Speaking of the number one weapon in the hands of sound engineers, it is none other than the recording microphone. The importance of the recording microphone is that it is at the forefront of the recording equipment. Its quality determines the overall quality of your recording. The sound recorded by a poor microphone cannot be improved even if it is repaired later. Therefore, proficiency in the microphone has become an essential skill for recording engineers. Recording should occupy at least 70% of the importance of the entire music production process. In the recording, the microphone should also have a proportion of more than 70%. Many times, what is done in the later stage is just to make up for the lack of microphones or improper use of the microphone in the early stage recording. If we can do well in the recording and use the microphone well, then we can be more relaxed in the later stage.
The sound engineer’s knowledge of recording microphones should be the same as a soldier’s knowledge of his own gun. Below, we will start with the structure of the recording microphone and analyze the principles and characteristics of the microphone.
Directivity of recording microphone
All microphones have a place to receive sound signals. Here we call it the sound head. The general position is behind the diaphragm. The sound head has three structures. One is the single-sided pressure receiving type, with only one end open, so that only one side of the diaphragm can receive sound pressure. The other is pressure angle acceptance? Fully open, that is, both sides of the diaphragm can accept sounds from various angles. The last type of pressure angle acceptance? Semi-open type, is that both sides of the diaphragm can only receive sound waves in a specific direction. The specific principle will be described in detail later.
There is only one side of the diaphragm that can receive sound pressure, and the sound waves on the back will go around to the front, so it can also be sensed. In this way, sounds in any direction can be picked up, so we call this directivity as omnidirectional , It is usually called Omni in English, or it is replaced by a circle pattern.
Both sides can accept the diaphragm of various sounds, and the sound waves from both sides go around to the front and the back respectively, thereby generating the same pressure, which is canceled out, and the result is a figure of eight, which is what we often say Figure 8 points.
There is one last case. In this case, the back sound waves are allowed to pass through the diaphragm, so that the sound waves going to the front will cancel each other out. Therefore, in this case, the rear sound cannot be picked up. This is the heart. Type pointing microphone. Generally, a heart pattern is used instead.
At this time, someone was yelling. There are only these three kinds of directions, right? How did I see that there are 7 kinds of directions, and how did that come out? There are also some microphones that have these directions, how do they do it? The answer to this question seems to be very simple, that is, head changing or superposition of points. Changing the head is very simple. Unscrew the original sound head and replace it with a suitable one. Blue's large-diaphragm microphones prefer this technology, so they can often be seen. Superposition is to superimpose two kinds of pointing heads together to become a new pointing. For example, a cardioid pointing and a figure 8 pointing are omnidirectional. Many large diaphragm microphones with options are implemented in this way.
The sound head not only determines the direction, but also determines the characteristics of the tone. The single-sided pressure-receptive sound head can pick up natural and clear sound, with excellent depth and realism, and low frequency control is also very good. The pressure angle-receptive capsule will have a close-talking effect. If used properly, it is a very good low-frequency EQ, which can control the frequency response very naturally, but the effect will be bad if it is not used well.
Recording microphone, earphones and speakers
Everyone will ask when you see this title, are these three related? The microphone is for recording, while the earphones and speakers are for replaying sound. It seems to be the opposite, completely untouched. But if we analyze their principles carefully, we will find the similarities. Both the earphone and the speaker convert the digital signal into the vibration of the diaphragm to produce sound, while the microphone converts the vibration of the diaphragm into a digital signal. The difference between the two is just the opposite of the signal flow, which shows that the characteristics of the two will partly overlap. Having said so much about the relationship between the three, the main purpose is to compare it with headphones or speakers in the future, so that you can have a deeper understanding of certain characteristics.
Principles and characteristics of dynamic microphones
First of all, we recall the principle of dynamic speakers.
When the audio current flows through the moving coil, according to the principle of magnetoelectric induction, the moving coil will drive the paper cone of the speaker to move back and forth, and the speaker will restore the electrical signal to sound. As you can see, according to the principle of magnetoelectric induction in physics, this process is reversible. The dynamic microphone is exactly this reversible process. The dynamic microphone, that is, the diaphragm receives the pressure of the sound wave, and drives the coil to move in the magnetic field, thereby generating electric current. This is how dynamic microphones work. At this time, someone asked, so why haven’t you seen anyone use a dynamic speaker as a microphone? The reason for this is that the impedance of the dynamic speaker is very small, and the amplifier at the back of the microphone requires a high-impedance input. In this way, this seemingly beautiful marriage can only end with a divorce.
Speaking of the advantages of dynamic microphones, one of the biggest advantages is that they are not afraid of falling. Many singers like to bounce around when singing live, so the microphone becomes a bigger victim. Sometimes a microphone may even drop from the sky. If that microphone happened to be your U87, I guess you had a heart of death at the time (but don’t forget to write in your will that the property beneficiary is me) . Widely used.
Another "immortal Xiaoqiang" ability of dynamic microphones lies in the ability to withstand great sound pressure. The sound pressure that a dynamic microphone can withstand is 10-20dB higher than that of a condenser microphone. And this makes the dynamic microphone can be used in the scene, because there are many unexpected situations in the scene, the sound pressure changes are sudden and unpredictable, and the greater sound pressure endurance of the dynamic microphone makes it better. Cope with this situation.
A lot of the advantages of dynamic microphones have been mentioned above, but the disadvantages of dynamic microphones must be mentioned below. In principle, the diaphragm of the dynamic microphone receives the pressure of the sound wave and starts to vibrate. This has a response time, which is usually called Attack, the starting time. When the sound stops, it takes a while for the microphone diaphragm to return to a static state. This is usually called Release, the release time. It seems that there is no big problem here, but for the sound quality, it is a kind of distortion.
Another distortion of the dynamic microphone comes from the split vibration of the diaphragm. Due to the physical properties of the diaphragm, it may occur that when sound acts on the diaphragm from a certain angle, the non-uniform physical properties of the diaphragm will cause deformation, which will cause frequency distortion. This is very common in dynamic microphones, causing the distortion of dynamic microphones to be larger than that of condenser microphones.
The sensitivity of dynamic microphones is also relatively low, because the voltage generated by the coil in the magnetic field is too weak. The voltage generated by a condenser microphone is several times that of a dynamic microphone. Therefore, for some extremely small sounds, the dynamic microphone cannot successfully pick up, so it is rough, and in technical terms it is relatively low sensitivity.
So we can summarize the advantages and disadvantages of dynamic microphones. Dynamic microphones have the advantages of sturdiness and strong tolerance, but the disadvantages are that they will cause relatively large distortion and low sensitivity. The sound of a dynamic microphone is not suitable for recording special sounds that require delicate sound. But for a sudden, loud-sound instrument like the drum, it is a magical instrument.
Principles and characteristics of condenser microphones
For high-quality microphones, there must be a sentence in the promotional text, called condenser microphones. The implication is that capacitors represent high-quality goods. And when you look at the price, it is also very high-quality, some of which are still 5 digits. So, what are the benefits of condenser microphones? First of all, let's start with the structure of the condenser microphone. The condenser microphone, as the name suggests, is that the sound head is a capacitor. Readers who have studied physics know that a capacitor is divided into two levels. On a condenser microphone, one pole of the capacitor is the diaphragm, and the other pole is the back plate. The poles are separated by a certain distance. When sound waves act on the diaphragm and exert a pressure, the diaphragm will move. In this way, the distance between the two poles will change, and the voltage will change. Pass this voltage change to the back-end amplifier, and then the signal can be output.
The diaphragm of a condenser microphone is generally a metal film. Someone asked here, can it be made of metal? I replied, if it is an insulator, is it still called a capacitor? It should be noted that this metal film is so thin that it cannot be produced by a factory with a normal process. It needs to be less than 10 microns thick, and the distance between the two poles is only a maximum of 50 microns. Note that the unit here is micrometers, which is almost invisible to the naked eye. This feature directly determines the cost of condenser microphones and their fragile characteristics. Because the requirements are so strict, the production process of condenser microphones is very demanding. There is an electret on the market, which has a certain internal bias, so the process requirements are not as high as the capacitor requirements, and the distance between the plates can be larger, but the sound quality is not as good as a real condenser microphone. At present, some illegal vendors use electrets to expose charging capacity, so be careful.
Condenser microphones are divided into large and small diaphragms according to the size of the diaphragm. This kicked off the prelude to the struggle between the highly qualified large-seismic membrane and the small-seismic membrane. Generally speaking, the diaphragm with a diameter of more than 1 inch is called a large diaphragm, and the diaphragm with a smaller diameter is called a small diaphragm. But it is not a particularly deadly rule. For example, what is the name of a diaphragm with a diameter of 0.9999 inches? It should be considered a big earthquake film.
The characteristics of a large diaphragm are very similar to those of a speaker. Everyone knows that the caliber of the woofer is generally very large, while the tweeter is relatively small. This is because when high-frequency sound waves reach the surface of the diaphragm, the diaphragm will produce corresponding high-frequency motion. If the material of the diaphragm is uneven, the mechanical properties will not be the same. At this time, the diaphragm will have several different vibration conditions, resulting in deformation of the diaphragm. In this way, distortion is inevitable. The small diaphragm is relatively small, so the chance of uneven material is much smaller than that of the large diaphragm. The strength of the entire diaphragm is not easy to deform, so the high-frequency distortion will be relatively small. In the same way, a large diaphragm will not perform as well as a small diaphragm at high frequencies, because the upper frequency limit of the diaphragm is limited. The small diaphragm is good for high frequencies, but not good at low frequencies, because the lower limit of the frequency of the small diaphragm is limited. In this way, the different sound characteristics of the large earthquake diaphragm and the small earthquake diaphragm are cast.
The sound of the big shock membrane is usually warm and generous, and the mid and low frequencies feel very good, very real! The small diaphragm has an amazing resolution at high frequencies and is very delicate. In this way, the overall tone is colder. Therefore, in many cases, the choice of timbre becomes very important.
What is a tube microphone
The condenser microphone is converted into a signal after the sound head, and then there is an amplifier part to increase the voltage and reduce the resistance of the signal. This amplifier can be a transistor or a tube. Since transistors are cheap, enthusiasts look down on them, and professionals don't care, so there is no transistor microphone. The tube, which is born noble and good for life, can be called a tube microphone by itself. It can also fool the public and make them think that they are not among the condenser microphones. The tube microphone is also known as the tube microphone. But in fact, everyone should understand that Guan Zimai is essentially a condenser microphone.