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New explanation of speaker sensitivity

2021-10-11 570
In audio equipment, the electrical-acoustic or acoustic-electric conversion capability of the equipment is called the sensitivity of the equipment. For active speakers, sensitivity refers to the magnification of the internal amplifier and the sensitivity of the speaker combination. Small power sources such as a Walkman with a large magnification and a small audio output power are loud. For passive speakers, sensitivity refers to the loudness of the sound generated at 1M when the speaker combination gives the speaker a 1000Hz signal of 1W in the power amplifier system. Sometimes some audio systems are forced to lower their sensitivity for the sake of sound quality and stability of work. In addition to excluding the factor of the manufacturer's false standard power, the main reason for this phenomenon is that the sensitivity of the speakers is different.
 The sensitivity of speakers may be the most misunderstood of various common indicators. For a long time, the amplitude-frequency response of speakers has often been simplified to a single value, which is sensitivity. This is the source of misunderstanding. Some people think that this value represents the loudness of a certain speaker when reproducing a signal; others think that the loudness of two speakers with the same sensitivity is the same when reproducing the same signal. Both views have limitations. In fact, the sensitivity of the speaker only reflects the sound pressure level of the speaker when it is aimed at a specific bandwidth and spectral content signal. In other words, if two speakers with the same sensitivity index have different frequency responses, the output sound pressure level may be different when the same signal is reproduced.

In audio equipment, the narrow sensitivity concept mainly involves electroacoustic equipment such as microphones and speakers; the electrical equipment involved includes power amplifiers, mixers and peripheral equipment.

1. According to the different conditions of the unit used and the connected load, the common microphone sensitivity includes open circuit sensitivity and load sensitivity.

a. Regulation of open circuit sensitivity: Under the action of unit sound pressure, open circuit sensitivity = open circuit voltage/sound pressure on the microphone diaphragm.
The unit of the reference value is different, and the calculated result of open circuit sensitivity is also different. my country generally uses mv/pa or v/pa as the unit. It can be seen that the sensitivity expressed in dB must be marked with the reference value (that is, whether the value of 0dB is v/u bar or v/pa), otherwise the sensitivity label will have no reference value.

New explanation of speaker sensitivity

b. Load sensitivity is the power representation of sensitivity. It refers to the output power of the microphone output terminal on the rated load under the unit sound pressure, the unit is mw/u bar, and the rated load is generally 600Ω. Generally, dBm can be used to indicate the electrical power sensitivity, and the reference value at this time is 1mv/u bar.
At the same time, the sensitivity of the microphone is also related to the measured frequency point (usually 1KHZ). This sensitivity is called a certain frequency sensitivity; if the average value is taken within a certain frequency range, it is called the average sensitivity.
The concept of microphone sensitivity also involves the issue of sound pressure. If it is calculated using the sound pressure value at a certain point in the sound field, it is called sound field sensitivity; if it is calculated directly using the sound pressure on the microphone diaphragm, it is called sound pressure. Sensitivity.

2. The sensitivity of a speaker was originally defined as the sound pressure value generated by the speaker under the action of a unit voltage.

The sensitivity of a speaker is similar to that of a microphone. In the earliest definition, it was defined as the sound pressure value generated by the speaker under the action of a unit voltage. However, this definition does not consider the input voltage combined with the impedance of the speaker, which makes the sensitivity lose its reference value; at the same time, the sensitivity of the speaker needs to reflect its signal conversion ability to specific power, rather than the conversion ability of voltage signals, so for To better characterize the electromechanical conversion capability of a speaker, it is generally stipulated that the sound pressure level measured at a certain distance after a certain power signal is applied to the speaker is called the sensitivity of the speaker, which is dB/m/W.
Similarly, the sensitivity of a speaker is directly related to the frequency of the signal, and it is also related to the type of signal. Whether the sensitivity is 1KHZ or 500HZ, whether it is a pink signal or a sine wave signal, the sensitivity value of the speaker has different labels.

Input and output levels. The input and output interfaces of audio equipment generally have level value marks or selection keys, such as: 0dBm, 0.775v, +4dB, 0dBu, etc. Among them, the level value at the input interface of the device is generally the input sensitivity of the device, so sometimes the input and output level labels can be classified as the sensitivity category. But not all interface levels have the meaning of sensitivity.
The input level value of the device represents the signal level value that the device allows to input (most of the time there is a rated value and a maximum value). Under normal circumstances, when the signal is input at the rated level value (0dB), the device has a rated output value (may be power or level)

Generally, the input level of a device is generally closely related to its input sensitivity. Each device and input level or the rated input level range in a certain mode may be different (that is, the sensitivity is different), some are only marked with 0dB, and some have -10dB and +4dB or +10dB for selection. Usually it should be set uniformly according to the equipment or system. Otherwise, if the input signal level value is lower than the input sensitivity, the output power or level of the device will be insufficient; if the input signal level value exceeds the input level range of the device , It will cause distortion of the device output.

The output level of the device is similar to the input level, but the output level of the device has more specific requirements for the connected load impedance. In general, the 0.775v = 0dB specified for the output level is based on a load with a certain impedance (usually 600Ω). If the load impedance increases, the output level value may also increase.

In addition, there are some input and output levels expressed in the form of DBV and DBU. The general rule is: 0dBv=1.0V 0dBu=1.0uV. From the above analysis and comparison of sensitivity and level, it can be seen that: Sensitivity is different in value, meaning is also different, and the reference value is also different. Even for devices of the same type, their sensitivity may vary greatly in value.

Generally, the sensitivity of dynamic microphones is lower, usually: 0.2 mv/pa ~ several mv/pa, while the sensitivity of condenser microphones is higher, usually: several mv/pa ~ more than ten mv/pa Even dozens of mv/pa, but the sensitivity of ribbon condenser microphones is lower.

Generally, the sensitivity of the tweeter is higher, and some can reach more than 100dB/m/W (this is why the tweeter attenuation network is added in the speaker); usually the sensitivity of the woofer is lower, and the low may only be 80 dB/m /W around. For other devices, the input sensitivity is generally based on 0dB, but a few devices have -10dB and +4dB to choose from. The maximum input and output levels are quite different. In the case of no distortion, it may be +10dB, +15dB, or it may be +24dB, +32dB or even higher.
The sensitivity of audio equipment is a very useful indicator, sound engineers and engineering technicians often need it to calculate the recording or sound reinforcement gain, level, select the microphone, determine the power configuration of the system and the sound pressure level of the sound reinforcement, and the connection mode of the system , Port settings, etc. If the concept of sensitivity is neglected in audio technology, there may be equipment distortion, insufficient dynamics, unsatisfactory sound pressure level, excessive equipment load, and other sound indicators being affected.
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