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Microphone technical parameters

Author:admin   AddTime:2021-02-19

Microphone
Microphone sensitivity
There are several ways to explain the sensitivity of the microphone:

dBV per microbar:
Measure open circuit (Open Circuit) at a sound pressure level of 74 dB (dBSPL; Decibel-Sound Pressure Level)
Microphone, (remember the big V? It was built under 1V).

mV / Pa:
Measure the millivolt (millivolt, 1 × 10-3) of an open microphone at a sound pressure level of 94 dB.

dBm / 10 dynes / cm2:
At a sound pressure level of 94 dB, the measured microphone is matched to a specific impedance; the dB number is less than 1 milliwatt
(milliwatt, 1 × 10-3 ).

dBm, EIA Rating:
At a sound pressure level of 0 dB, the measured microphone is matched to a specific impedance;
The dB number is less than 1 milliwatt (milliwatt, 1 × 10-3).

There are several different ways, but the same is to express sensitivity:
1. Open Circuit Sensitivity: -60 dBV / μbar: Another way of saying -60 dB is,
___ can be determined to be capable of conversion or equivalent to 1 volt per μbar (Microbar).

This means: when the microphone is connected in an open-circuit state (the input impedance of the measuring instrument is greater than the output impedance of the microphone
7 times the value), and in a sound pressure level environment of 1 μbar (74 dBSPL); it produces -60 dBV (1 mV)
The output voltage, that is, the 74 dB sound pressure level makes the microphone produce an output voltage of -60 dBV (1 mV).

2. Open Circuit Sensitivity: 10 mV / Pa (10 millivolts per Pascal).
This means: the microphone is applied with 1 Pascal (94 dBSPL) under no load; it can produce
10 millivolts output. That is, the microphone generates 10 millivolts (-40 dBV) at a sound pressure level of 94 dBSPL

Output.



Microphone technical parameters


3. Open Circuit Sensitivity: -40 dBV / Pa (-40 dB is equivalent to 1 Volt).
This microphone can produce an output of -40 dBV without load. This microphone is at 1 Pascal (94 dBSPL)
And without a load, it can produce an output of -40 dBV. That is, the microphone is at a sound pressure level of 94 dBSPL
Can produce -40 dBV output under the level.

4. Power Sensitivity: -38 dBm per 10 dynes / cm2 (per 10 dynes / cm2-38 dBm).

When the microphone is connected to an equal input impedance; this is under load.
It is stated that at 10 dynes per square centimeter “94 dBSPL”, an output of -38 dB can be produced; this can be regarded as
"Equivalent to" 1 milliwatt. This also states that a sound pressure level of 94 dB can produce an output of -38 dBm.

5. EIA sensitivity (Electronic Industries Association U.S.A. Sensitivity): -132 dBm 1 milliwatt.
This EIA (Electronic Industries Association of America) is recognized as correct and the ratio specification used is publicly recommended. The output of each microphone is matched
The load is granting a specific sound pressure level; this specific sound pressure level is 0 dBSPL.

SPL + dBm (EIA) = dBm output through a matched load.
All equivalent sensitivity specifications are as follows:

-60 dB 1 V / μbar = 10 mV / Pa = -40 dB 1V / Pa = -38 dBm / 10 dynes / cm2 = -132 dBm EIA.

annotation:
dBV: Take the 74 dBSPL sound pressure level of the average human voice as the reference standard, which is equal to 1 microbar (1 μbar)
The pressure is applied to the microphone, and then the signal voltage output of 1 Volt is converted.


On the pressure theory:
milli = m (milli) is 10-3 = 0.001, then 1 millibar (millibar) = 0.001 bar.
micro = μ (micro) is 10-6 = 0.000001, then 1 microbar (microbar) = 0.000001 bar.

Pascal is a noun of physics in Chinese, named after a person’s full name Blaise Pascal 1623 ~ 1662,
He is a French mathematician, physicist, and philosopher. In his early years, he measured atmospheric pressure with a mercury column and found that the higher the distance from sea level, the lower the pressure.
This difference can be known from the height of the mercury column, which is the Basque principle.

Basque's principle: When pressure is applied to any part of the liquid within the limit, the pressure will be transmitted equally to all parts in the liquid without increasing or decreasing.
That is, when one part of the boundary liquid is under pressure, the other parts must also be under the same pressure.
Named after Pascal’s discovery, it is named after Pascal’s principle.


Dyne is called "Dyne" in Chinese, also referred to as "Da", but it is rarely used. Da is named after a person because of a noun in physics.
It is a unit in the CGS system (centimeter-gramme-second). It is an absolute unit for calculating "force".
The force acting on 1 gram of mass can make this mass obtain an acceleration of 1 cm per second (Centimeter; centimeter) is called
"1 Dyne".

The force of 1 gram of a unit of gravity is equal to 980 dynes.
The reason why it has a place in physics is mainly because it is "small", which is equivalent to the force that makes 1 gram of mass produce 1 cm/sec 2 acceleration, and 1 dyne is equal to 0.00001 Newton.

Dyne centimeter (dyne centimeter) is a noun in physics, an absolute unit for calculating "work", and is also commonly known as "erg."

Erg (Erg) was formerly called "Erg", a term in physics, and an absolute unit for calculating "work".
Acting on an object with a force of 1 dyne moves the point of application by 1 cm, which is the absolute unit of work and is called an erg.
In practice, 107 times the erg is often used as an absolute unit of work, also commonly known as "joules."

Joule (Joule) is a noun in physics, named after Joule.
Jomes Prescott Joule was a British physicist from 1818 to 1889 and a disciple of Dalton. Joule devoted his life to physics and
He has written a lot of chemical experiments, invented the method of generating heat by galvanic electricity, measuring the work equivalent of heat, and building energy immortality theory.
Joule is an absolute unit of "work" or "energy" in practice. In general, 10,000,000 erg is 1 joule.

In the theory of work, the work done by a force of 1 Newton and its point of action moved 1 meter in the direction of the force.

0 dB = 0.000,2 microbar (20-4) = 0.000,2 dyne / cm2 (20-4) = 0.000,02 newton / m2 (20-5) = 0.000,000,000,002 watts / m2 (20-12 ),

Therefore 1 microbar = 1 dyne / cm2 = 0.1 newton / m2,
Or 10 microbar = 10 dyne / cm2 = 1 newton / m2.
  
Pressure_______________ is equal to

1 lb / ft2___________ 127.6 dBSPL
1 lb / in2____________170.8 dBSPL
1 newton / m2_________94 dBSPL
1 microbar___________74 dBSPL
1 microbar___________1 dyne / cm2
1 microbar___________1 / 1,000,000 atmos _______________

  
The above information is to tell you the measurement data rules of a microphone, and how these scientific announcements are used by later generations.
From an expensive and good-quality microphone product, they dare to publish the data obtained in the specification sheet.
In the early days, people finally made products that met the conditions, especially the microphones of Eastern European countries at that time.
It is really durable and standard! Often pioneers, slowly, the technology shifts, and various styles of microphones appear,
Only under the commercial market competition, the technical information in this area will become more and more chaotic, it is best to let you see clearly! Haha! !

This information has been around me for a long time. Don’t laugh at me. I can’t remember it at all. What I can remember and apply in the work site is,
The sound pressure that the sound body can sense when facing the sound head at a distance of about 20 cm is its sensitivity value. The simplest explanation is in the microphone
In the attachment, if the label is written like this:


Sensitvity (1000 Hz Opne Circuit Voltage)
-54 dBV / Pa (1.85 mV)
1 Pa = 94 dB SPL
150Ω

Don’t worry about any number or reference data. Look at the negative sensitivity data-54 dB. If you use math to find this value,
It will be a very, very small voltage value, which is not enough to use, so you must use the microphone attached to the audio platform
Gain amplifier (Gain or Trim) adjust it to +45 dB position, you will get close matching microphone amplification value,
This approach may not be the most standard, but when applied in the field, it will quickly make your Vocal microphone settings the fastest
Positioning time! When the level position is in sequence, it depends on whether the application feature is Low cut or equalization repair.


Another thing that must be explained is that with the establishment of basic physical concepts, many people tend to misunderstand one thing, that is, the two microphones
For comparison, when the output of a certain microphone is relatively loud on the same channel and the same gain data,
Just decide which microphone is better! is it you? If you have this idea, please correct it as soon as you read this article.
The impedance level will also affect the microphone positioning output size, but it is not the absolute quality of the microphone.
_

SHURE BETA-52 frequency response chart
  
The frequency response diagram will be drawn in the standard microphone specification table (we have introduced it before).
They will tell you what the frequency response of the sound is at the so-called standard distance, at what distance or angle or how, don’t underestimate its label, let’s use the Shure Beta-52 bass drum microphone that every family has to explain , If you put the microphone 3mm inside the bass drum, it means sticking to the drum skin very close, telling you, that is impossible! When the bass drum was stepped on, the head of the drum had bounced off the microphone!

Think about it carefully. Generally, there is as much as 10 cm between the head and the drum head. Ok, look at the curve. What is the low frequency response at 6 cm. Therefore, after adjusting the bass drum in the main speaker system, you still need the help of the subwoofer. Ascend this bass drum low-frequency atmosphere, you can use EQ to compensate! Yes, but it is limited. If the sound compensation to the outside field is satisfactory, then when you use headphones or the recorded sound, it is absolutely funny. The more serious thing is to adjust the frequency range too much. Make the power amplifier use up the precious Head Room early, so the amplifier is fully loaded early. And if you lower the live sound pressure to protect it, it will make the overall sound pressure of the broadcast insufficient. It's a good thing, a big drum can actually make you dead!

SHURE BETA-52 Frequency Pointing Chart
Next is that under the marked distance, the protruding 3 ~ 4 Khz frequency domain value is almost unchanged, so before you adjust the EQ, you can get the bright drum skin, understand, don’t be happy, see another A picture, you can see that it marked several frequency points, regardless of the beautiful pointing characteristics, please look at those frequency domains that start to have a long tail. This story tells us that the higher the frequency, the wider and longer the tail! Unfortunately, a Guitar Amp was placed in front of the drum, ha! This is really how it turns out... play it yourself.

See clearly the specifications and characteristics of the equipment you bought. You must develop a habit with the * number, even if the merchant adds soup and ingredients,
You only need to compromise the data to know its characteristics, so that you can use it smoothly when you go out, and tell the story from the above picture.
How to understand the temperament and personality of microphones, share with you.

The types of microphones can be divided into four commonly used types, which are almost always encountered in our work field.
We now come to know or review the types of these microphones.
  
Omni-Directional Polar Pattern (omnidirectional)

Bi-Directional Polar Pattern (two-pointing)
 Omni-Directional Polar Pattern (omnidirectional)

It can be seen that it has the characteristics of omni-directional radio by referring to the diagrams, that is, the radio sensitivity of any direction is almost the same.
But that is an ideal physical environment. The grip, that is, the back of the capsule, must be a little bit sunken, and the frequency response will not be the same.


  Bi- Directional Polar Pattern (Bi-directional)

The level and frequency response picked up on both sides of the capsule are the same. Relatively, like the characteristics of two capsules, it will naturally generate two sets of Dead Spots (no radiation zone) at 90° and 270°. .
  
Uni- Directional (Cardioid) Polar Pattern
(One-pointing heart-shaped)
Super-and Hyper Cardioid Polar Pattern
(Super pointing sensitive)
Uni- Directional (Cardioid) Polar Pattern
(One-pointing heart-shaped)

This is the most natural and the characteristic of most dynamic microphones. The Dead Spot (non-radiation zone) is the deepest non-reaction zone in the opposite direction of 180°. Therefore, the sound signal from behind the head is the least Will be picked up, which is also the easiest physical characteristic of the general dynamic capsule manufacturing process. Relatively used in stage performances, when there is a monitor speaker behind the capsule, its influence value is very low.

  Super-and Hyper Cardioid Polar Pattern
(Super pointing sensitive)

In order to achieve the sensitivity and facsimile response of the audio head, the capacitive structure of the audio head was naturally born.
The characteristic of the long tail behind the capsule is the condenser microphone. All kinds of microphones have the most livelihood, the widest frequency response,
The frequency characteristic is the flattest. Although it is not shockproof, it is prone to damp and noise, and an additional power supply is required. However, in recording studios, radio stations, live singing and other occasions, almost all microphones of this type are used.


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