What are the principles of speakers, sound technology and acoustics?

Know the speakers
The speaker is basically composed of three parts: speaker, crossover, and cabinet. According to the number of speakers, it is divided into two units and three units. . . .
There is also a type that integrates the tweeter and the woofer, called a coaxial unit, which is one unit from the outside, but in fact it is still a two unit.
As the name implies, the frequency divider divides the frequency band of the audible sound [20-20000Hz] into several frequency bands and sends them to the corresponding speaker units. According to the division of frequency bands, the two-band divided into high and low-frequency bands are called two-way frequency divided into high, medium, and low-frequency bands called three-way frequency, and so on.
The box body is generally made of logs or medium density boards, and is divided into closed boxes according to the box structure [without inverting holes, the air inside the box is insulated from the outside], and inverted boxes [with inverting holes]. There are also some less common box structures: labyrinth type, exponential type, negative resistance type, horn type, etc.
According to the scope of use of speakers, they are divided into: professional boxes [used for sound reinforcement in performances, halls, halls, venues, and halls]
Monitoring box [professional monitoring for various recording agencies] civilian box.
According to the way the speakers are placed, they are divided into bookshelf boxes and floor boxes. The bookshelf boxes are mostly two-unit, two-way structure, and are mostly used in rooms less than 20 square meters. The floor box is mostly multi-unit, multi-frequency structure. Use more than 20 square meters.

The performance index of the speaker:
General speakers are marked with many of his application parameters, the most common ones are:
Power: Generally measured in W or VA, the common one is nominal power [rated power, non-distortion power] refers to the maximum input power under the condition that the nonlinear distortion does not exceed the standard range of the speaker. It is the normal working power of the speaker, and it will not be damaged if it works continuously for a long time.
Sensitivity: His definition is the sound pressure generated at one meter away from the reference point when a pink noise voltage of 1 watt is applied to the speaker. Expressed in decibels [db]. The higher the sensitivity of the speaker, the louder it is under the same driving power, which is very important when using a low-power amplifier.
Impedance: It refers to the pure impedance presented by the speaker when the audio signal is added to the input end of the speaker. The common ones are 4 ohms and 8 ohms, and there are also 3 ohms and 5 ohms systems abroad. Pay attention to match with the output impedance of the power amplifier when using it. Especially the matching of the amplifier to the speaker impedance is particularly important.

Frequency Range:
Its definition is difficult to explain in a few words. Generally, it refers to the frequency reproduction range of the speaker when the high and low ends of the audio range drop by minus 3 db. Naturally, the wider the better, the current HI-FI speakers can achieve 20000HZ or even 30000HZ playback at the high frequency end. It is not a problem to achieve 20HZ due to the limitation of the speaker diameter and the volume of the cabinet in the low frequency range. Not easy, the low frequency range of general bookshelf speakers is even worse.
Okay, now you have some knowledge of speakers. To be honest, it is very simple, but it is extremely difficult to do well. It is not difficult for beginners to make a pair of entry-level HI-FI speakers by themselves after mastering a certain basic speaker knowledge. Especially nowadays, some merchants have launched many speaker kits. As long as you install them carefully according to the production drawings, the success rate is extremely high. And because these kits have been carefully designed and matched by the manufacturer, the sound quality and effect are guaranteed. And its cost is only one-half to one-fourth of the finished product. Compared with the imported speakers with a set of units, the speakers made by the author with the Gentleman Bao’s 8545K unit have been evaluated by many senior enthusiasts. The sound effect is by no means lower than that of foreign products, and the cost is only more than three thousand yuan, only four of the imported ones. One part.
Don't make speakers, buy a few units and frequency dividers, buy a finished cabinet and install it on top. The speakers made in this way are definitely not good. Moreover, there are too many fake and shoddy products on the market, and the quality cannot be guaranteed. The safer way is to mail-order complete sets from some reputable sales units. If you have good woodworking skills, you can build the cabinet yourself according to the recommended drawings, or you can ask a carpenter to do it for you, as long as the cabinet volume matches the recommended volume of the woofer.
Now you can trust yourself, the speakers can do it yourself! It is easier to succeed in making entry-level speakers. You only need to mail-order a set of a certain quality kit, and make a pair of cabinets that meet the requirements of the kit plus a production day, OK!

Next, we will introduce several low-priced, easy-to-make, and excellent speaker kits and spare parts in the next issue. Quickly prepare the silver in your pocket.

 
Sound technology and acoustic principles
Principles of Acoustics

(1) Acoustic history
When a tree fell down in the forest, there was a loud noise, but no one was in the virgin forest, so the sound was not heard. Does this count as a sound coming out? The sound is definitely coming out, because when tree trunks and branches touch the ground, they all produce certain sounds, but no one hears them, but the sounds are heard by humans or other animals. It is different, so this is what is called Psychoacoustics acoustically.
The acoustic principles I talk about here are mainly to enable a tuner to understand all aspects of acoustics, rather than conducting acoustic research, or master’s or doctoral acoustic thesis, so the acoustic theories I’m talking about in this book are all It can actually be used by people who operate audio on site.
In 1915, there was an American named E. S. Pridham put a telephone listener of the time on a horn that played record audio, and when the sound could be heard by a group of people celebrating Christmas in San Francisco, electroacoustics was born. When the First World War ended, at the inauguration of President Harding of the United States, the Bell Company of the United States connected the dynamic receiver of the telephone to the horn of the record player at the time, and the sound was transmitted to watch the inauguration of the president. A large group of people at the ceremony produced a lot of professional sound research and development of the science of sound reinforcement engineering. Audio researchers are not simply trying to improve audio equipment, but also doing various experiments to understand the human response to hearing. However, the most advanced acoustic researchers all understand that acoustics is a holistic study. They have to understand every aspect of audio equipment and the physiological response of humans to hearing. They have made great contributions in the past many years until now. As early as 1877, Lord Raleigh of the United Kingdom had done acoustic research. He once said: "All issues related to sound, whether directly or indirectly, must be decided by our ears, because it It is our auditory organ, and the decision of the ear should be regarded as the final decision, and there is no need to accept appeals. But this does not mean that all audio research is done by ears alone. When we find that the foundation of sound is a When we detect physical phenomena, we have to move to another field of acoustic realm, which is physics. Important fixed rates can be derived from research, and our auditory induction must also accept these fixed rates." We It can be seen from the above paragraph that even when there is no electroacoustics produced, the older generation of scientists thinks that this is the field of physics.

The famous scientist Lord Calvin of the United Kingdom often said: "When you measure what you describe and can express it in numbers, you already have some knowledge about it. But if you can’t express it in numbers, then your knowledge It is still rudimentary and incomplete; for anything, this may be the source of knowledge, but your ideas have not yet reached the realm of science." Lord Calvin (1824-1907) was the best scientist of the 19th century One, in order to commemorate this great man, later scientists named the absolute temperature -273.16 degrees Celsius as 0 degrees Calvin degrees.

Don & Carolyn Davis are the authors of the book "Sound System Engineering". This book is called the Audio Bible, and it is a must-read for almost everyone who studies audio in foreign countries. I quote this paragraph in his book: "Knowledge of mathematics and physics is a necessary condition for a substantial understanding of sound engineering. The deeper the understanding of these two sciences, the more you will be able to overcome the ideas you get from your senses. And to use science to cite facts. The famous acoustician James Moya once said: "In acoustics, anything that is obvious on the surface is usually wrong."

I quoted the advice of several scientists and acousticians above, mainly because most people who do acoustics today are of course very interested in acoustics and music, but they think they can identify what is just by their hearing. Good or bad sound, I don’t understand that this is a professional engineering discipline, and it is not good sound. As far back as the 19th century, Sir Ley Lee pointed out that this is a realm of science, and modern sound engineering is also developing hard like other sciences, so sound engineering is inseparable from mathematics and physics.

(2) The difference between live sound and studio sound
There are many differences between the live audio operation explained here and the recording technology. Many people think that the highest level of audio is the recording technology, which is not comprehensive. In terms of recording technology, there is basically no feedback, because when operating in a recording room, all the peripheral factors can be controlled, but when the live audio is replayed, we cannot avoid many live audio problems. , So live sound and recording sound are two different kinds of knowledge.
The requirements for live sound and studio sound are different, so there are many different equipment. For example, the mixers used in the recording studio have multiple parameter equalization for each input, so that the sound engineer can fine-tune each input source as much as possible to achieve the best source effect. A mixer used for live sound usually has simple equalization for each input. Because in many cases, the live tuner does not have much time to fine-tune the sound source of each channel carefully. In the live audio mixer, the volume control faders of each channel can not only attenuate the volume, but also Can gain 10-14 dB. If you are a mixing console used in a recording studio, this fader often does not need to be used for gain, so the English name of this fader is fader, which means attenuator. High-power amplifiers used in live audio, they will all have fans for heat dissipation, because live audio amplifiers often work at the maximum power output, and there are many times when the live audio is outdoors, the surrounding temperature may be quite high. If you are in a recording room, there is usually an air conditioner. Of course, the temperature will not be too high. The power amplifier in the recording room is mainly used to push the monitor speakers. Of course, it does not need to output a lot of power, so the power amplifier only needs to be ordinary The radiator can dissipate a small amount of heat. If the power amplifier is equipped with a fan, the sound from the fan will cause noise. Therefore, the power amplifier in the recording room basically does not need a fan.
The speakers used in live sound are designed to spread large sound pressure to distant audiences, so they need to be very efficient, but the monitor speakers used in the recording room are used by the sound engineer to monitor the sound source or The final result of the recording is that the sound engineer is sitting very close to the monitor speaker to monitor, so the monitor speaker is a near-field speaker that does not require high sensitivity, and its function is completely different from that of a live audio speaker.

(3) The relationship between audio frequency and wavelength
Many on-site tuners ignore the relationship between audio frequency and wavelength. In fact, this is very important: audio frequency and wavelength are directly related to the speed of sound. Under altitude air pressure and 21 degrees Celsius, the speed of sound is 344m/s, and I contacted domestic tuner, their common sound speed is 34Om/s, this is the speed of sound at a temperature of 15 degrees Celsius, but The main thing everyone remembers is that the speed of sound will change with air temperature and air pressure. The lower the temperature, the higher the density of molecules in the air, so the speed of sound will decrease. Sound, because the air pressure decreases, the molecules in the air become sparse, and the speed of sound increases. The relationship between audio frequency and wavelength and sound is: wavelength=sound speed/frequency; λ=v/f, if the speed of sound is assumed to be 344 m/s, the wavelength of 100Hz audio frequency is 3.44 m, 1000hz (that is, lkHz) wavelength That is 34.4 cm, and a 20kHz audio wavelength is 1.7 cm.

(4) High, medium and low frequency of the speaker
For example, we now have a paper cone speaker unit at 18 o'clock, installed in a speaker made of wood, and the panel area of this speaker is 1 square meter, that is, the height and width of the panel are both 1 meter. How do we calculate the high, medium, and low frequencies of this speaker? First, we have to calculate the diagonal length of the speaker panel, which is the square root of 2 = 1.414m. When the 1/4 wavelength of any frequency exceeds 1.414m, For this speaker, it is a low frequency; if the 1/4 wavelength of a frequency is 1.414m, the wavelength is 4×1.414m=5.665m, this frequency=344m/s÷5.656m=60.8/ s=60.8Hz, so any audio frequency below 60.8Hz is its low frequency for this speaker. When the frequency of 60.8 Hz or lower is transmitted from the speaker, their diffusion image is spherical, which is equivalent to that if we hang the speaker in the middle of a room, the volume of these frequencies is at the front, back, left, and right, and up and down of the speaker. The sound pressures emitted are all the same, and the emitted sound becomes non-directional. When the 1/4 wavelength of a frequency is less than the diagonal length of the speaker panel, but this wavelength is greater than the radius of the speaker, this section of frequency is the mid-frequency of the speaker. For example, we are now using a 18 o'clock unit. The radius of this unit is 9 inches, which is 22.86cm=0.2286m. The audio frequency is 344m/s÷0.2286m=1505Hz. The frequency from 60.8Hz-1505HZ is the mid-frequency of this speaker. . The shape of the mid-frequency diffused from this speaker is hemispherical, that is, if we release this frequency from the speaker just suspended in the center of the room, the shape of the sound diffused from the speaker panel is hemispherical. The sound of this frequency cannot be heard behind the speaker. The frequency of 1505Hz and higher is its high frequency for this speaker. The shape of the high-frequency sound diffused from the speaker is cone-shaped. The higher the frequency, the narrower the cone shape. Generally, if the frequency exceeds 4 times of the initial high frequency, the shape of the sound diffusion will gradually become a straight line without diffusion. If you are not sitting in the position of the alignment unit, you will not be able to hear these high frequencies. Therefore, if many high-frequency units are cone-shaped, the diameter of the cone is very small. Try to increase the lower limit of the high frequency of the speaker as much as possible, hoping to increase the width of the high-frequency diffusion. We often see tweeters in home audio speakers, usually l-2 o'clock paper cone units, or hemispherical units, for this reason. As for the tweeter of professional live audio, because it has to emit a lot of high-frequency sound pressure, it must be treated with horns.

(5) Various sound fields

When a cone speaker receives the signal from the amplifier, the cone will

Shake back and forth. When the paper cone advances forward, the paper cone hits the air molecules in front of it. The air in front of the paper cone will increase the pressure, and these molecules will continue to move forward and collide with the air molecules in front of them. Cause a slight high air pressure. When the paper cone retreats, the air molecules in front of the paper cone will create a slight vacuum, and then these molecules will follow the paper cone back, causing the air here to have a slight pressure reduction. But we must not forget that the air is elastic, but the air in front of the paper cone is just shaken by the motion of the paper cone, and cannot reach the elasticity of the air itself. At this time, we have to look at the wavelength of this frequency, and the sound will go until it leaves. When the distance of the paper cone is 2.5 times the wavelength, the air exerts the elastic force that causes the sound. For example, for a frequency of 100 Hz, its wavelength is 3.44 meters, so the sound must leave the paper cone 2.5 x 3.44 meters = 8.6 meters to be the real 100 Hz sound. If you use 100 Hz to calculate, the distance from the paper cone is less than 8.6 meters before the near sound field of 100 Hz, and more than 8.6 meters is the far sound field of 100 Hz. Why do we need to understand the near and far sound fields? Many times an electric bass player in a band does not understand the effects of the near sound field. On his electric bass speakers, there is an equalization knob that says Bass is the title of this musician. The electric bass player usually stands not far away from the electric bass speaker to perform performances. If he is standing near the sound field and sometimes feels that the bass is insufficient, he will increase the Bass equalization knob as much as possible, but the audience is in Their position will hear very strong bass, which often causes bad effects. These strong bass will also run into the singer’s microphone. If the tuner feels that the singer’s voice is not enough, he will raise the singer’s voice, but at the same time raise the low volume of the electric bass. The sound ran into difficulties. The lowest E string of electric bass is 41Hz, but because the pickup is placed at the end of the string, the first harmonic of 41hz, 82Hz, is the main electric bass low frequency. The wavelength of 82Hz is 4.2 meters (344m/s). Divide by 82/s=4.195m), so the far sound field of 82Hz is about 10 meters away from the electric bass speaker, and because the electric bass player will not stand so far away from his speaker, The sound he hears is only the near sound field, not the sound that the audience hears. So when we talk about the far and near sound fields of the speakers, we mainly pay attention to the frequency and its wavelength, rather than simply looking at how far away from the speakers is equal to the far or near sound field. The most important thing is to remember that when we enjoy music, To be in the far sound field, not in the near sound field.

(6) Direct sound field, reflected sound field, and indirect sound field
When the speaker emits sound in a room, the listener can hear the sound transmitted directly from the speaker, this is the indirect field (indirectfield), but it can also hear the sound reflected from the wall, ceiling and floor, which is called Reverberant field. The more the listener hears the sound of the direct sound field, the smaller the sound of the reflected sound field, the better the sound, because the sound of the direct sound field can be controlled, but the sound of the reflected sound field cannot be controlled. It will add noise to the sound from the direct nursery, reducing the original sound clarity, so listeners who sit closer to the speakers will feel a better sound effect, while listeners sitting behind are likely It is because the reflected sound field they hear is louder than the direct sound field, the sound effect will be worse and the clarity will be reduced. Sometimes when a band is performing on stage, because they do not have monitor speakers, and the main speakers on both sides are placed close to the stage, the sound that the band and singer hear is not emitted from the direct sound field at all. The standing position is called an indirect sound field. Of course, the sound effect will not be good. This will also affect the performance level of the band and make the audience hear the bad performance sound.

(7) Interface interference
When we choose the location of the speaker, it is important to note that the sound from the speaker will be affected by the interface next to it and cause interference. For example, if the main speakers placed on both sides of the platform, their bass cones are about 1 meter away from the ground and the walls next to them, a 4-meter-wavelength audio will be interfered by these two interfaces. The frequency of a 4m wavelength is 86Hz (344m/s ÷ 4m = 86Hz). When the 86HZ sound is released from the speaker, the large air pressure just hits the ground and the wall within 1/4 of a week, and then 1/4 Zhou reflected back to the paper cone of the speaker, but at this time it happened that the paper cone was going to retreat. The large air pressure reflected from the ground and the wall would be offset by the retreating action of the paper cone, resulting in the loss of very important bass. If you encounter this situation, you should move the speaker back 0.5-1 meter to the stage so that the sound from the speaker cannot directly hit the ground. If you can move the speaker to the walls on both sides, you can use the wall. The reflection system makes a louder volume. The frequency of 80-100Hz is very important. It is the resonance point of our lung space and the resonance frequency of the bass drum. If the speaker is placed in the wrong position because of the lack of understanding of the interface interference, it is really not worth it. .

(8) High and bass effects
It is difficult for us to specify a frequency above a certain frequency as treble or below a certain frequency as bass. We often say that human hearing is from 20Hh-20KHz, but the frequency of 20kHz is rarely heard by people, usually only young people under 20 years old. , Their ears can only be heard without any damage. If you do a hearing test, the highest listening frequency is only 8 kHz. When the sound is transmitted, the high frequency decays much faster than the low frequency. If 1kHz is compared with 10kHz, when the sound runs 100 meters, the frequency of 10kHz will be attenuated by 30-35dB compared with the volume of IkHz. (Please refer to Figure ①) Compared with low frequency, high frequency sound is more directional. After the high-frequency sound ran out of the unit, if it is blocked by an object, the high-frequency sound can no longer pass through. This is very different from the low-frequency sound, because the high-frequency sound has a shorter wavelength and will not be blocked by an object. Turning, but the low-frequency wavelength is relatively long, so in many cases, even if there is an object blocking in front, the low-frequency can also be turned. For example, some professional speakers are designed to put a high-pitched horn in front of its woofer, but for the low frequencies emitted by the woofer, it can't see that something is blocking the sound in front of it, so the low frequency It can still be passed on. From our hearing point of view, we need to hear high-frequency sounds to distinguish all kinds of different sounds, but if it is only talking about human conversation, we only need to hear frequencies of 4kHz and below to be able to distinguish immediately Who is talking. For example, the voice transmission of the telephone, the high frequency only reaches 4kHz, so sometimes when a person has not talked to you for a long time, when he calls you, just say: "Hey!", you can immediately identify him. The voice of a friend you haven't talked to for a long time. We listen to high frequencies also have directionality, that is, we can distinguish the direction of the source of high frequency sounds. Because the high-frequency sounds have a slight time difference when they reach our two ears, they have different phase changes when they come to the ears. We can identify them by the changed phase?

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