System Integration Designer Analyzes Speaker Parameters

- Jul 27, 2020-

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The main reason for choosing EAW is that the speaker is among the best among professional speakers, and the reliability of foreign speaker parameters is relatively high, while many domestic speakers have falsely high parameters for project requirements.


First of all, we need to mention the speaker material. The speaker cabinet uses Baltic birch plywood. Because the place is located at a higher latitude and the climate is colder, the trees grow slowly. This also leads to the dense and good texture of the trees here, because the low-frequency signal has a long wavelength. Its corresponding radiation ability is strong and energy is also high. In order to prevent "acoustic short circuit", the stronger the loudspeaker cabinet is, the better. This has also led to the use of porcelain, stone and other hard materials to make the loudspeaker cabinet. Of course, The performance of the low-frequency parameters of such a speaker has been improved, but due to material problems, its tone performance is not good. Secondly, the use of plywood has once again evened the material uniformity of the entire cabinet to a certain extent.


Next, take a look at its specific parameters. Among them, the subsystem item mainly describes the number and size of speaker units. Here I have to talk about the concept of crossover, because the size of each speaker cone is inconsistent, and the intuitive performance of the cone size is The range of frequency response is calculated according to pure theory, and the paper cone is regarded as a mass point, according to the calculation formula of the period of simple harmonic motion:


Assuming that the two speaker cones are of the same material and have a radius of 1 time difference, their area is 4 times different. When the density is the same, their quality is 4 times different. Therefore, the simple harmonic motion period is increased by 2 times, and the corresponding frequency is reduced by 1 time. For example, 12-inch paper cones are twice as low as the 6-inch paper cones. However, if you rely on this method, it is too single. Therefore, there are some multi-unit devices, such as double 12-inch, double 18-inch, etc. These are the use of the principle of coupling to further reduce the lower limit of the low frequency of the speaker. The most significant is the column speaker, as shown below:

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It can be seen that the speaker is composed of a bunch of small units. According to the above, the lower limit of the low frequency of each unit is actually very high, but the lower limit of the low frequency of the speaker is 120Hz, and the principle it realizes is coupling. Popular digitally steerable line array speakers are also suitable.


The previous talk is a bit complicated and complicated. The main thing I want to say is that professional engineers will not pay too much attention to the unit parameter in the speaker parameters, because as long as the speaker parameters are not false, we only need to pay attention to the "frequency response "Scope" is enough, but if you understand the principle, you can look at the size of its unit. First, the size of the speaker in the engineering design is also a very important point. It involves the location of the installation, whether it can be hidden, etc. After the virtual standard parameters of some domestic speakers, if you have experience, you can see it. For example, if a domestic 4-inch ceiling speaker has a frequency response range of 50Hz, you can know it well.


I think a friend who likes to ask questions may raise earphones and say, the earphone is so small, why can the frequency be so low? I won’t explain much here. I just talk about two points. First, the statement we mentioned above is based on the whole diaphragm and the overall rigidity. The structure of the headset is more complicated. It subdivides the inner and outer rings. Second, The earphone is close enough to the ear, and only a small amount of sound energy is needed. The most intuitive low frequency is the perimeter. You only need to design the earphone diaphragm to have a low enough vibration time, and the low frequency signal will naturally come out.


I have said a lot before, and have been mentioning the frequency response parameter. It is true that this parameter is the most important one in the intuitive performance of the speaker, because the audio frequency of the human ear is 20Hz~20000Hz. Therefore, the speaker parameters are naturally hoped to be wider and wider. Well, the speaker in the above example is 80Hz~16000Hz. This parameter is already very good. We all know MP3 format music on a developmental topic. Some people should have heard lossless music, such as WAV, but often we can’t hear it. There is a big gap between the two. Some people may say that your speakers are not good enough and the monitor speakers can hear you. I admit this, but what we all have to admit is that the gap is really limited. But when we observe the size of the two files, we will find that MP3 is basically 1/10 the size of the WAV format. Why is the difference in data volume so large, but the sound quality loss is not serious?


This is the reason for the audio compression encoding. This involves the MP3 algorithm, and the contents inside can be a basket. It is not shown here, but I can say that the MP3 format file will all the signals of the original file higher than 16000Hz. Cut it off, so, think about it, signals higher than 16000 Hz are actually not very serious, are they? Moreover, the loudspeaker parameters only describe the -10dB range. It does not mean that the signal above 16000Hz is gone, but it is relatively small.


Here I have to talk about some engineering-related issues. Sometimes some poor domestic speakers are PK with foreign brands, and it turns out that their frequency range is better. At this time, in this parameter, you need to pay attention to whether both are marked- 3dB or -10dB range.


PS: I am not discriminating against domestic speakers. On the contrary, some domestic speakers are really good, but there are still many false parameters. This should also be related to the way we use parameter cards when doing projects.


Next, let's talk about another important parameter: sensitivity.


The sensitivity of the loudspeaker is the measured sound pressure level of the loudspeaker at a power of 1W and a distance of 1m from the front of the axis. It can also be seen from the literal meaning that this parameter is very important. The higher the sensitivity, the better the loudspeaker, because the lower the power But it can put out a louder voice.


There are two concepts in acoustics. In free space, the distance is doubled, the sound pressure level of the speaker is reduced by 6dB, the power is doubled, and the sound pressure level of the speaker is increased by 3dB. Think about it, suppose the sensitivity of the A speaker is 96dB, and the B speaker is only 93dB , Then if the sound energy of B is to be the same as that of A, its power needs to be doubled. If it is 1W, increasing to 2W does not seem to have much effect, but if A is turning on 500W, then B must be fully driven. 1000W.


The above example also gives us another warning, do not use power to fill the lack of sound pressure level, the best way is to find another speaker with more appropriate sensitivity.


Speaking of the above, the power is pulled out. There are several signs of speaker power, such as peak sound pressure level, maximum sound pressure level, effective sound pressure level, etc. In fact, we usually look at the effective sound pressure level, and this The three are the 3dB relationship:


Effective sound pressure level + 3 = maximum sound pressure level + 3 = peak sound pressure level


In the above example, the peak sound pressure level is 6dB higher than the maximum long-term sound pressure level (effective sound pressure level);


Next, it’s time to talk about the power parameters. The power parameters are the most important thing to pay attention to in the engineering design of the loudspeaker, because this is directly related to the safety of the system, mainly the matching problem with the power amplifier.


In professional speakers, the corresponding power must be marked with 8Ω, or 4Ω, 2Ω, etc., some of which will appear 6Ω, of course, this is a minority, and professional power amplifiers also have corresponding impedance parameters, such as 1000W 8Ω.


In the matching principle, it is often selected between 1.2~2.5 times. For example, if the power of speaker A is 200W 8Ω, then the power amplifier should be between 1.2~2.5 times of it, such as 400W 8Ω; Use-related, if it is a theater and other music venues that require sufficient dynamics, it is best to choose a larger one, such as 2 times or 2.5 times. For some small places, such as meeting rooms, you can choose 1.2 times or 1.5 times.


Here are some other things. If the power amplifier is too large, for example, the speaker is 200W, and the power amplifier is 2000W, you may turn the power amplifier switch knob slightly, and the speaker has directly exploded. In severe cases, the unit may be directly burned out. The configuration is too low. For example, the speaker is 400W, and the power amplifier is only 50W. This is the "mavericks pull the cart" in engineering. Maybe your power amplifier knob is screwed to the end, and the speaker performance is still "weak". In severe cases, it may be silent. But at this time, the power amplifier has power output. According to the normal situation, the power of the power amplifier should be converted into the mechanical energy of the speaker cone for consumption. At this time, if the cone does not vibrate, then the power amplifier will completely become the heat energy of the speaker coil. After a period of time, the paper cone coil gets hotter and hotter, and it will burn out. Both the front and back will burn out. It's just the difference between "quick death" and "slow death".


Finally, let’s take a look at the pointing angle parameter of the speaker. This parameter is also an important parameter and the most commonly considered parameter in engineering, because this parameter involves the coverage angle and is also the most important basis parameter for drawing in engineering design. For example, in the example above, the horizontal is 110 degrees and the vertical is 12 degrees. Here, I need to explain that the angle here is a straight line drawn for a 6dB reduction in the axial sound pressure level after a certain angle offset. It does not mean that the angle is exceeded. There will be no sound from the speakers.


Here, there are also some other things, because we all know that the lower the frequency of the speaker, the stronger the diffraction ability, and the wider the pointing angle should be. Then the pointing angle of the speaker will be different for different frequencies. Normally, The speakers all use 1000Hz as the benchmark. At this time, the domestic great gods once again jumped out to take advantage of the loopholes. Their speakers have a wide pointing angle, and the more kind-hearted ones will clearly mark the measurement at 800Hz. There may be no unkindness. Not paying attention, another dug pit jumped in.


Then we pulled some other, horn speakers.


The image of a horn speaker to everyone is that it can only send high-frequency signals. In fact, it is wrong. The horn speaker can also send low-frequency signals, but the lower the low frequency, the longer the horn and the larger the opening. According to theoretical calculations, the length of the horn is 1/4 of the wavelength of the lower limit frequency, that is to say, to send out a 10Hz signal, the horn needs to be about 8.5m long. At this time, the horn opening may be more aggressive than a building. Do you dare to use it?


To talk a little bit more, sometimes, when designing some small meeting rooms, the owner may propose to choose some speakers with a very good lower frequency limit. In order to improve the music performance of the room system, it is not professional and incorrect. , An acoustician once said that the greatest sadness of the universe is that you cannot hear signals with longer wavelengths. Simply put, the longest distance in the room is used as the wavelength, and the frequency is calculated inversely. Below this frequency, it is impossible in the room. For example, if a room is 3.4m long, then a signal below 100Hz cannot be emitted in the room. How can it be heard by you in the room?


Having said that, some basic main parameters have been introduced. Except for these parameters, the speakers naturally have many other parameters, and now with the development of current technology, some strange speakers have also been born, and the corresponding parameters will naturally be different. , But these core parameters will not change much.