| Electronic Condenser Microphone: |
|
One of the most important types of commercial microphones is that which uses a
capacitor (in the early days of electronics, this component went by the name of
condenser) The conventional form of this instrument is one in which the charge
on the capacitor is essentially constant. This maybe realised by connecting a
voltage source to one of its two electrodes through a large resistor (the other
electrode being grounded). Alternatively, the fixed external charge, Q, stored
by the capacitor may derive from the permanent electric polarization of a dielectric
material, such as polymer. Charges in spacing between the diaphragm and a back
plate, due to impinging sound waves, give rise to a voltage variation across the
terminals of the capacitor Instruments of this type are referred to as electret
condenser microphones (ECM). |
| Sensitivity: |
|
The sensitivity is defined as the output voltage for a specified acoustic stimulus
and load condition. In this catalog it is expressed in (dBV/10 bar). In the case of
dynamic types it is expressed as the open circuit voltage appearing at the output
terminals. In the case of electret type it is expressed with a specified resistive
load and supply voltage since the output resistance tends towards constant current
characteristic. |
| Output impendence: |
|
The output impedance represents the internal electric resistance within a microphone
as seen from the side of output terminals of the microphone. In the case of ECMs,
the effective output resistance is determined mainly by the value of load resistance.
it can be made higher or lower by the value of load resistance with a corresponding
change is sensitivity. |
| Frequency Response: |
|
The frequency response of a microphone is value indicating which frequency range,
from the lower to the higher range. In other words, it is the frequency range which
the microphone can receive sound. It is expressed as 50Hz~1500Hz. |
| db (Decibel): |
|
A dB is a way of expressing a ratio of two numbers. For acoustic pressure
the expression is dB=20log (P1/P2). So, if P1 is 100 times greater than P2, P1 is
40 dB greater than P2. dBV=dB relative to 1 Volt. |
| Dynamic Range: |
|
Dynamic range describes the ratio of the softest sound to the loudest sound in
a musical instrument or piece of electronic equipment. This ratio is measured in
decibels (abbreviated as dB) units. Dynamic range measurements are used in audio
equipment to indicate a component's maximum output signal and to rate a system's
noise floor. As a reference point, the dynamic range of human hearing, the difference
between the softest sound we can perceive and the loudest, is about 120 dB.
|
| SPL (Sound Pressure Level): |
|
SPL is short for Sound Pressure Level, which is a convention for expressing loudness.
The units are dB SPL. 0dB SPL has been assigned to 20uPa, which is about the lower
threshold of hearing. Sound pressure drops as distance from the sond source increases.
At a five foot distance, the SPL of a normal speaking voice is about 60 dB SPL on average. |
| Directional: |
Depending on various aspects of a microphone's construction, it may be nearly
equally sensitive to sound coming in all directions (an omnidirectional microphone),
or it may be more sensitive to sound coming from a particular direction (a unidirectional
microphone). The most common of the unidirectional type is sometimes called a cardioid
microphone, because the sensitivity pattern somewhat resembles the shape of a heart; most
vocal mikes are cardioid or hyper-cardioid (similar to cardioid but with a tighter area
of front sensitivity and a tiny lobe of rear sensitivity.)
Some microphones have more complex sensitivity patterns. Most ribbon microphones are
bi-directional, receiving sound from both in front and back of the element. This type of
response is also known as a figure-8 pattern, because of its shape. Shotgun microphones,
the most directional form of studio microphone, reserve most of their sensitivity for
sounds directly in front of, and to a lesser extent, the rear of the microphone. Shotgun
microphones also have small lobes of sensitivity to the left and right. This effect is a
result of the microphone design, which generally involves placing the element inside of
a tube with slots cut along the side; wave-cancellation eliminates most of the off-axis noise.
A parabolic microphone uses a parabolic reflector to collect and focus sound waves onto a
microphone receiver, in much the same way that a parabolic antenna (e.g. satellite dish)
does with radio waves. Typical uses of this microphone, which has unusually focused front
sensitivity and can pick up sounds from many meters away, include nature recording,
eavesdropping, law enforcement, and even espionage. Parabolic microphones are not typically
used for standard recording applications, because they tend to have poor low-frequency
response as a side effect of their design. |
| FET: |
|
A field-effect transistor (FET) is a type of transistor commonly used for weak-signal
amplification (for example, for amplifying wireless signals). The device can amplify
analog or digital signals. It can also switch DC or function as an oscillator. |
| Noise cancelling: |
|
A noise cancelling microphone (also known as pressure gradient or close talking)
is a directional microphone designed for use close to the talker's mouth. Its
directional pattern looks like a figure 8, and is called cosine or bidirectional.
Thus, the front and rear ports are interchangeable. This microphone is used in
headset booms or hand-held microphones. It provides the greatest signal-to-noise
ratio available for acoustically transducing a person's voice. |
