How to choose car speakers? Speaker indicator and parameter reference introduction

A lot of female friends buy audio, only look at the "face" without looking at the parameters. Because of the face of a bunch of incomprehensible parameters, it feels like the head is exploding. Xiaobian collected a dry goods. After reading this article, you will know how to look at the indicators and parameters of the speakers.
I believe that for many speakers Xiaobai, how to look at the sound of the speaker is a huge big problem. A lot of female friends buy audio, only look at the "face" without looking at the parameters. Because of the face of a bunch of incomprehensible parameters, it feels like the head is exploding. Xiaobian collected a dry goods. After reading this article, you will know how to look at the indicators and parameters of the speakers.

1, active speakers

Active speakers are speaker systems with power amplifiers (ie amplifiers). The power amplifier and the speaker sounding system are integrated into one body, and can be directly matched with a general sound source (such as a Walkman, a CD player, a DVD player, a video recorder, etc.) to form a complete sound combination. With active speakers, there is no need to purchase a power amplifier, no longer a reasonable choice of power amplifiers, speakers, easy to operate, its high performance and price ratio, generally accepted by the working class.

2, box classification

According to the principle of sound generation and internal structure, the speakers can be divided into inverted type, closed type, flat type, horn type, labyrinth and other types, the most important forms of which are closed and inverted. Closed speakers are equipped with speakers on a closed box, which is relatively inefficient. The inverted speaker is different from the circular inverting hole on the front or rear panel. It works according to the principle of the Helmholtz resonator. It has the advantages of high sensitivity, high power capability and wide dynamic range.

Because the sound waves on the back of the speaker are also released from the phase guiding holes, the efficiency is also higher than that of the closed box. Moreover, the same speaker installed in a suitable inverter box will be 3dB higher than the low-frequency sound pressure obtained in the same volume of the closed box, which is beneficial to the performance of the low-frequency part, so this is also a wide range of inverter boxes. An important reason for the popularity.
3, power

There is no direct relationship between the sound quality of the speaker and the power. The power determines the maximum sound intensity that the speaker can emit. It feels like how loud the sound from the speaker can be. According to international standards, power has two methods of labeling:

Rated power (RMS: sine wave rms) is the maximum electrical power required to drive a 8 Ω speaker within the rated range to dictate the waveform's continuous analog signal, after a certain interval and repeat a certain number of times, without any damage to the speaker;

Instantaneous peak power (PMPO power) is the maximum power that the speaker can withstand for a short period of time.

The US Federal Trade Commission set the standard for power calibration in 1974: driving an 8Ω speaker load with two channels, and measuring the effective wattage when the harmonic distortion is less than 1% in the range of 20 to 20000 Hz, which is the amplifier's Output power, the indicated power is the rated output power. Usually, in order to cater to the consumer psychology, the merchants mark the instantaneous (peak) power, which is about 8 times of the rated power. Imagine the same TDA1521 power amplifier chip with PHILIPS (maximum rated power 30W, THD=10%), and some products are nominally 360W, even 480WP.MPO, is this possible? Does it make sense? So buy multimedia The speaker should be based on the rated power.

The power of the speaker is not the bigger the better, the application is the best. For the average household user's room of 20 square meters, the true 60W power (the effective output power of the speaker is 30W×2) is enough, but The larger the reserve power of the power amplifier, the better, preferably more than twice the actual output power. For example, if the output of the speaker is 30W, the power of the amplifier is preferably greater than 60W. For the HiFi system, the power of the amplifier that drives the speaker is very large.

4, frequency range and frequency response

Frequency range: refers to the range between the lowest effective playback frequency and the highest effective playback frequency that the sound system can play back.

Frequency response: refers to the phenomenon that when a sound signal outputted by a constant voltage is connected to the system, the sound pressure generated by the speaker increases or decreases with frequency, and the phase changes with frequency. The relationship (variation) associated with phase and frequency is called the frequency response in decibels (dB).

The frequency characteristics of the sound system are often described by the ordinate of the decibel scale representing the power and the frequency response curve of the frequency represented by the abscissa of the logarithmic scale. When the sound power is 3 dB lower than the normal power, this power point is called the high frequency cutoff point and the low frequency cutoff 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”, respectively. characteristic". This is an important indicator to check the performance of the speaker. It has a direct relationship with the performance and price of the speaker. The smaller the decibel value, the flatter the frequency response curve, the smaller the distortion and the higher the performance. Such as: a speaker frequency response 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. Sounds below 20 Hz, although not heard, but other human sensory organs can be perceived, that is, the so-called bass strength can be felt, so in order to perfectly play various instruments and language signals, the amplifier must achieve high fidelity goals. The harmonics of the tones are reproduced. Therefore, the frequency band of the amplifier should be extended, the lower limit should be extended below 20 Hz, and the upper limit should be increased to above 20,000 Hz. The representation of the frequency response of the signal source (receiver, recording deck, and CD player) is different. For example, the frequency response of the FM stereo broadcast specified by the European Broadcasting Union is 10/-2dB when the frequency is 40~15000Hz. The minimum frequency response specified by the International Electrotechnical Commission for the recording studio is: 10/-2.5/4.5dB (40°C). With), the actual achievable indicators are significantly higher than this value. The upper limit of the frequency response of the CD player is 20000 Hz, and the low frequency end can be made very low, only a few Hertz, which is one of the reasons for the good sound quality of the CD player.

However, the harmonic components that make up the sound are very complicated. The wider the frequency range, the better the sound is, but this is basically correct for medium and low-end multimedia speakers. In the labeled frequency response, we usually see the terms "system frequency response" and "amplifier frequency response". We must know that the "system frequency response" is always smaller than the range of "amplifier frequency response", so only the label is marked. "Amplifier frequency response" does not make any sense, it is only used to deceive some unsuspecting consumers. Nowadays, the speaker manufacturers generally have a wide range of system frequency response, and there are not many high-frequency parts, but the annotation on the low end is extremely unreal. The foreign famous HiFi (high-fidelity) speakers are also marked with 4, 50Hz or so. And the domestic two or three hundred wooden ordinary speakers actually dare to mark this data, it really makes people laugh at the big teeth! So please tell everyone that the low-band sound must be heard, do not easily believe the value on the leaflet. The music in the multimedia speaker is mainly based on the music, songs, sound effects of the game, background music and the vocal and environmental sound effects in the movie. These sounds are mainly medium and high sounds, so when selecting multimedia speakers It should be more focused on its ability to express sound in the mid-to-high range, rather than the low frequency band. If you really want the cinema effect, then a powerful subwoofer can definitely meet your needs.

Loudness

The strength of the sound is called the intensity, which is determined by the magnitude of the rapidly changing air pressure (sound pressure). However, the subjective feeling of the human ear is not consistent with the objective actual intensity. People regard the subjective feeling of strength as the loudness, and the unit of measurement is also decibel (dB), which is based on the sound of 1000Hz sound at different intensities. The ratio of pressure is determined by l/10 of its usual logarithm. The reason for taking the logarithm value is because the increase in intensity and loudness is not proportional to the relationship between the true number and the logarithm! For example, when the sound intensity is as large as 10 times, it sounds like a level (10dB), and the intensity is large enough. At 100 times, it sounded like two levels (20dB). For a 1000 Hz sound signal, the minimum sound pressure that the human ear can feel is 2×10E-5Pa, and the sound pressure level is set to 0 dB. When the sound pressure exceeds 130 dB, the human ear will be intolerable, so the dynamic range of the human ear hearing is 0 to 130 dB.

People have different sound perceptions 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 hearing frequency range; the frequency f<16-20Hz and f >18 ~ 20KHz sound, no matter how high the sound level, the human ear can not hear. Therefore, the auditory frequency of the human ear is 20Hz ~ 20KHz, this frequency band is called audio or audio; regardless of the sound pressure level, the human ear is most sensitive to the sound of 3KHz ~ 5KHz frequency.

Most people can't feel the signal sound level abruptly less than 3dB, so the sound system often uses 3dB as the allowable frequency response curve variation range.

5, distortion

There are harmonic distortion, intermodulation distortion and transient distortion. Harmonic distortion refers to the distortion caused by the higher harmonic components that the original signal does not have in the sound playback; the intermodulation distortion mainly affects the tonal aspect of the sound; the transient distortion is due to the existence of a certain inertial mass of the speaker. The vibration of the basin cannot keep up with the difference between the original signal and the playback sound caused by the vibration of the instantaneously changing electrical signal. It is more important in the speaker and speaker system, which directly affects the degree of restoration of the sound quality, so this indicator is closely related to the quality of the speaker. This is often expressed as a percentage, and the smaller the value, the smaller the distortion. The distortion of ordinary multimedia speakers is preferably less than 0.5%, and usually the distortion of the subwoofer is generally large, and less than 5% is acceptable.

6, the sensitivity of the speaker (in dB)

The sensitivity of the speaker is 3dB, and the sound pressure of the output is doubled. Generally, the sensitivity is 87 dB, the sensitivity is below 84 dB, and the sensitivity is above 90 dB. The increase in sensitivity is at the expense of increased distortion, so as a high-fidelity speaker, it is necessary to reduce the sensitivity requirements for the reproduction and reproduction of the tone. But it can't be said that the sound quality of the speaker with high sensitivity must be bad, and the speaker with low sensitivity must be good. Speakers with low sensitivity are difficult to push (requires a large power reserve for the amplifier). Therefore, although the sensitivity is an indicator of the speaker, it has nothing to do with the sound quality of the speaker.

7, impedance

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

The impedance of the headphones is generally high impedance - 32 ohms are common. The impedance of the amplifier can generally be labeled as an equivalent impedance, such as an output of 130W at 4Ω, which is roughly equivalent to an equivalent output of 80W.

There is a term that is easily confused with the term "damping coefficient", which refers to the speaker impedance divided by the internal resistance of the amplifier source, which ranges from approximately 25 to 1000. The speaker cone is oscillated several times after the electrical signal has disappeared to completely stop the oscillation, and the voltage generated by the coil generates current and magnetic field to prevent this parasitic motion, which is damping. The magnitude of the current, that is, the effect of the damping, depends on the internal resistance of this current flowing through the output stage of the amplifier. This resistance is much lower than the rated impedance of the speaker, typically 0.1Ω, but due to the series resistance and frequency division of the speaker voice coil. The existence of the series resistance of the network, the damping coefficient is difficult to achieve 50.

8, signal to noise ratio

It 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 expressed in dB. For example, a tape recorder has a signal-to-noise ratio of 50 dB, which means that the output signal power is 50 dB greater than the noise power. The higher the signal to noise ratio, the lower the noise.

The minimum requirements of the International Electrotechnical Commission for signal-to-noise ratio are 63dB for the preamplifier, 86dB for the post amplifier, and 63dB for the combined amplifier. The optimal value of the combined amplifier signal-to-noise ratio should be greater than 90dB; the radio head: 50dB of FM stereo, actually better than 70dB; 56dB (common band) of the tape recording seat, but the signal noise after Dolby noise reduction There is a big improvement. If the noise-to-noise ratio after Dolby B noise reduction can reach 65dB, the signal-to-noise ratio of Dolby C can be up to 72dB after noise reduction (all of them refer to ordinary bands); the signal-to-noise ratio of CD machine can reach more than 90dB, high-grade It can reach more than l10dB. When the signal-to-noise ratio is low, the noise is small when inputting small signals, and the sound of the entire range is obviously opaque, so speakers with a signal-to-noise ratio lower than 80 dB are not recommended for purchase. The subwoofer of 70 dB subwoofer is not recommended for purchase. .

9. The structure and characteristics of the speaker

The speaker can be divided into a bookshelf type and a floor type according to the structural form. The former is small in size, clear in level, and accurate in positioning, but the power is limited, and the extension and the sense of quantity in the low frequency band are insufficient, and it is suitable for enjoying music hobbies mainly based on high fidelity music. And also the first choice for our multimedia enthusiasts;

The latter is large in size and bears a large amount of power. The sense of low frequency is strong and flexible. It is good at expressing the imposing momentum and powerful shock, but it is not good enough for layering and positioning. For lovers of different music, this is also an important part that should be understood before purchasing.

K Rated Transformer

Applications:

The use of a K-rated transformer is anywhere non-linear loads are present. Prime uses would be in factory automation, computer rooms, and office buildings because of the high harmonic content in these areas, Typically a K-13 rated transformer is sufficient for most applications. UL recognizes K-factor values of 4, 9, 13, 20, 30, 40 and 50. The K-factor number tells us how much a transformer must be de-rated to handle a definite non-linear load or, conversely, how much it must be oversized to handle the same load.


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