Speaker identification technology method

In the entire audio system (including computer multimedia speakers), the speaker, as a replay tool of the audio system, is a seemingly *simple, but actually *complex equipment. As audiophiles, how should we distinguish between the pros and cons of speakers? The editor below will share the relevant methods for you. Welcome everyone to read and browse.

One, the main technical indicators of Hi-Fi speakers
The International Electrotechnical Commission (IEC) has formulated a set of lower standards for household Hi-Fi speakers. The standard document is coded as IEC-581-7. We only need to look at the speaker’s manual to see if its technical parameters have reached this level. A lower standard can more objectively determine whether the speaker is qualified. Some of the lower standards of IEC-581-7 for home Hi-Fi speakers are

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

(2) Pointing characteristics: horizontal plane ±30?o, vertical plane ±10?o, frequency response curve deviation ≤±4dB compared with the positive axis;

(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: 250Hz～1kHz, ≤2%, 1Hz～2kHz, ≤1%-2%, 2kHz～6.3kHz, ≤1%;

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

(6) (6) Allowable power: ≥10W.

From the above standards, it is not difficult to see that the technical requirements of the (high-fidelity) speakers that meet the IEC Hi-Fi standard are not very high. Now the speakers produced by the regular manufacturers on the market can basically meet or exceed these standards. So in these many qualified products, how to determine whether a pair of speakers are of high quality from the technical indicators? I think the speakers are of high quality? I believe that the speakers* mainly look at the frequency response range, pointing characteristics, sensitivity, power and These indicators of impedance.

Frequency response range refers to the range of sound frequency bands that the speaker can reproduce, generally expressed in Hz～kHz. Since the human ear's audible limit of frequency is 20Hz～20kHz, with age, the hearing of the human ear will drop to about 25Hz～16kHz. Therefore, as a pair of high-quality speakers, the frequency response range must of course reach or exceed this range.

The directional characteristic indicates the change of the output sound pressure level when the speaker deviates from the front axis, which has a great influence on the width and positioning of the sound field. However, the directivity of the loudspeaker (mainly the medium and high frequency unit) is not as wide as possible. Professional products have certain requirements. The directivity of the well-designed unit (mainly horn type) can be controlled within the specified range, and the sound pressure level drop is less than 6dB. The general dome and paper cone units can't do it, their directivity gradually narrows as the frequency increases. To meet the requirements of the pointing characteristics, the requirements for the unit used are: if it does not drop 4dB in the direction deviating from the positive axis by 30°, then the crossover frequency f and the equivalent radius a of the cone must meet f≤ 140/a, for example, the crossover point of a speaker with a diameter of 200mm (8 inches) must be below 1650. Of course, some advanced and well-designed speaker units can also set the crossover point higher than the theoretical value, but whether it is a low, medium, or high frequency speaker, the aperture, crossover point, and power must be considered when choosing ( Two-way frequency is especially important). Many two-way speakers only take into account the power capacity of the tweeter and achieve a high crossover point when dividing the frequency, ignoring the directivity requirements. This system is often only on the front axis of the speaker. It has a good frequency response, and when it deviates from the axis, the frequency response becomes worse, which affects the width and positioning of the sound field.

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

Withstand power refers to the amount of power that the speaker can withstand without causing excessive distortion. If continuous input to the speaker exceeds the rated power (RNS), the speaker will not only be distorted, but also may be burnt. Therefore, this indicator is the bigger the better. However, in actual applications, the chance of a speaker with an RMS reaching 100W from being burnt is zero, because the human ear can no longer withstand the sound pressure it brings before this indicator is reached. In the multi-channel crossover speaker, the chance of being burnt down is greatly reduced. Therefore, when purchasing a speaker, in addition to the power of the speaker, you must also pay attention to what material and structure the tweeter uses.

Impedance refers to the resistance of the speaker to alternating current. It is composed of three parts: resistance, capacitive reactance and inductive reactance. It is the reference value for calculating the power supplied by the amplifier. Since the impedance of the speaker changes with the frequency, the value marked by the manufacturer for the speaker is actually an average value. This point should also be paid attention to when using speakers. Nowadays, the impedance of common household speakers generally has 8 ohms, 6 ohms and 4 ohms. ? The impedance of modern speakers tends to be small. The advantage of decreasing the impedance of speakers is that more energy can be obtained from the amplifier. This also *that is, when the input power is the same and the sensitivity is not much different, the impedance The sound from a small speaker will be louder than the sound from a speaker with a higher impedance. ? When using a pair of speakers and an amplifier, the chance of matching problems is extremely small (especially transistor machines). But when using an amplifier to drive two pairs of speakers, *pay attention to avoiding inconsistent impedances of the two pairs of speakers (such as a pair of 8 ohms and 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 be burnt out by a short circuit. ? As for the consistency of the left and right channels, there are very few indications in the manual. In terms of experience, most ordinary products cannot meet this requirement, but this index has a lot to do with the accurate reproduction of the sound field and sound image positioning. When we buy, it is better to buy some reputable brand products, preferably products with paired left and right channels. Generally, such products are indicated on the production number of the speaker.

2. Subjective (hearing) evaluation

To judge the quality of a pair of speakers, although certain answers are obtained from technical indicators, people buy speakers or other audio equipment only to obtain good sound rather than dry technical indicators. Good technical indicators do not mean With a good sound, just like the beginning of the CD, no one can deny that it far exceeds the LP turntable in terms of technical indicators. However, due to the shortcomings of the early CD player that the sound was dry, sharp, and not musical, it attracted a lot of people's accusations. *In the case of speakers, the same problem exists. For example, the famous LS3/5A has a sensitivity of only 82dB and an impedance of as high as 11 ohms. *In terms of technical indicators, it is a pair of speakers with very low efficiency, but It is the most famous monitor speaker in history. Because of its extraordinary features in presenting vocals and strings, it has also been widely welcomed by people. From the above example, we can see that the evaluation of audio equipment is one-sided to judge its pros and cons based on technical indicators. In addition, people have different preferences for audio sound, so when buying speakers, especially some When it comes to high-quality products, it seems that whether the sense of hearing can satisfy oneself has become more important.

An important aspect of 　　 speaker subjective evaluation* is the accuracy of reproducing the original sound. The strict definition of accuracy is that under the constraints of a certain price and speaker size, the timbre details, dynamic range and enveloping feeling of the original sound recording should be reproduced in the widest possible frequency band, even if there is a difference, it should be small.

In order to ensure the accuracy of the evaluation results, we must seize every opportunity to listen to and compare the differences in the sound reproduction of different speakers. At the same time, we should try our best to use high-quality amplifiers and high-level sound source equipment, and put different speakers at the same volume. , Listening to the assessment in the same position, in order to reduce the factors of change when listening to the assessment. Because the subject matter of the software has a great influence on the results of the listening and evaluation, when choosing the music recording for demonstration, not only should focus on how beautiful the music itself is, but also on its recording accuracy and its outstanding sound quality. Some aspects of the requirements.

In the subjective evaluation, there are roughly the following four criteria:

1. Tone uniformity

Tone uniformity is the most important thing in speaker listening and evaluation. The sound box should have uniform and true timbre expression in the entire frequency domain from bass to treble. The overall evaluation of the entire sound range is generally divided into four sections:

A. Irregularities in the bass/mid-bass range. *The place to explain this problem is to pay attention to whether the bass performance is buzzing or weak, or whether there is a dull hollow sound.

B. The fluency of the vocal range. The human voice includes the voice of speech and the singing of actors, and attention should be paid to whether there is intermediate frequency staining when listening to the review. This is the weakness that the speaker is easy to have. The performance is that the tone is not constant, the quality of the human voice is deteriorated, and the sound produced has a serious nasal, hum, or rough, harsh, hollow sound, etc.

C. The fluency of the treble range (band around 2500Hz ~ 13kHz). The string part of the large-scale orchestral Zhu team should be selected for listening and evaluation. Pay attention to whether there is any unnaturalness in the string sound or where the sound is dry or excessively sticky. The quality of the personnel who can participate in the evaluation of this frequency band is relatively high, and they are required to have a very proficient listening ability for the live string performance. It is better to ask some experienced fans to help.

D. The performance of the ultra-high range (band above 13kHz). Pay attention to the vocal effects of jazz or rock music. The tested CD should contain clear and repetitive transient parts. Pay attention to the expression of each speaker for vague characteristics, cracking, and a rustling sound. Rather than the crisp metallic sound, these all indicate the unevenness of the surface of the super-high 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 the bass and midrange are buzzing, cracking, or popping that is too loud. Another limited form of dynamic range that is difficult to detect is non-linear response, which shows that under the drive of a very large volume, the mid-to-treble part sends out a larger output volume than the low-frequency part than the low-frequency part, resulting in a powerful, wide-band instantaneous impact. . Due to the rumble of the woofer, it is not certain whether the speaker distortion is caused by the vibration of the furniture, floor or windows, and it is also uncertain whether the sound enhancement phenomenon is caused by the speaker or the distortion naturally produced by the human ear at extremely high volume. This can only be confirmed after a long period of repeated listening and evaluation in a very familiar listening environment.

3, bass extension ability

Few speakers can truly reproduce frequencies as low as 20 Hz or 25 Hz, and it is very rare that the energy of the recorded content is concentrated in the frequency band below 40 Hz. Large-scale bass drums in classical music and sub-bass synthesizers in popular music are good signal sources for judging the ability of bass extension. However, it is difficult to determine the subwoofer response ability of the speakers if you don't listen to it in the actual environment at home. Because the placement of the speakers and the acoustic characteristics of the room have a much greater impact on the bass performance of the speakers than on the characteristics of the speakers themselves. Considering the above situation, one or several pieces of very familiar recording content can be used to listen and evaluate the bass extension ability of the speakers. The content should include percussion instruments with a considerable dynamic range, and a music judgment speaker with a super bass recording effect that is easy to make people feel. The low-frequency sound quality performance.

4, sound image localization capability

Sound image localization refers to the position and depth of sound on the space stage. The ability of sound image localization is an indicator that changes greatly and is the most difficult to grasp for listening and evaluating speakers.

Listening to the evaluation of locusts, attention should be paid to the stability of sound image localization. For example, whether the position of the band's actors fluctuates as the frequency of the music increases or decreases. Can the sound stage fill the space between the two speakers or extend beyond the distance between the speakers to the sides? Can it only be centered in the middle of the two speakers? Is the front and back depth of the instruments and vocals unfolding naturally? Is it too much? Exaggerated reverberation phenomenon?

Different types of speakers have different inherent 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; ordinary speakers are somewhere in between. After understanding the above-mentioned listening and reviewing points, it is also important to note that speakers produced in different *regions also exhibit different sound characteristics due to the influence of local human factors. In theory, an ideally designed speaker should be suitable for various genres of music, faithfully replay the original sound, and neither increase nor decrease the signal component, but there are fewer speakers that can truly achieve neutral sound. At the same time, it is theoretically believed that the flatter the frequency response curve of the speaker, the better, but in fact, a speaker with a flat frequency response may not sound as good as it sounds. Most speakers have undulations in certain frequency bands. This also *forms the style of the sound.
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