The frequency response is a two-dimensional graph showing how the signal is unevenly amplified depending on its frequency. If we talk about low-frequency amplifiers , that is, acoustic equipment, then the frequency response determines the naturalness and naturalness of sound reproduction.
Audio distortion is linear and non-linear. Nonlinear include a change in the shape of the output signal, and linear - gain unevenness while maintaining its shape.
The amplitude characteristic of the amplifier has a feature: divisions on the abscissa axis, on which the frequency scale is applied in the audible range, has a logarithmic graduation, the higher the frequency, the smaller the intervals between divisions. This display method is justified by the features of human hearing, which distinguishes modulations the less, the higher their tone.
An ideal frequency response would look like a straight horizontal line. But, as you know, to create an amplifier that absolutely evenly and equally reproduces the entire spectrum even on a relatively narrow range of audible sounds is almost impossible. It's all about the characteristics of the electronic components that make up the circuit (both amplifying, semiconductor or tube, and auxiliary, capacitors and inductances). Any transistor, microcircuit, or lamp has its own frequency response. Only careful adjustment provided by the design of the entire device can compensate for the imperfectness of the individual components. This can be achieved by the selection of parts, and deep negative feedback, reducing both linear and non-linear distortions.
Since the amplitude-frequency characteristic cannot be ideal, we can only talk about the extent to which it deviates from a line parallel to the abscissa axis. It is generally accepted that a change in the gain within three decibels for human hearing is uncritical, therefore, the
frequency range is defined as the interval between the intersection of a line lying 3 dB below the peak gain value (usually in the region of 1000 Hz) with the characteristic line at the so-called “end bends ". It should not be considered that the frequencies below and above the borders of the frequency range are “not passed”, they are just noticeably worse.
You can remove the frequency response of an amplifier using simple instruments (an oscilloscope and an audio frequency generator), or using an accurate voltmeter. For this, it is necessary to apply a signal of the same magnitude, for example, 200 mV, and different frequencies to the device input, and measure its output intensity by plotting the data on a graph. At radio plants, it is customary to regulate the frequency response uniformity using a special all-wave generator that feeds the entire range, and a meter that clearly shows a diagram on the screen. In production conditions, it turns out much faster to achieve results.
The speaker systems, which serve as a payload for the amplifier, in turn, have their own characteristics, and they are also far from ideal. In order to compensate for the total frequency response in the design of the amplifier, devices such as tone controls or multi-band equalizers are provided. Equipment of the Hi-End class does not have such settings, their amplitude-frequency characteristic is so carefully tuned and coordinated with the complete speakers that, in addition to the volume knob and the toggle switch, other control devices are not required.