The role of the system

1. Mixer: The mixer is mainly used in the sound system to deal with the signal source: the microphone is weak signal amplification, impedance matching for a variety of different sources, the corresponding tone modification and integrated control. In the professional recording and stage performances, the mixer also has multiple marshalling output, digital format conversion, audio and video positioning editing and other functions.

A high-quality mixer, the basic technical specifications of the indicators should reach the following parameters:

* Total noise: -86.5dBu (20Hz ~ 20kHz)

* Total harmonic distortion THD: <0.0007% (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 terminals)　　

* Common mode rejection ratio CMR:> 90dB @ 1KHz

* Maximum input level: + 22dBu

* The maximum output level of the main output: + 28dBu

* Other output maximum level: + 22dBu

* Microphone input impedance: 1.3kΩ

* Line input impedance: 10kΩ

* Output impedance: 120Ω　　

2. Equalizer

Due to the resonance characteristics of the sound field, the sound absorption coefficient of the sound-absorbing material is different from that of the sound frequency, and the frequency response characteristic of the speaker is not uniform, there is a problem that some of the frequency sounds are too strong and some frequencies are insufficient. But the general mixer on the equalizer only high frequency, intermediate frequency, low frequency three frequency electrical signal were adjusted, not up to the fine frequency balance. Equalizer function is used to adjust the various frequency components of the electrical signal amplification, by a variety of different frequency of the electrical signal to compensate for the speaker and sound field defects, compensation and modification of various sound sources and other special effects (frequency balanced).

Equalizer in accordance with the different circuits, mainly divided into two types of equalizer and parametric equalizer, and graphic equalizer simple structure, intuitive and clear, widely used in professional audio.

Graphic equalizer, also known as chart equalizer, through the panel on the distribution of push and pull keys, can be intuitively reflected in the call out of the equilibrium compensation curve, the frequency of the upgrade and attenuation at a glance. Graphic equalizer using a constant Q-＆#118alue technology, each frequency is equipped with a push-pull potentiometer, regardless of the upgrade or attenuation of a frequency, the filter band bandwidth is always the same.

Commonly used professional graphic equalizer 20Hz ~ 20kHz signal is divided into 10, 15, 27, 31 to adjust. Users can choose different segments according to different requirements of the icon equalizer. In general, the frequency points of the 10-band equalizer are distributed at octave intervals and are used in general. The 15-band equalizer is distributed at 2/3 octave intervals and is used in professional sound reinforcement. / 3 octave interval distribution, most of the need for fine compensation in the use of occasions.

A high-quality equalizer, the basic technical specifications of the indicators should reach the following parameters:

* 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 20kΩ, non-balanced 10KHz

* Output impedance: balanced 200Ω, non-balanced 100?

* Slope: ± 3%

* Octave: 1/3 octave

* Gain range: ≥ ± 6dB

Second, the sound reinforcement system sound calculation

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 you know the maximum continuous power of a speaker (AES / ANSI) and the indicated load impedance, you can calculate the maximum voltage of the speaker, for example, the maximum power of the A speaker is 600W RMS (ES / ANSI), the impedance is 8Ω, hope Through the system of the pressure limiter or speaker controller set the maximum output voltage of the amplifier, the A speaker to protect the relevant data into the formula 1:

Maximum voltage capacity V = √600W × 8Ω

= √4800

= 69.28V

This results in a 69.28 V voltage applied to the 8Ω load impedance, which can produce a maximum power of 600WRMS. Therefore, we have to set the maximum output voltage on the compressor or speaker controller to exceed 69.28 V to effectively protect A The speaker will not burn.

2. Calculation of power amplifier gain

* Formula 3: Voltage Gain = Output Voltage V / Input Voltage V

The gain is determined by the relationship between the input and the output of the audio circuit. The gain is expressed as a multiple (×), or expressed in units of dB. If we want to know the gain of a amplifier (called the voltage gain), it must know that the input signal Flatten the corresponding output signal level. For example, it is known that the signal level from the system preamplifier to the A amplifier is 0.775V, the output signal is 31V, the relevant data into the formula three can know the A gain voltage gain:

Voltage gain = output voltage V / input voltage V

= 31V / 0.775V

= 40 × (times)

Another example is known from the system before the input to the B amplifier signal level is 0.5V, the output signal is 20V, the relevant data into the formula three can also be known B power amplifier voltage gain:

Voltage gain = output voltage V / input voltage V

= 20V / 0.5V

= 40 × (times)

Note that from the above two cases can be seen A, B two amplifier power gain is the same as 40 ×, so the voltage gain size and the size of the input signal has nothing to do.