The technical specifications are very similar to electrical elements, do not panic if you do not understand one, here I will try to put it in simple words.
Juan Tamayo *
As sound professionals we have always been taught the learning of certain techniques and technologies, how to program a processor, how to calculate the gain structure, how to align the sound system, among many concepts. Generally in the audio courses there is little talk of microphones, even when you see designs or technical documents they speak of certain brands and usually of the same microphones.
It is as if nothing else existed and the universe of capture was limited. I hope to be able to deliver in this series of articles the basic technical knowledge necessary to understand the specifications of the microphones, how to make technical decisions for the selection of microphones and I hope to be able to deliver design recommendations for your project. Remember that the microphone is the transducer through which the mechanical signal enters and is transformed into an electrical signal. What goes well, it is possible that it goes well, but if it goes wrong it is very difficult for it to sound good.
This article or series of articles are basic knowledge, it is not a design course. The recommendation is to look for bibliography or attend technical courses that will help increase knowledge. I hope I can achieve interest in studying about microphones and that they can apply the right microphone in the right place.
How to read the data sheet of a microphone?
When I started in the audio world, I have to admit, I did not know much about microphones. I thought it changed little from one to another. Or great surprise when I enter Audio-Technica and I know a whole universe of audio signal capture solutions, but I did not find how to explain the differences between them. So we started with the support of engineers a technical course on microphones. In this article I hope to deliver a summary of the course.
My goal is for you readers to know how to read the technical specifications of the microphones and know which ones to use in particular design or installation situations. So let's start.
The following concepts will be explained in this article:
- Polar Pattern
- Frequency response
- Open circuit sensitivity
- Maximum sound pressure level
- Dynamic range
- Fantasy font
The microphones are transducers, the transducer is an element that transforms one type of energy into another, a microphone transforms acoustic energy into electrical energy, passes from sound pressure to voltage, in reality to very small voltages, we are talking about one thousand volts. That's why the technical specifications are very similar to electrical elements, do not panic if you do not understand one, here I'll try to put it in simple words.
The element is basically the type of technique used in the transducer. There are many types of microphones in the world. Coal, dynamic, capacitor, tape, piezoelectric, among many others. For effect of the article based on microphones for installation, I will explain only 2, the dynamic microphone and the condenser microphone.
Dynamic microphone: the transducer of this microphone has a fabric, called membrane, in the middle of the membrane has a coil stuck. In the axis of the coil there is a magnet that has no physical contact with the coil, when the air moves the membrane, it causes the coil to move and with the magnetic field of the magnet induces a current on it that generates a voltage, this It is a dynamic effect, very similar to hydroelectric, that's why it's called dynamic microphone.
The movement of air is caused by a sound pressure that is the audio that travels through the air. As you can see, the weight of the membrane plus the coil is high compared to the air, so dynamic microphones are not as good for detail, because high frequencies that contain less acoustic energy are not able to move the membrane. They are microphones that are very robust, they are not easily damaged, almost indestructible by very high sound pressure levels, but the voice in some solutions does not sound as good because of the lack of detail of the high frequencies.
Condenser microphone: the transducer of this microphone has a mobile membrane, but at the back it has a fixed wall, and between these two surfaces there is a dielectric material. When the membrane moves the distance of the dielectric material varies and generates a voltage, it is a capacitor effect and the name of the condenser microphone comes from the similarity of the capsule (its physical form) to the old coin-type capacitors called capacitors.
As the air has to move a very light membrane, these microphones are very good for audio with a very high definition but at high levels of sound pressure they were damaged very easily, that's why they were only used in recording studios where the environment is controlled . Currently technologies have been developed in which the condenser microphones are very easy to use and can be located in any type of application, including call systems or scenarios.
Condenser microphones require a phantom power or phantom power for 2 basic functions:
Polarize the capacitor of the capsule, that is, the membrane and the fixed wall
Power the microphone preamplifier, since the voltage generated by this transducer is very small, and you have to raise it to be able to transport it through the audio cable.
Currently there is a group of condenser microphones called Electret, these microphones have a polarized back plate with a fixed charge, that's why the phantom power required for these microphones is very low, of 11 volts and in some applications even less. In conventional condenser microphones, a phantom source of 48 v.
In another installment I will talk a bit more about the ghost source. If you have any questions you can write me through the digital version of the magazine or email firstname.lastname@example.org.
* Juan Tamayo is a senior applications engineer for Audio-Technica Latin America, with more than 10 years of experience making audiovisual projects as a designer, integrator, consultant, among other functions.