Data 1

wiki microphone: http://en.wikipedia.org/wiki/Microphone
data：http://www.mediacollege.com/audio/microphones/
评定的分量（主观客观）：
客观：
1灵敏度
2频率响应
3等效噪声级
4指向性
5动态范围
6最高声压级
7输出阻抗
灵敏度（sensitivity）：
网络：
　　灵敏度是话筒在单位声压激励下输出电压与输入声压的比值，其单位是mV/Pa。为与电路中电平的度量一致，灵敏度也可以分贝值表示。早期分贝多以单位dBm 和dBV 表示：0dBm=1mW/Pa，即把1Pa 输入声压下给600Ω负载带来的1mW 功率输出定义为0dB；0dBV=1V/μbar，把在1μbar 输入声压下产生的1V 电压输出定义为0dB。现在的分贝则以单位dBμ表示：0dBμ=0.775V/Pa，即将1Pa 输入声压下话筒0.775V 电压输出定义为0dB(这样就把话筒声压—电压转换后的电平度量，统一到电路中普遍采用的0dBμ= 0.775V 这一参考单位)。
　　显然，不论灵敏度如何表示，我们都可将它转换为dBμ，前提是行输入统一到Pa 这个单位。
　　例如：NEUMANN U89 话筒的灵敏度是8mV/Pa，可直接由20lg[(0.008V/Pa)÷(0.775V/Pa)]得出其灵敏度约为-40dBμ。
　　再如：AKG C414 话筒的灵敏度为-60dBV，由 0dBV=1V/μbar=10V/Pa 先求出1Pa 声压下-60dBV 的输出电压X： 20lg[(X V/Pa)÷(10V/Pa)]=-60 得出X=0.01(V)，即它的灵敏度为10mV/Pa。再由式20lg[(0.01V/Pa)÷(0.775V/Pa)] 可得其灵敏度约为-37dBμ。
shure官网：
Microphone Sensitivity Rating
What is microphone sensitivity?
A microphone sensitivity specification tells how much electrical output (in thousandths of a volt or "millivolts") a microphone produces for a certain sound pressure input (in dB SPL). If two microphones are subjected to the same sound pressure level and one puts out a stronger signal (higher voltage), that microphone is said to have higher sensitivity. However, keep in mind that a higher sensitivity rating does not necessarily make a microphone better than another microphone with a lower sensitivity rating.
What is "dB SPL"?
The term "dB SPL " is a measurement of Sound Pressure Level (SPL) which is the force that acoustical sound waves apply to air particles. As a person talks or sings, SPL is strongest near the mouth and weakens as the acoustical waves move away from the person. As reference levels, 0 dB SPL is the quietest sound a human can normally hear and 1 dB is the smallest change in level that the human ear can detect. For comparison, at three feet, speech conversation level is about 60 dB SPL and a jackhammer's level is about 120 dB SPL.
What about dB SPL input levels?
Microphone manufacturers normally specify one of two dB SPL input levels: 74 dB SPL or 94 dB SPL. Shure uses 94 dB SPL unless indicated otherwise on the data sheet. How do these dB SPL values relate to the real world? 74 dB SPL is typical of the sound intensity twelve inches away from a talker. 94 dB SPL is typical of the sound intensity one inch away from the same talker. A microphone "hears" these sound intensities and converts the acoustic wave into an equivalent electrical signal. To determine which SPL is used for a sensitivity measurement, look at the microphone data sheet. Confusion can arise because of the different units by which SPL may be specified. For example, 94 dB SPL = 1 Pascal = 10 microbars = 10 dynes/cm2. And 74 dB SPL = 0.1 Pascal = 1 microbar = 1 dyne/cm2. Unfortunately for the microphone buyer, different manufacturers use different units to specify SPL. But by following these dB SPL unit conversions, you can determine how different dB SPL ratings relate to each other.
What does "open circuit voltage rating" mean?
First, "open circuit" means the microphone is not connected to anything. That is, there is no electrical load on the microphone. The open circuit voltage rating indicates how much voltage appears at the microphone output when a certain SPL is introduced to the microphone diaphragm. A value for a typical dynamic mic is -75 dBV/microbar. The "V" in dBV indicates the microphone output level is referenced to 1 Volt. If there was a microphone with an output voltage of 1 volt, its level would be given as 0 dBV. The negative dBV output level ("-75") indicates that the mic output voltage is less than 1 volt (-75 dBV converts to .00018 volts). The “microbar” part indicates the microphone was tested with an input of 74 dB SPL. (Please reread the preceding section if the conversion from 1 microbar to 74 dB SPL is confusing.) To compare this typical dynamic microphone's sensitivity with a different microphone that was tested at 94 dB SPL or 1 Pascal, simply add 20 dB to the rating: -75 + 20 = -55 dBV/Pascal. Remember, to compare specifications from different manufacturers, make certain that each has been converted to the same input dB SPL level.
What is a microphone power rating?
To get a power rating, a microphone is attached to a load equal to its own internal resistance. The microphone is subjected to 94 dB SPL and the resulting power output across the load is measured. Power ratings have virtually no relevance to today's audio circuits and are now rarely used.
整理：
定义是在单位声压作用下的输出电压或电功率
对于开路灵敏度一定的传声器而言，内阻越小，功功率级灵敏度就越高，传声器的负载能力就越强。
频率响应（frequency response）
网络：
频率响应是指将一个以恒电压输出的音频信号与系统相连接时，音箱产生的声压随频率的变化而发生增大或衰减、相位随频率而发生变化的现象，这种声压和相位与频率的相关联的变化关系称为频率响应。也是指在振幅允许的范围内音响系统能够重放的频率范围，以及在此范围内信号的变化量称为频率响应，也叫频率特性。在额定的频率范围内，输出电压幅度的最大值与最小值之比，以分贝数（dB）来表示其不均匀度。频率响应在电能质量概念中通常是指系统或计量传感器的阻抗随频率的变化。
整理：
实际上指的是传声器灵敏度的频率响应，一般来说灵敏度与频率有关，不同的频率灵敏度不同。这种灵敏度随频率变化的特性就称为传声器的频率特性或频率响应。
也可以用一定频率范围内的灵敏度不均匀度表示，即在一定频率范围内最大灵敏度与最小灵敏度同平均灵敏度的差值，一篇里平均值的正负分贝值表示，称为传声器频率特性的不均匀度。
等效噪声级（LEQ Equivalent Continuous Noise Level）
网络：
NI：
Leq is a symbol that represents “Equivalent Continuous Noise Level”. Usually the signal that you are measuring is varying in amplitude. You can calculate the sound pressure (noise) level of an imaginary continuous signal, within a given time interval, that would produce the same energy as the fluctuating sound level that you are measuring.
The calculation is relatively simple; the Leq algorithm just divides the integrated sound pressure by the total duration of the signal. The result is expressed in dB.
                
                
Leq = equivalent continuous sound pressure level [dB]
p0 = reference pressure level = 20µPa
pA= acquired sound pressure in Pa
t1 = start time for measurement
t2 = end time for measurement
                
                
It is important to note that the Leq calculation is performed on time domain data, so the resultant sound level does not represent any specific band of frequencies. If you want to calculate Leq across a certain band you must first filter the data to isolate the frequency band of interest. Here is an example:
The VI SVL Leq Sound Level.vi is often used in conjunction with an A-Weighting Filter to calculate equivalent continuous A-weighted sound pressure level.
                
                
Equivalent continuous A-weighted sound pressure level is widely used around the world as an index for noise. It is defined as "the A-weighted sound pressure level of a noise fluctuating over a period of time, expressed as the amount of average energy." The result is expressed in dB(A), which gives a reasonable approximation of the human perception of loudness.
指在规定的时间内，某一连续稳态声的A〔计权 〕声压，具有与时变的噪声相同的均方A〔计权〕 声压，
则这一连续稳态声的声级，就是此 时变噪声的等效声级。噪声等效声级(分贝）数值越小越好。
整理：
在理想情况下，当作用于振膜上的生涯为零时，，传声器的输出电压应该等于零。但是，尽管传声器的震
膜并没有声压的作用，仍然有一定的电压输出。这一并不是声压的作用而引起的电压称为噪声电压。
直接比较两个传声器之间的噪声电压没什么意义
指向性（directivity）
网络：
指向性是指在频率固定时，通过声中心的指定平面内换能器响应作为发射或入射声波方向的函数。大多数
噪声源具有指向性。例如，在一给定频带下，离声源某一固定距离上，测量声源辐射的声压级时，常发现
在声源不同方向上声压级不同。许多噪声源的低频辐射几乎是无指向性的，随着频率的增高其指向性增强
。这是因振动源不同部分辐射声波到达空间各点的时间不同，因此出现位于干涉而形成不均匀的指向性辐
射。传声器的指向性有无指向性、双指向性、心脏线形指向性等之分。
Directivity is a measure of the directional characteristic of a sound source. It is often expressed as a
Directivity Index in decibels, or as a dimensionless value of Q. This is an important aspect of a sound
source, especially in a reverberant field. When a balloon is popped, it sends sound out in all
directions equally (for all practical purposes), and this would represent a Q value of 1. A person
talking has a Q value of approximately 2, which means that sound radiates in a hemispherical
pattern (half a sphere). Directivity is important because it helps indicate how much sound will be
directed towards a specific area compared to all the sound energy being generated by a source. If
you have a limited amount of sound energy available (like that produced by the human voice), you
can increase the distance that your voice will cover by increasing the directivity of your voice. You
have probably experienced this calling to someone outdoors, when you cup your hands around your
mouth to increase the directivity. What you are doing is "directing" more of the sound generated by
your voice in the direction you need it to go. Someone talking through a megaphone may improve
their voice's Q value to 15-20. You could think of this like a nozzle on your garden hose. Your garden
hose will deliver a fixed amount of water, you can spray it in a mist to cover a wide area, or you can
shoot it in a stream to a distant location, it's the same amount of water either way.
In a reverberant space, directivity plays another role. A low Q source, like a person talking, or a
balloon popping will excite the reverberant field very uniformly. This limits the distance you can
communicate before speech is masked by the reverberant sound. If you could increase the amount
of sound that was directed towards your target, and at the same time reduce the amount of sound
that went off in all directions to add to the reverberant field, you could increase the distance you
could communicate. This is what increased directivity does for you. Unlike the outdoor case we
described above, where the unused sound is lost forever, in a reverberant space the unused sound
bounces around and adds to the background noise. A high directivity source, like a voice through a
megaphone, can significantly increase the effective communication distance.
Loudspeakers have to be selected on the same basis for use in reverberant spaces. This is part of the
sound system design process for us, we evaluate the reverberation time of the space, and determine
what the directivity of the loudspeaker has to be to communicate over the distances required. It is
possible to have reverberation times so long that it is impossible to select a directional enough
loudspeaker to work effectively. The situation is complicated further if there are several loudspeakers
involved. The loudspeakers that don't point towards you just contribute to the reverberant field you
hear, without contributing to the useful sounds you hear. In very reverberant spaces, where one
speaker may have worked, adding four or five speakers may prove to be unworkable. This is why
directivity is a critical specification for difficult acoustical environments. Here's a discussion on
Loudspeaker Directivity as a Design Issue.
指向性麦克风的分类：
心形指向
  这种指向得名于它的拾音范围很像是一颗心：在话筒的正前方，其对音频信号的灵敏度非常高；而到了话
筒的侧面（90度处），其灵敏度也不错，但是比正前方要低6个分贝；最后，对于来自话筒后方的声音，
它则具有非常好的屏蔽作用。而正是由于这种对话筒后方声音的屏蔽作用，心形指向话筒在多重录音环境
中，尤其是需要剔除大量室内环境声的情况下，非常有用。除此之外，这种话筒还可以用于现场演出，因
为其屏蔽功能能够切断演出过程中产生的回音和环境噪音。在实际中，心形指向话筒也是各类话筒中使用
率比较高的一种，但是要记住，像所有的非全向形话筒一样，心形指向话筒也会表现出非常明显的临近效
应。
超心形指向
  这种指向类型与过心形指向非常相似，也经常被混淆，但是，一般超心形指向类型的指向性要比过心形稍
稍差一些，且其对来自话筒后方声音的灵敏度区域也要小得多。
过心形指向
  这种指向类型同心形指向和超心形指向非常相似，因为它们都是对话筒前方声音的灵敏度非常高。但是，
它们的最低灵敏度所处的点位是不同的，比如，心形指向是在话筒的正后方，超心形是在200到210度处，
过心形是在150到160度处，这就是为什么过心形指向话筒的指向性要比心形指向和超心形指向的话筒要好
的原因了。实际中，这种过心形话筒多用于需要最大限度隔离音源的录音环境中。
全向形指向
  这种指向类型的话筒，顾名思义，就是对来自话筒周围各个方向的音频信号的灵敏度都是同样高的。这种
话筒的最大优点就是不会产生明显的临近效应。
8字形指向
  有时，也被叫做是双指向形，因为这种指向类型的话筒对来自话筒正前方和正后方的音频信号具有同样高
的灵敏度，但是对来自话筒侧面的信号不太敏感，这样，其拾音范围呈现在图纸上，就很像是一个8字，而
话筒的位置就正好处于这个8字的切分点上，故而得名。
整理：
传声器对不同角度入射的声压的响应
动态范围（Dynamic Range）
网络：
动态范围是指音响系统重放时最大不失真输出功率与静态时系统噪声输出功率之比的对数值，又指一个多
媒体硬盘播放器输出图像的最亮和最暗部分之间的相对比值。 单位为分贝(dB)。一般性能较好的音响系统
的动态范围在100(dB)以上。
wiki：http://en.wikipedia.org/wiki/Dynamic_range
整理：
传声器的最高声级（dB）与等效噪声级（dB）之差表征的，他是传声器动态范围的上限，在这一声级时，
传声器的非线性失真应不超过某一规定值。传声器的灵敏度越低，相应的最高升级至就越大，反之相反。
优质传声器的动态范围可高达110dB
输出阻抗与负载阻抗（output impedance）
网络：
Microphone Impedance
When dealing with microphones, one consideration which is often misunderstood or overlooked is
the microphone's impedance rating. Perhaps this is because impedance isn't a "critical" factor; that
is, microphones will still continue to operate whether or not the best impedance rating is used.
However, in order to ensure the best quality and most reliable audio, attention should be paid to
getting this factor right.
If you want the short answer, here it is: Low impedance is better than high impedance.
If you're interested in understanding more, read on....
What is Impedance?
Impedance is an electronics term which measures the amount of opposition a device has to an AC
current (such as an audio signal). Technically speaking, it is the combined effect of capacitance,
inductance, and resistance on a signal. The letter Z is often used as shorthand for the word
impedance, e.g. Hi-Z or Low-Z.
Impedance is measured in ohms, shown with the Greek Omega symbol Ω. A microphone with the
specification 600Ω has an impedance of 600 ohms.
What is Microphone Impedance?
All microphones have a specification referring to their impedance. This spec may be written on the
mic itself (perhaps alongside the directional pattern), or you may need to consult the manual or
manufacturer's website.
You will often find that mics with a hard-wired cable and 1/4" jack are high impedance, and mics
with separate balanced audio cable and XLR connector are low impedance.
There are three general classifications for microphone impedance. Different manufacturers use
slightly different guidelines but the classifications are roughly:
Low Impedance (less than 600Ω)
Medium Impedance (600Ω - 10,000Ω)
High Impedance (greater than 10,000Ω)
Note that some microphones have the ability to select from different impedance ratings.
Which Impedance to Choose?
High impedance microphones are usually quite cheap. Their main disadvantage is that they do not
perform well over long distance cables - after about 5 or 10 metres they begin producing poor
quality audio (in particular a loss of high frequencies). In any case these mics are not a good choice
for serious work. In fact, although not completely reliable, one of the clues to a microphone's overall
quality is the impedance rating.
Low impedance microphones are usually the preferred choice.
Matching Impedance with Other Equipment
Microphones aren't the only things with impedance. Other equipment, such as the input of a sound
mixer, also has an ohms rating. Again, you may need to consult the appropriate manual or website
to find these values. Be aware that what one system calls "low impedance" may not be the same as
your low impedance microphone - you really need to see the ohms value to know exactly what you're
dealing with.
A low impedance microphone should generally be connected to an input with the same or higher
impedance. If a microphone is connected to an input with lower impedance, there will be a loss of
signal strength.
In some cases you can use a line matching transformer, which will convert a signal to a different
impedance for matching to other components.