Some considerations for using the equalizer to change the audio signal

Think twice before taking the risk of using an equalizer to change the audio signal. Excessive use of corrections can have both advantages and disadvantages to the overall listening experience of the audience. The equalizer is not magical and incredible. It has many shortcomings and may have a deeper impact on sound.
Insufficient to correct, the equalizer was invented in the 1830s to correct the lack of sound; its main use was in Hollywood studios. Thanks to the support of an equalizer, now known as a fidelity filter, it has achieved good results in long-range amplification, which helps to promote its application and lead to later abuse. Since several generations of sound engineers are ignorant or completely ignorant of the effects of the equalizer on the sound, it is not surprising that the equalizer is used in such a situation and the resulting sound results are unsatisfactory.
The equalizer is used to mix the mixer input channels and wiring devices, for example on an output line to the speaker. Although the use of an equalizer in the microphone input channel allows us to recall the method of shaping the sound of the speaker or the sound of the instrument, the often overlooked question is whether the need for an equalizer may be a sign of error in the rest of the chain.
Equalization may be used to compensate for problems in audio link or speaker audio characteristics, in microphone selection or studio acoustic effects. It may even appear in studios with perfect acoustics, the latest speakers and the best microphones.
The use of an equalizer in the output channel to the speaker is a particularly interesting situation, as it is easy for people to misunderstand that all improper room acoustics and speaker reverberation problems can be solved.
The parametric equalizer and the graphic equalizer currently use two equalizers: the parametric and graphical equalizer graph 1 octave equalizer measurement calibration characteristic. The upper curve is the total response of three filters set at +6 dB and center frequencies of 630, 250 and 2500 Hz; the curve is the same doubling filter set at +2 dB. The parametric equalizer is capable of correcting the sound signal while independently controlling the filtering frequency, bandwidth and amplitude gain or attenuation. The frequency and peak amplitude or valley in each frequency range can be adjusted continuously or step by step using potentiometers and switches. The operator can adjust over a 20:1 frequency range while adjusting the sharpness or peak bandwidth, known as the quality factor (Q value), which is 0.29 to 5.0. Typically, the highest and lowest frequency ranges can be switched from peak to flat.
When such an equalizer is used to correct for insufficient acoustic characteristics or speaker reverberation characteristics, the operator may set the calibrator subjectively "through the human ear" or objectively using an audio analyzer. The microphone of the analyzer acts on the sound wave at the measurement position, and the calibration pattern shape of the calibrator is set to be opposite to the measured shape, so that the generated characteristic curve is as linear as possible. But all of this only applies to one point in space.
Since the operator's ear and the analyzer's microphone record the response characteristics of the speaker at one location, this can be problematic when the operator moves to another location. All settings of the equalizer at a certain location are not suitable for any position except where the microphone is placed. Furthermore, considering the complexity of the sound field in terms of acoustic standing waves and indoor resonance modes, and the ratio of direct and reflected sound waves in a more or less diffuse acoustic space, it is easy to understand that a slightly improved response is produced compared to a position. And the balance of the problematic results in all other nearby locations is not as good as the equilibrium. The human ear separated by the skull (average distance 19 cm) is very sensitive to the sound wave diffraction around the head, allowing us to feel the direction, intensity and time difference of the direct and reflected arrival sound waves. This is the "binaural" hearing.
Unwanted effects, in all cases except the use of the emulation head (the precise position where the microphone is placed in the left and right ears), due to the subjective nature of the auditory, the monophonic microphone even coincides with the stereo microphone that will feed the analyzer and be heard by the listener Completely different objective data. Figure 2 shows the measurement calibration curve for the 1/3 octave equalizers set at +2, +4, +6, +8, +10, and +12dB, respectively.
However, even with a simulation head and a measurement method with good subjective sensory correction, it is worth remembering that depending on the type of equalizer, any correction in one frequency range may be in a more or less wide range. Lead to undesired effects. This is illustrated in Figures 1 and 2. Obviously, the multiplier equalizer (Fig. 1) has much wider correction characteristics than the 1/3 octave equalizer (Fig. 2). This is determined by the characteristics of the equalizer.
However, even if the 1/3 octave equalizer has a fairly narrow characteristic when the calibrator is set to the highest position (+12 or +10 dB), they will have wider characteristics at +4 dB.

Therefore, it is very important to balance with a calm mind, as rational as possible and logically.