1、 The role of the processing system
1. Mixing console: The mixing console is mainly used in audio systems for processing signal sources: amplifying weak signals from microphones, impedance matching, corresponding timbre modification, and integrated control of various sound sources. In professional recording and stage performance, the mixer also has multiple marshalling output, digital analog format conversion, audio and video positioning and editing functions.
A high-quality mixing console should meet the following basic technical specifications:
*Total noise: -86.5dBu (20Hz~20kHz)
*Total harmonic distortion THD:<0.007% (1kHz @+14dBu, 20Hz~20kHz)
*Channel crosstalk: -84dBu（ 1kHz@0dBu ，20Hz~20kHz)
*Frequency response: -1dB@20Hz ~60kHz， -3dB@20Hz ~100kHz (microphone input to any output)
*Equivalent Input Noise (EIN): -129.5dBm (microphone input at maximum gain, 150 µ m terminal)
*Common mode rejection ratio CMR:> 90dB@1KHz
*Maximum input level:+22dBu
*Main output maximum level:+28dBu
*Other output maximum level:+22dBu
*Microphone input impedance: 1.3k Ω
*Line input impedance: 10k Ω
*Output impedance: 120 Ω
2. Equalizer
Due to the resonance characteristics of the sound field, different absorption coefficients of sound-absorbing materials for sound frequencies, and uneven frequency response characteristics of speakers, problems such as excessive sound at certain frequencies and insufficient sound at certain frequencies may occur. However, the equalizer on a typical mixing console can only adjust the high-frequency, mid frequency, and low-frequency electrical signals separately, and cannot achieve precise frequency equalization. The function of an equalizer is to adjust the amplification of various frequency components of electrical signals separately, compensate for the defects of speakers and sound fields by adjusting the electrical signals of different frequencies, and compensate for and modify various sound sources and other special effects (frequency equalization).
Equalizers are mainly divided into two categories based on their circuits: graphic equalizers and parametric equalizers. Graphic equalizers have a simple and intuitive structure, and are widely used in professional audio.
The graphic equalizer, also known as the chart equalizer, can intuitively reflect the balanced compensation curve through the distribution of push and pull buttons on the panel, and the increase and decrease of each frequency are clear at a glance. The graphic equalizer adopts constant Q-value technology, and each frequency point is equipped with a push-pull potentiometer. Regardless of whether a certain frequency is raised or attenuated, the frequency bandwidth of the filter remains unchanged.
The commonly used professional graphic equalizer divides the 20Hz~20kHz signal into 10, 15, 27, and 31 segments for adjustment. Users can choose different numbers of graphic equalizers according to their requirements. Generally speaking, the frequency points of a 10 band equalizer are distributed in octave intervals and are used in general situations; 15 segment equalizer distributed at 2/3 octave intervals, used in professional sound reinforcement; The 31 segment equalizer is distributed at 1/3 octave intervals and is mostly used in situations where fine compensation is required.
A high-quality equalizer should meet the following basic technical specifications:
*Total noise: -92dBu (20Hz~20kHz)
*Total harmonic distortion THD:<0.01% @+20dBu
*Channel crosstalk:<-80dBu (20Hz~20kHz)
*Frequency response: ± 2.5dB
*Maximum input level:+23dBu
*Maximum output level:+23dBu
*Input impedance: balanced 20k Ω, unbalanced 10KHz
*Output impedance: balanced 200 Ω, unbalanced 100 Ω?
*Slope: ± 3%
*Octave frequency: 1/3 octave frequency
*Gain range: ≥ ± 6dB
2、 Acoustic Calculation of Sound Amplification System
1. Calculation of maximum power capacity and maximum voltage capacity
*Formula 1: Maximum voltage capacity V=√ Maximum power W × Load impedance Ω
*Formula 2: Maximum power capacity W=Maximum voltage V2 × Load impedance Ω
If the maximum continuous power (AES/ANSI) and indicated load impedance of a speaker are known, the maximum voltage of this speaker can be calculated. For example, the maximum power of speaker A is 600W RMS (ES/ANSI) and the impedance is 8 Ω. It is hoped that the maximum output voltage value of the amplifier can be set through the system's voltage limiter or speaker controller to protect speaker A. Relevant data can be input into formula one:
Maximum voltage capacity V=√ 600W × 8 Ω
=√ 4800
=69.28V
From this, it can be concluded that when a voltage of 69.28 V is applied to an 8 Ω load impedance, a maximum power of 600 WRMS can be generated. Therefore, we need to set the maximum output voltage value of the amplifier on the voltage limiter or speaker controller not to exceed 69.28 V in order to effectively protect speaker A from burning out.
2. Calculation of power amplifier voltage gain
*Formula 3: Voltage gain=Output voltage V/Input voltage V
The gain is determined by the relationship between the input and output of the audio circuit, and is expressed as a multiple (x) or in units of dB. If we want to know the gain of an amplifier (called voltage gain), we must know the input signal level and its corresponding output signal level. For example, it is known that the signal level input from the front-end of the system to amplifier A is 0.775V, and the output signal is 31V. By fitting the relevant data into formula three, the voltage gain of amplifier A can be obtained:
Voltage gain=output voltage V/input voltage V
=31V/0.775V
=40 x (times)
For example, if it is known that the signal level input from the front-end of the system to the B amplifier is 0.5V and the output signal is 20V, the voltage gain of the B amplifier can also be obtained by fitting the relevant data into formula three:
Voltage gain=output voltage V/input voltage V
=20V/0.5V
=40 x (times)
Note that from the above two examples, it can be seen that the voltage gain of amplifier A and amplifier B is the same, which is 40 x, so the magnitude of the voltage gain is independent of the size of the input signal.
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