the amplifier. However, in speaker production, the sensitivity of the speaker is a parameter worthy of attention. The sensitivity of each speaker unit must be basically the same in the frequency band responsible for playback, so as to balance the high, medium and bass of the entire speaker during playback.

Speaker performance indicators
Especially for stereo speakers, the units used for the left and right channels must be strictly screened and matched. It is required that the output sound pressure level difference of the unit used by the left and right channels should be within plus or minus 1dB, otherwise it will affect the sound image positioning. The sensitivity of professional speakers is above 95dB/m.w, even as high as 120dB/m.w. The sensitivity of home speakers is small, even if it can have 92dB/m.w, it is very large.

9. Efficiency (expressed as a percentage): The efficiency of a speaker is defined as the ratio of the sound power output by the speaker to the electric power input (that is, the percentage of sound-electric conversion). Recently, the speakers on the market are usually marked with sensitivity, while some speakers are marked with efficiency, but expressed in decibels. This wrong way of labeling has caused some consumers to confuse the two indicators of sensitivity and efficiency. The two indicators of speaker sensitivity and efficiency have nothing to do with sound quality and timbre, nor are they standards for quality assessment. However, the sensitivity and efficiency are too low and the input power of the power amplifier must be increased to achieve the required sound pressure level.
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