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Why are there so many kinds of microphones? What kind of microphone is better?

2021-02-09 551
Why are there so many kinds of microphones? What kind of microphone is better? This is one of the most frequently asked questions by students in my audio class.
First of all, there is no microphone in this world that can be suitable for all tasks and all scenarios. This may be a better answer to the question "Why are there so many kinds of microphones on the market".

Our ears are very sophisticated and complex sensors that can convert sound signals into electrical impulses, and after they are transmitted to the brain, our brains can interpret them as "sounds".

The unit of sound frequency is Hertz (Hz), and 1 Hz represents the number of times per second when a sound wave passes through a certain point (that is, the number of times a complete vibration process is completed per second). Our ears can convert 20Hz-20kHz sound signals.

Unlike our ears, microphones can only accurately convert (and reproduce) sound signals within a specific range, which is usually smaller than 20-20kHz.

Why are there so many kinds of microphones? What kind of microphone is better?

Frequency response icons of several different microphones
If the microphone can be within a certain range without increasing or decreasing the volume reproduction frequency, we call this frequency response range "flat". When measuring microphones, this item is called "frequency response". For an engineer, this is a characteristic that must be known when selecting a microphone for a specific use scenario.

The frequency response of the microphone will have a certain impact on the sound quality, because the microphone usually cannot reproduce all the frequencies present in the audio signal well.

When choosing a microphone, another characteristic that needs to be understood is the signal-to-noise ratio (S/N), which represents the useful audio volume (S) from musical instruments and singers, and the noise floor (N) of the microphone itself. ratio. (Any analog and digital audio equipment will have a signal-to-noise ratio and dynamic range, and the dynamic range is the sum of the signal-to-noise ratio and headroom).

Why are there so many kinds of microphones? What kind of microphone is better?

However, when choosing a microphone, the most important consideration is often its design type. There are two basic types of microphones: dynamic microphones and condenser microphones.

Although generally speaking, dynamic microphones have always been the preferred choice of live sound reinforcement engineers, condenser microphones are gradually entering the stage of live sound reinforcement. As for this reason, we will explain later.

Moving coil magnetism

Strictly speaking, dynamic microphones can be divided into two types: one is a general dynamic microphone, and the other is a ribbon microphone. The working principle of dynamic microphones is electromagnetic induction. I believe you have all touched magnets. They have two poles, one of which is the "North Pole (N)" and the other is the South Pole (S).

Sectional view of dynamic microphone and condenser microphone

When two magnets with the same pole are close to each other, they tend to repel each other, and when two different poles are close, they tend to attract each other. And if the magnet is kept close enough to each other, it will generate attractive force, but can not touch, it will generate a magnetic field before the two.

And in this magnetic field, there are "magnetic lines of induction" invisible to the naked eye. In the internal structure of any dynamic microphone, there are various magnetic fields. In the ribbon microphone, it is a thin metal strip suspended in the middle of the magnet. When the vibration of the sound wave drives the aluminum strip to vibrate, it will also vibrate. This kind of vibration cuts the magnetic lines of induction and generates voltage. The voltage is conducted through the aluminum strip and is directly affected by the vibration frequency of the sound wave.

In general dynamic microphones, a thin film (ie, diaphragm) is connected to the coil. The vibration of sound also causes the diaphragm/coil to move in the magnetic field, cutting the magnetic lines of induction and generating an induced voltage in the coil. Likewise, the vibration frequency is the same as the sound frequency.

Generally speaking, the sensitivity of a dynamic microphone depends on the size of the diaphragm, the gravitational strength of the magnet, and the number of coil turns.

Although ribbon microphones are more sensitive than dynamic microphones, they are also more fragile. In addition, ribbon microphones have a two-way pickup mode-because they are equally sensitive to sounds in front of and behind the microphone. Taking into account this two-way sound pickup mode and its own fragility, generally speaking, everyone thinks that this kind of microphone is not suitable for live stage sound reinforcement.

Easy to move dynamic microphone

The general dynamic microphones are just the opposite, they are very sturdy and durable. This feature makes dynamic microphones an overwhelming advantage for bands or live sound reinforcement personnel. And the general price will be cheaper.

Most dynamic microphones are unidirectional-they can only pick up the sound from the front. This is an advantage, because for live sound reinforcement, if the sound from the monitor speaker enters the microphone again, it will produce an acoustic feedback phenomenon called "howling", which is a problem that must be avoided for live sound reinforcement . Every live sound reinforcement engineer will try his best to avoid the problem of acoustic feedback. After all, if a whistling occurs, every audience present knows that this cauldron must be memorized by the sound reinforcement engineer.

Similarly, the gravitational strength of the magnet, the number of turns of the coil, and the size of the diaphragm are equally important. Large-diaphragm dynamic microphones are usually more sensitive than small-diaphragm dynamic microphones. When recording drums, large diaphragms are usually used, except for snare drums. Therefore, snare drums usually emit a high-frequency extra sound. In this case, small diaphragm microphones such as SM57 will be better. .

AKG D 112 (left) is more suitable for kick drum, while Sennheiser E604 is suitable for tom drum, and it is more convenient to install

In addition, because the snare drum also produces a higher sound pressure level, this will also cause certain damage and distortion to the large diaphragm microphone.

Some large diaphragm microphones, such as AKG D112, D550 or Shure Beta 52, are very suitable for use on the kick drum. And Sennheiser also has many microphones suitable for recording drums, such as E602 (suitable for recording kick drums) and E604 (suitable for drum recording).

The E604 also comes with a stand that can clamp the rim of the drum, which saves the need for a bulky microphone stand and makes the stage cleaner and more concise. (I even used it in the recording studio.)

If you are accustomed to using the front wedge speaker as a stage back to listen, dynamic microphones are undoubtedly a good choice. They can increase the gain enough, but will effectively avoid the occurrence of acoustic feedback.

And if you are using an in-ear hearing system, you can try to use a condenser microphone to pick up human voices or musical instruments. Although you may increase your budget, you will get a correspondingly better sound quality.

Use condenser microphones on stage

Now, condenser microphones are increasingly used on the stage of live sound reinforcement. Condenser microphones are very sensitive and have a very flat frequency response in the 20Hz-20kHz range. Part of the reason for this phenomenon is their design.

The working principle of a condenser microphone is a variable capacitor, a fixed plate and a movable plate. The function of these plates is similar to a polarized magnetic source. The sound vibration drives the movable plate of the microphone to vibrate, and the vibration frequency is also the same as the sound frequency.

As the movable plate vibrates, the distance between the two plates is constantly changing, and their function is the electronic components in the capacitor. The change of the distance between the plates will cause the change of the capacitance, and then through the small electronic circuit in the microphone, the current of the analog sound signal is generated. Dynamic microphones are usually charged by manufacturers when they are made, so they can maintain a voltage of 20% for a long time.

Unlike dynamic microphones, condenser microphones do not have permanent charging magnets when they are made. So every time they are used, phantom power must be used to power their diaphragms. This kind of power is generally transmitted through a microphone cable. The phantom power supply is usually a 48V DC power supply, which can meet the needs of large-diaphragm condenser microphones.

The variable capacitor design of the capacitor microphone makes it particularly sensitive to changes in sound pressure. They are also very "hot" microphones. Guitarists usually like to use them in conjunction with active circuits in guitar pickups because of their excellent sensitivity.

Generally speaking, the frequency response of condenser microphones is relatively flat. There is a more detailed classification under this category, called electret condenser microphone. This design can use a smaller DC battery or phantom power supply, and the voltage is much lower than the 48V required by a general condenser microphone. But please note that the battery here and the battery required by the wireless system in the wireless microphone should not be confused.

Around the mid-1960s, the legend of the EV, Lou Burroughs, publicly demonstrated what happens when an open microphone is placed directly on the speaker horn.

About phantom power

Phantom power not only provides the necessary voltage for the circuit board, but also provides power for the on-board impedance transformer. Without phantom power, condenser microphones cannot work at all. So, where does this phantom power come from? Generally speaking, the mixer will have its own phantom power supply.

Many mixers have separate buttons or switches on each channel to enable or disable phantom power. Some mixers have a switch that can control multiple channels. Only this one switch can turn on or off the phantom power of all channels.

Fewer buttons undoubtedly save costs, but relatively sacrifice some functions. Some consoles do not provide phantom power at all, or only provide 18V phantom power for electret condenser microphones, so sometimes an external 48V phantom power supply is needed to power condenser microphones.

Why are there so many kinds of microphones? What kind of microphone is better?

In some mixers, the phantom power can be turned on or off on each channel separately, such as Allen & Heath GL4000 (left). Other small mixers, such as Mackie 406M, use a switch to control the phantom power of all channels.

Because condenser microphones sound crisp and clean, many people like to use condenser microphones when recording human voices. And there are many models designed specifically for recording human voices. But there is one thing to note, because condenser microphones are more fragile than ordinary dynamic microphones, so when using them on a tour, it is better to prepare a strong shockproof box for them.

Also note that because capacitors are very sensitive, acoustic feedback is more likely to occur. When using condenser microphones in sound reinforcement, you need to pay special attention to managing the volume of the stage. In this case, it is necessary to use in-ear monitors. In addition, you need to inform the singers so that they can take corresponding measures.

So, what about using phantom power when using a dynamic microphone? Phantom power will not cause damage to dynamic microphones, but it is not necessary to use phantom power for dynamic microphones. But remember, when using a condenser microphone, you must turn on the phantom power supply! (Because if you don't turn it on, the microphone won't make a sound at all.) Also, before turning on the phantom power, remember to mute the track first, otherwise some noise may be generated.

There should never be too many microphones to choose from. Inventors and engineers are also constantly trying new technologies. Continue to experiment and continue to summarize, I believe this will make your live sound reinforcement sound better.
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