Speaker types and performance indicators
The speaker is also called the speaker system, which is an extremely important part of the audio system. Because the sound quality of the speakers has a great impact on the entire sound system. At present, the level of program signal source equipment and power amplifiers has been done very high, so a sound system composed of high-quality audio sources, high-quality amplifiers and speaker systems, its playback quality mainly depends on the speakers.
One, the type of speakers
There are many ways to classify speakers. Common classifications in professional audio are as follows:
1. According to the occasion of use: divided into two categories: professional speakers and home speakers. Household speakers are generally used for home playback. They are characterized by delicate and soft playback sound, more delicate and beautiful appearance, not high playback sound pressure level, and relatively little power. Professional speakers are generally used in professional entertainment venues such as dance halls, karaoke halls, theaters, halls and stadiums. Generally, professional speakers have high sensitivity, high playback sound pressure, good power, and high power. Compared with home speakers, their sound quality is harder and their appearance is not very delicate. However, the performance of monitor speakers in professional speakers is similar to that of home speakers, and their appearance is generally more exquisite and compact, so this type of monitor speakers are often used in home Hi-Fi audio systems.
2. According to the audio frequency: can be divided into full-band speakers, subwoofer speakers and subwoofer speakers. The so-called full-band speaker refers to the sound that can cover the low frequency, intermediate frequency and high frequency range. The lower limit frequency of the full-band speaker is generally 30Hz-60Hz, and the upper limit frequency is 15KHz-20KHz. In general small and medium-sized audio systems, only one or two pairs of full-band speakers can be used to fully take on the playback task. Bass speakers and subwoofers are generally dedicated speakers used to supplement the low-frequency and ultra-low frequency playback of full-band speakers. This type of speaker is generally used in large and medium-sized audio systems to enhance the strength and shock of low-frequency playback. When in use, after frequency division by an electronic crossover (crossover), the low-frequency signal is sent to a special bass power amplifier, and then the bass or subwoofer speakers are promoted.
3. Divided by purpose: generally can be divided into main speakers. Monitor speakers and return speakers, etc. The main sound box is generally used as the main sound box of the sound system to undertake the main sound reproduction task. The performance of the main playback speaker has a great impact on the playback quality of the entire audio system, and a full-band speaker plus a subwoofer speaker can also be used for combined playback.
Monitor speakers are used for program monitoring in control rooms and recording studios. They have the characteristics of small distortion, wide and flat frequency response, and little modification of the signal, so they can most truly reproduce the original appearance of the program. Back-to-listening speakers, also known as stage monitor speakers, are generally used on the stage or dance hall for actors or band members to monitor their singing or performance. This is because they are located behind the main sound box on the stage, and cannot hear their own voice or the band's performance clearly, so they can't cooperate well or can't find out the feeling, which seriously affects the performance. Generally, the return-to-listening speaker is made of a bevel shape and placed on the ground, so that it can be placed on the stage without affecting the overall shape of the stage, and it can be heard clearly by the people on the stage when the sound is played, and the sound will not be fed back to the microphone. Howling. 4. According to the cabinet structure: it can be divided into sealed speakers, inverted speakers, labyrinth speakers, sonic tube speakers and multi-cavity resonant speakers. Among them, the most used in professional speakers is the inverted speaker, which is characterized by wide frequency response, high efficiency, and large sound pressure, which is in line with the type of professional audio system speakers, but because of its low efficiency, it is less in professional speakers. Application, mainly used for household speakers, only a few monitor speakers adopt a closed box structure. The sealed speaker has the advantages of simple design and manufacture, wide frequency response, and good low-frequency transient characteristics, but it has higher requirements for the dial unit. At present, in all kinds of speakers, inverted speakers and sealed speakers account for the majority of the proportions. Other types of speakers have many structural forms, but they account for a small proportion.
Second, the performance indicators of the speaker system
1) Frequency response (effective frequency range)
This indicator reflects the main frequency range in which the loudspeaker works. When a constant voltage signal source is applied to the speaker and the frequency of the signal source is changed from low frequency to high frequency, the sound pressure generated by the speaker will change with the change of frequency. The resulting sound pressure-frequency curve is the frequency response curve of the speaker. The IEC (International Electrotechnical Commission) stipulates the frequency limit of the sound that the loudspeaker can reproduce, that is, the effective frequency range, which is a frequency range that is 10dB lower than the average sound pressure level of one octave near the peak in the loudspeaker's sound pressure frequency characteristic curve. The wider the range, the better the sound reproduction characteristics
Generally, the minimum required frequency response of high-fidelity speaker boxes is 50-12500HZ (+4~-8dB), which can reach 50-16000Hz is enough. Of course, 30-20000Hz is better.
2) Rated impedance
It refers to the impedance value measured at the input of the speaker at a certain operating frequency (intermediate frequency). It is usually indicated on the product brand nameplate and given by the manufacturer. The impedance characteristics of the speaker. The rated impedance given by the manufacturer is usually the impedance modulus at which the maximum work is expected to be obtained in the rated frequency range. Rated impedance is generally specified as 4 ohms, 8 ohms, 16 ohms, 32 ohms, etc., and 3 ohms, 6 ohms, etc. are also adopted abroad.
The power of the loudspeaker is one of the important indicators for choosing a loudspeaker. It should be pointed out that there is a big difference in the standardization of domestic and foreign loudspeakers, because the definition and interpretation of power are different. The nominal power of a general speaker is the rated power.
Rated power or rated noise power refers to the input power when the speaker can work continuously for a long time without producing abnormal sound. In general testing, a pink noise signal is used, and the test is performed within the rated frequency range through a specific filter. According to the IEC standard, the tested loudspeaker should ensure that no abnormality occurs during 100 hours of continuous work. By the way, the American EIA standard stipulates that the test time is 8 hours, and the filter is also different.
The maximum noise power is different from the rated power. It indicates the ability of the loudspeaker to withstand large input power for a short period of time. The test time is only a few seconds or a few minutes. Generally, the maximum noise power is 2-4 times the rated power.
The characteristic 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 and efficiency of the speaker box are two different concepts. The efficiency is the ratio of the output sound power to the input electric power. Generally speaking, the efficiency of the speaker box with high sensitivity is also higher.
The sensitivity of a speaker has no decisive influence on sound reproduction, because people can adjust the output of the amplifier to obtain sufficient volume. However, in speaker production, the sensitivity of the speaker is a parameter worthy of attention. Because in a two-way or three-way speaker, the sensitivity of each speaker unit must be basically the same in the frequency band that is responsible for playback, so that the entire speaker has a balance of high, medium, and bass during playback. 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.
For professional speakers, especially in long-distance sound reinforcement (such as large halls, gymnasiums, etc.), speaker sensitivity is also one of the criteria that must be paid attention to. This is because in order to achieve the same sound pressure level, the power capacity of the rate amplifier can be greatly reduced by using a higher sensitivity. Generally, 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 reach 92dB/m.w, it is very large.
Directivity is used to describe the ability of a speaker to radiate sound waves in all directions in space. It is generally expressed by the curve of the sound pressure level changing with the radiation angle. There are usually two ways of expressing directivity: one is to mark the frequency response curve of the speaker at several angles such as 0 degree, 30 degree, 60 degree, and the frequency response curve can be compared with the frequency at 0 degree. See how the sound pressure level changes. This kind of frequency response curve is called the directivity frequency curve. The other is expressed in polar coordinates. It uses the position of the loudspeaker as the origin and uses polar coordinates to draw the directivity diagram of certain frequencies. From it, the directivity of certain frequencies can be seen vividly. In the Hi-Fi system, it is generally not desired that the directivity of the speaker (or sound box) is too sharp (narrow). Otherwise, people who are close to the main shaft of the speaker will hear better audio effects, and the audio effect will be worse when deviating from the main axis. The scenting range in which the sound of the entire playback frequency band can be heard uniformly is restricted. However, for venue amplification occasions, the directivity of the loudspeaker is very important, because the use of directivity can weaken the feedback effect of the loudspeaker on the microphone, thereby eliminating the howling of the loudspeaker system. In professional speakers, there are many other ways to express directivity.
The directivity of the loudspeaker is related to the frequency. Generally, low frequency (such as below 300Hz) has no obvious directivity. At high frequencies, due to the short wavelength of the sound waves, the directivity will become sharp, so some speakers arrange several high-frequency units in different directions to improve the directivity. The directivity is also related to the caliber of the speaker. Generally, when the caliber is large, the directivity is also sharp; when the caliber is small, the directivity is wider.
The distortion of the speaker system includes wave distortion, intermodulation distortion and transient intermodulation distortion. The distortion characteristics of a speaker are more likely to cause deterioration of the characteristics than a single speaker. Usually near the crossover point, the distortion is greatly increased due to improper design or debugging. Harmonic distortion is mainly generated at low frequencies, especially near the resonance frequency. For high-fidelity speakers, the minimum required harmonic distortion is not more than 2%.