Impedance has been a decisive factor for many sound operators. Personally, I don't think it's that important, because professional microphones currently have a more stable impedance.
Juan Tamayo*
In the previous installment we addressed topics such as Polar Pattern, Phantom Source and Frequency Response. Basically we talk about the technical qualities of a microphone that allow you to deliver the "sound color", a term used in recording when it is not required to apply filters to a microphone to find the desired sound, because it already has it.
"Digital" Frequency Response
This term has confused audio professionals a lot, because they misinterpret the sample rate believing that it is the maximum capture frequency, for example, when they talk about a microphone like the AT2020USB+ which is an AT2020 analog microphone with a digital converter with USB connection to a computer whose characteristics are 16 bits at 44.1/48 kHz.
44.1/48 KHz is not the maximum frequency, this frequency is the amount per second that the A/D converter samples. For this case it takes 44,100 or 48,000 samples per second, at a resolution of 16 bits, the sample can have up to 65,536 values.
Frequencies above 40 KHz are spoken of in order to comply with the Nyquist-Shannon theorem and thus be able to reconstruct the sound signal acceptable to the human ear.
Open circuit sensitivity
For me, it is one of the most important qualities of a microphone, because open circuit sensitivity is directly linked to the ability to produce voltage according to the movement of the capsule. The more voltage you produce, the more sensitive it is.
It is defined as the voltage produced by a microphone when a 1 pascal (94 dBspl) sound power source with a tone of 1 KHz is produced one meter away. This voltage, being less than the reference voltage (0.775v), will be a negative value, so the reader should be careful when comparing sensitivities, for example -60 dB will be less than -50dB.
To get a clear idea of the sensitivity, it is as if you were given to choose two cars exactly the same, but one travels 100 KM with a gallon and the other 200 Km with the same gallon of fuel, which one would you choose? In the case of microphones, having a better sensitivity will make the gain of the console preamplifier more closed, so it will avoid possible electrical noises from the system.
Impedance
Impedance has been a decisive factor for many sound operators. Personally, I don't think it's that important, because professional microphones currently have a more stable impedance. What we must know is how the impedance affects the preamplifier, for example, very low impedances, less than 50 ohms, will require a very high transport current in the preamplifier, making the voltage wave high and generating possible distortions when capturing the sound.
Very large impedances generated with coupling transformers make the signal have a filter pass band eliminating competent in low and high frequencies, but achieving that the audio signal can travel in long microphone signal cables without losing much energy (ideal for analog call systems).
The important thing about this feature is to know how the performance of the microphone for your application will affect the impedance that it has.
Maximum Sound Input Level
As the name implies, it is the maximum level in sound pressure dB-SPL that a microphone can withstand before being damaged, currently Audio-Technica develops condenser microphones above 140 dB, the human ear pain threshold is 120 dB.
Dynamic microphones do not possess this maximum level because, in theory, they are indestructible.
Noise
Noise is the sound produced by the electronic circles of the microphone, and it will always be a constant variable and will be the floor sound level of any microphone.
Dynamic Range
Dynamic range is the mathematical difference between Maximum Input Level and Noise, for example, if you have a microphone of 150 dB-SPL of MNE, but its noise is 130 dBspl, the dynamic range will only be 20 dB.
Conclusions?
Dynamic microphones do not have dynamic range.
Signal to Noise Ratio: As audio does not work at maximum and minimum levels, this term informs us what is the difference between the minimum useful signal and the typical working signal (94 dB-SPL, 1 Pascal). The minimum useful signal is when it exceeds the microphone noise.
Microphone Body: This term refers to the physical construction of the microphone, it is not defined as a datasheet feature, but I have included it so that the reader can analyze the location of the microphone for the desired application, for example, if it requires a microphone that does not take up much space and is located on a podium, the ideal is to use a gooseneck microphone and not a handheld microphone in a pedestal boom. When selecting a microphone for an installation, please make sure it is the microphone with the desired body or shape.
With this article we have concluded a brief description of the most important features of a datasheet of any professional microphone. Remember that the microphone is where the mechanical signal that you or your project wants to transmit enters. If it goes wrong, it will most likely go wrong.
If you have any questions or want to know more about microphones, technologies and products please do not hesitate to contact me. Currently I technically serve the markets of Brazil, Mexico and the Caribbean for Audio-Technica (www.audio-technica.com)
*Juan Tamayo is a senior application engineer for Audio-Technica Latin America, with more than 10 years of experience performing audiovisual projects as a designer, integrator, consultant, among other functions. You can write to the mail [email protected]
