How to determine the advantages and disadvantages of speakers from the perspective of technology and application

In the entire audio (including computer multimedia speaker) system, the speaker is used as the replay Tool of the audio system. It is the simplest but the most complicated equipment. Because it is responsible for electro-acoustic conversion equipment, the playback effect is directly related to the quality of the entire system, so whether the sound box is properly selected is an important factor in determining whether a sound system can be matched and built successfully. To determine the pros and cons of a pair of speakers, it is usually carried out from two aspects: technical indicators and human subjective listening evaluation. The author gives a brief introduction to the intermediate level of this article for the reference of friends when building their own sound system. ?

First, the main technical indicators of Hi-Fi speakers?

The International Electrotechnical Commission (IEC) has formulated a set of minimum standards for Hi-Fi speakers for home use. The standard document code is IEC-581-7. With the minimum standard, you can more objectively determine whether the speaker is qualified. Some minimum standards of IEC-581-7 for household Hi-Fi speakers are:

(1) Frequency characteristics: at 50Hz-12500Hz, the deviation is within + 4 ~ 8dB; in the frequency band of 100Hz ~ 8kHz, the deviation is ≤ ± 4dB;

(2) Pointing characteristics: horizontal plane ± 30? O, vertical plane ± 10? O, deviation of frequency response curve from positive axis ≤ ± 4dB;

(3) The inconsistency of the left and right channel speakers: the difference of the average sound pressure in the range of 250Hz ~ 1kHz ≥ 2dB;

(4) Total harmonic distortion: ≤2% at 250Hz ~ 1kHz, ≤1% -2% at 1Hz ~ 2kHz, ≤1% at 2kHz ~ 6.3kHz;

(5) Impedance: within the range of 20Hz ~ 20kHz, ≥80% of rated impedance;

(6) Allowable power: ≥10W. ?

From the above standards, it is not difficult to see that the technical requirements of speakers that comply with the IEC Hi-Fi standard (high-fidelity) are not very high. Nowadays, speakers produced by regular manufacturers on the market can basically meet or exceed these standards. So among these many qualified products, how to determine whether a pair of speakers is excellent from the technical indicators? I think the speakers are excellent? Several indicators. ?

The frequency response range refers to the range of the frequency band in which the sound box can replay, generally expressed in Hz to kHz. Since the limit range of the human ear for frequency audibility is 20 Hz to 20 kHz, as the age increases, the hearing of the human ear will drop to about 25 Hz to 16 kHz. Therefore, as a pair of excellent speakers, the frequency response range must of course reach or exceed this range. ?

The pointing characteristic shows the change of the output sound pressure level when the speaker deviates from the front axis, and it has a great influence on the width and positioning of the sound field. However, the directivity of the loudspeaker (mainly refers to the mid-high frequency unit) is not as wide as possible. Professional products have certain requirements. The directivity of the well-designed unit (mainly the horn type) can be controlled within the specified range, and the sound pressure level drops less 6dB. General dome and paper cone units cannot, and their directivity gradually narrows with increasing frequency. In order to meet the requirements of the pointing characteristics, the requirements for the unit used are: if it does not decrease by 4dB in the direction deviating from the positive axis by 30? O, then the crossover frequency f and the equivalent radius a of the cone must meet f≤ 140 / a, such as the crossover frequency of a 200mm (8 inch) diameter speaker must be below 1650. Of course, some advanced and well-designed speaker units can also set the crossover point to be higher than the theoretical value, but whether it is a low, medium, or high frequency speaker, you must consider this point when choosing the caliber, crossover point, and power ( Two frequency division is particularly important), many two frequency division speakers only take the power capacity of tweeters into account when dividing the frequency, and achieve a high crossover point, ignoring the requirement of directivity, this system is often only on the front axis of the speaker. It has a good frequency response, and after deviating from the axis, the frequency response becomes worse, affecting the width and positioning of the sound field. ?

Sensitivity refers to the efficiency of electro-acoustic conversion of the speaker, usually expressed in sound pressure dB / W / m or dB (decibel). The meaning of this indicator is that when the power of 1 watt is input to the speaker, it is on the positive axis 1 meter away from the speaker The amount of sound pressure obtained. Hi-Fi playback requires a maximum output sound pressure of 110dB, which requires the speaker to have a high sensitivity and a certain power margin, preferably greater than 88dB, so there are at least two benefits. First: the power amplifier The power capacity requirements of the speaker and the speaker are reduced, and the cost of both is reduced (for the sensitivity of 88dB, the output sound pressure level of 110dB must be reached, and the input power of 160W is required. For every 3dB increase in sensitivity, the power required to reach the 110dB sound pressure level decreases Times); second: can reduce distortion. To achieve the same sound pressure level as the high-sensitivity output, low sensitivity requires more power and amplitude, but this will increase the nonlinear distortion and reduce the life of the speaker. Relatively speaking, the better speaker sensitivity is above 86dB. At this time, they will not have any problems with the amplifier with a rated output power of only 50W, but it is not that the speakers with low sensitivity are not good, like some classic foreign Hi -End speakers, such as LS 3 / 5A and ATC SCM-20, have a sensitivity lower than 85dB. Therefore, as far as this indicator is concerned, of course, the bigger the better. Because speakers with high sensitivity input the same power, the obtained sound pressure will be greater than speakers with low sensitivity. Conversely, under the same sound pressure, the power requirements of the amplifier are lower than those with low sensitivity. small. Therefore, sensitivity is an important technical indicator to evaluate whether a pair of speakers is easy to promote. ?

Withstand power refers to the power value that the speaker can withstand without causing excessive distortion. If the input to the loudspeaker continuously exceeds the rated power (RNS), the loudspeaker will not only be distorted, but also be in danger of being burned. Therefore, the larger the indicator, the better. However, in practical applications, the chance of a speaker with an RMS of 100W burning out is equal to zero, because the human ear can't bear the sound pressure it brings before reaching this indicator. In multi-way crossover speakers, the chance of being easily burned is also greatly reduced. Therefore, when choosing a speaker, in addition to paying attention to the withstand power of the speaker, also pay attention to what materials and structures are used to manufacture the tweeter. ?

Impedance refers to the resistance of the speaker to alternating current. It consists of three parts: resistance, capacitive reactance and inductive reactance. It is the reference value for calculating the power supplied by the amplifier. Because the impedance of the speaker changes with the change of frequency, the value marked by the manufacturer to the speaker is actually an average value. This should also be paid attention to when using speakers. The impedance of common household speakers nowadays is generally 8 ohms, 6 ohms and 4 ohms. ?

The impedance of modern speakers tends to be small. The impedance of the speakers becomes smaller. The advantage is that more energy can be obtained from the amplifier. This means that the impedance is small when the input power and sensitivity are not different. The sound from the speaker will be louder than the sound from the speaker with high impedance. ?

When a pair of speakers and an amplifier are used together, the chance of matching problems is extremely small (especially the transistor machine). However, when using an amplifier to drive two pairs of speakers, care should be taken to avoid the inconsistency of the impedance of the two pairs of speakers (such as a pair of 8 ohms, a pair of 4 ohms) and the impedance of the two pairs of speakers are below 4 ohms, otherwise, It is easy to cause the amplifier to burn down in an approximate short circuit. ?

As for the consistency index of the left and right channels, it is rarely marked on the manual. From an empirical point of view, most common products cannot meet this requirement, but this index has a great relationship with the accurate reproduction of the sound field and sound image localization. When we buy, it is best to buy some reputable brand products, preferably the paired products of the left and right channels. Generally, such products are indicated on the production number of the speaker. ?

Second, subjective (listening) evaluation?

To judge the quality of a pair of speakers, although a certain answer is obtained from the technical indicators, people buy speakers or other audio equipment just to get good sound rather than dry technical indicators, and good technical indicators are not equal to With a good voice, just as the beginning of the CD, no one can deny that it far exceeds the LP turntable in technical indicators. However, due to the shortcomings of the hard, sharp and non-musical sound of the early CD player, it attracted many people's criticism. As far as the speaker is concerned, there are also such problems. For example, the famous LS3 / 5A has a sensitivity of only 82dB and an impedance of up to 11 ohms. In terms of technical specifications, it is a pair of speakers with very low efficiency, but It is the most famous monitor speaker in history. Because of its extraordinary vocals and string, it has also been widely welcomed. From the above example, we can see that the evaluation of audio equipment is based on technical indicators to judge its pros and cons. It is also one-sided, plus people have different preferences for audio sound, so in the purchase of speakers, especially some early When it comes to finalizing excellent products, it seems to have become more important to be satisfied with hearing. ?

An important aspect of subjective listening evaluation of speakers is the accuracy with which the original sound can be reproduced. The strict definition of accuracy is that under the constraints of a certain price and speaker size, the tone details, dynamic range and sense of surround of the original sound recording should be reproduced in the widest possible frequency range, even if there is a difference. ?

In order to ensure the accuracy of the listening evaluation results, you must seize every opportunity to listen to and compare the differences in the sound output of different speakers. At the same time, you should use high-quality amplifiers and high-level audio equipment to put different speakers at the same volume. 3. Listening evaluation under the same position to reduce the changing factors during the evaluation. Since the software theme used has a great influence on the results of the listening evaluation, when choosing the music recording for presentation, you should not only focus on how beautiful the music itself is, but also pay attention to its recording accuracy and its ability to highlight the sound quality. Some aspects of the requirements. ?

When summarizing subjective listening, there are roughly the following four criteria:

1. Sound uniformity?

The uniformity of timbre is the most important in speaker evaluation. The speaker should have a uniform and true timbre expression in the entire frequency range from bass to treble. To evaluate the entire sound range as a whole, it is generally divided into four sections:

A. Irregularity in the bass / middle bass range. The most telling point is whether the bass performance is buzzing or weak, or whether it is boring or hollow. ?

B. Fluency of the vocal range. The human voice includes the speech sound of the speech and the singing voice of the actor. Pay attention to whether there is intermediate frequency staining when listening to the evaluation. This is the weak point that the speaker is easy to have. The performance is that the timbre is not constant, the human voice quality is degraded, and the sound produced has serious nasal sounds, humming or rough harshness, hollowing, etc. ?

C. Fluency in the treble range (frequency band around 2500 Hz to 13 kHz). The string part of the large orchestra Zhu team should be selected for listening evaluation, and pay attention to whether there is any unnaturalness in the string sound or the sound is dry or excessively sticky. The quality of the people who can correctly participate in this frequency band requires high quality, and requires a very skilled listening ability for the live string performance part. It is best to ask some experienced fans to help. ?

D. Performance in the ultra-high range (frequency band above 13kHz). Pay attention to listening to the vocal effects of jazz or rock east pull. The test CD should contain clear and repeated transient parts. Pay attention to carefully listen to the expression of each speaker for fuzzy features, splitting sounds and a rustling sound. Instead of crisp metallic sounds, these all indicate uneven defects on the surface of the tones in the treble range. ?

2. Dynamic range?

Almost all speakers will compress the dynamic range of the sound source. The obvious way to limit the dynamic range is to produce audible distortion, such as frequency domain imbalance, high and low frequency disjoint, etc. Usually bass and midrange sounds hum, hack or crackle with too loud sound. Another limited form of dynamic range that is difficult to detect is the non-linear response, which is manifested by the fact that under the driving of extremely high volume, the mid-to-high range part sends a larger volume of output than the low-frequency part than the low-frequency part, generating a powerful, wide-band instantaneous impact . Due to the rumbling sound from the woofer, it is not certain whether the speaker distortion is caused by vibration of furniture, floor or window, nor is the sound enhancement phenomenon caused by the speaker, or the distortion that the human ear naturally generates at extremely high volume, This can only be determined by repeated listening evaluations over a long period of time in a very familiar listening environment. ?

3. Bass expansion capability?

Very few speakers can really reproduce frequencies as low as 20Hz or 25Hz, and it is very rare that the energy of the recording content is concentrated in the frequency band below 40Hz. Using the large bass drum in classical music and the subwoofer synthesizer in popular music is the best signal source to judge the bass extension ability. However, it is difficult to determine the subwoofer response capability of the speaker without listening in the actual environment at home. Because the placement of the speaker and the acoustic characteristics of the room have a much greater impact on the bass performance of the speaker than the characteristics of the speaker itself. ?

Considering the above situation, one or several very familiar recording contents can be used to listen to the speaker's bass expansion ability. The content should include a percussion instrument with a relatively dynamic range, and a piece of music that can easily make people feel the subwoofer recording effect. Low-frequency sound performance. ?

4. Sound image localization ability?

Sound image localization refers to the sense of position and depth of sound on the space stage. The sound image localization ability is the most variable and the most difficult indicator for listening speakers. ?

Listening to locusts should pay attention to the stability of sound image localization. For example, whether the position of the band actor has drifted with the increase or decrease of the music frequency. Can the sound stage fill the space between the two speakers or extend to the two sides beyond the distance between the speakers? Can it only be kept in the middle of the two speakers? Are the front and back depths of the instruments and vocals naturally unfolded? Is it excessive? Exaggerated reverberation phenomenon?

Different types of speakers have different sound image localization characteristics. For example, dipole and most electrostatic and planar magnetic pole design speakers usually create enhanced depth and space at the expense of; ordinary speakers are somewhere in between. ?

After understanding the main points of the above-mentioned listening evaluation, it should also be noted that the speakers produced in different countries and regions also show different sound characteristics due to the influence of local cultural factors. In theory, an ideally designed speaker should be suitable for various genres of music, faithfully replay the original sound, without increasing or reducing the signal content, but there are fewer speakers that can really achieve neutral sound. At the same time, it is theoretically believed that the flatter the frequency response curve of the speaker, the better. However, in fact, the sound of a flat frequency response speaker is not necessarily beautiful. Most speakers have ups and downs in certain frequency bands. The curves of different speakers are different. This also formed the style of sound. ?

For example, speakers produced in the United States generally have lively, bold and hearty sound characteristics. American sound is divided into two kinds of east coast sound and west coast sound. The representatives of east coast sound are AR, THIEL, AVALON, Hales, Cello and Boston and other brands. This kind of speaker generally pays more attention to the accurate reproduction of the sound, showing a tendency that is more suitable for playing orthodox music, and can create a deep and wide sound field. The overall tone is a bit similar to the British sound, but the sound is more Energetic and analytical, the above-mentioned brands have become the new representatives of American speakers. The speakers produced by JBL and Alter are the representatives of West Coast Sound. Under the influence of Hollywood, the sound of this speaker is particularly crisp, bright, and powerful. When listening, it often gives people a strong sense of functional stimulation. Their sales target It is mainly those who like rock, jazz and pop music. In recent years, the sound of the West Coast speakers has tended to be aligned with the East Coast. ?

The vast majority of British equipment generally has the characteristics of sweet sound, warmth, less sound staining and rich musical taste. It should be said that this is a sound suitable for listening to classical music. Since most speakers in the UK are manufactured in compliance with BBC standards, they are also more assured in quality. In addition, the small bookshelf speaker is also a product that the British are very good at. ProAc, Rogers, ATC, AE, KEF, B & W, Tannoy, Mission and other famous brands are more representative. ?

In the past two years, European voices have been dubbed as "Various styles". European voices can be divided into Northern Europe and Southern Europe. Most Nordic products are influenced by French products. The voice exudes a fresh and bright romantic atmosphere unique to the French At the same time, it also has its uniqueness in the description of music details. The more representative brands are LMLab and Dali. The products of Southern Europe are represented by Italy, and their sound characteristics are warm and charming, and the sense of quantity is sufficient. The representative products are the famous Sonus faber, while the speakers of Germany, Sweden, and Denmark have a sound characteristic of sound and less dyeing, and the products are Dynaudio. , Jamo, etc. ?

The early Japanese speakers mostly followed the West Coast products of the United States, mostly emphasizing the contrast between high and low frequencies. It would feel very stimulating at first listening, but listening for a long time is easy to make people tired. With the continuous improvement of Japanese speaker manufacturing technology and the change of the world audio market structure, some small and medium-sized speakers in Japan such as Victor, JVC's SX-V1, SX-V7, Pioneer's S-LH5 and Diat one's DS- A5, etc. are good in performance and price ratio, and gradually change in sound in the direction of high analysis, energy and accurate reproduction of sound characteristics.
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