[Hardware] What is the impedance of a microphone and why you should care

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As a general rule, when you have a microphone built into the headphones, you don't pay much attention to its specifications in favor of the quality of the audio that you are going to perceive; However, when you want a microphone to make quality recordings or to stream, then you will not only look for a dedicated one but you will have to take into account many of its specifications. Among these characteristics, impedance usually stands out, but do you know what it is and how it influences the quality of the sound? Next we will tell you about it in great detail.

We have already addressed issues related to microphones before, such as the different types of design or the fundamental differences between dynamic and condenser ones, since they are generally the fundamental criteria that must be taken into account before choosing the model that best suits you according to the purpose. you want to give it. When we enter the impedance of the microphone we are, to put it in some way, spinning fine, since as we will see below, despite not being a too influential factor, it can make a lot of difference in the final result. We are going to get into the matter, and how can it be otherwise we have to do it from the beginning.

What is impedance in a microphone
The literal definition of impedance tells us that it is "a measure of the opposition / resistance to alternating current in a circuit when voltage is applied to it." Impedance is measured in ohms, just like resistance, and in fact this term is often referred to as the "AC resistance" of a circuit.

Microphone impedance

However, when we transfer the impedance to the audio niche and more specifically that of the microphones, we could say that it is applied in a somewhat different way:

Audio signals are AC (alternating current) voltages since they have negative and positive voltages (the positive and negative amplitude of the signal). Audio signals are therefore alternating currents that have a positive part and a negative part.
The impedance of a microphone controls the flow of alternating current in an audio circuit when a voltage is applied to the signal.
All microphones, like any electronic device that generates AC voltage, has an output impedance.
A microphone creates a circuit with the preamp (or other audio circuit) to which it is connected. This device has an input impedance known as the microphone load impedance.
The microphone output impedance must be a fraction of the preamp input impedance for the circuit to work.
In short, impedance is the resistance of alternating current. The higher the impedance of a microphone, the more prone to interference and signal loss in the cable. Also, depending on the input of the preamp, a couple more decibels of volume can be lost in the mixer, and if the impedance of the mic is as high as the input of the preamp, up to 6 dB is lost in the most extreme case. .

Today's most common microphones are all low impedance, with values between 50 and 600 ohms. Most mic preamps have input impedances around 2000 ohms, so taking all of this into account, the mic's impedance will always be lower than that of the preamp, so signal losses are theoretically minimal. in any case.

What should you keep in mind when it comes to impedance?
In the specification sheet of any microphone you will find its impedance value. Any professional mic is considered "low impedance," which means its range is roughly 50 to 600 ohms, although it is true that you will rarely see a professional mic with more than 250 ohms. The general impedance ranges are as follows:

Low impedance microphones: <600 Ω
Medium impedance microphones: 600 Ω - 10,000 Ω
High impedance microphones:> 10,000 Ω
Neumann microphone

As we have mentioned before, when choosing a microphone you should first be clear if you are going to use a preamplifier, or otherwise if you intend to use it on a PC without a previous one, what is the impedance of the microphone input of your card. sound. Unfortunately, most motherboard manufacturers do not specify these parameters, but if they tell you which chip they mount, you can search for it on the Internet, and even if you cannot find the specific parameter, you can find compatibility tables.

For example, on an MSI Z370 Gaming M5 motherboard it does not say what the impedance is but it does use a Realtek ALC1220 chip, and looking for information on this indicates that it has impedance detection and that it is compatible with microphones up to 600 ohms of impedance, which means that most likely the preamp on this chip is precisely 600 ohms.