Loudness Sound Circuit

A loudness sound circuit for power up bass and treeble frquency. A simple loudness sound approach to this problem can be done inserting a circuit in the preamplifier stage, capable of varying automatically the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels. In order to obtain a good audio reproduction at different listening levels, a different tone-controls setting should be necessary to suit the well known behaviour of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves. Fortunately, the human ear is not too critical, so a rather simple circuit can provide a satisfactory performance through a 40dB range. The loudness sound circuit is shown with SW1 in the “Control-flat” position, i.e. without the Automatic Loudness sound Control. In this position the loudness sound circuit acts as a linear preamplifier stage, with the voltage gain set by means of Trimmer R7.  C1 boosts the low frequencies and C4 boosts the higher ones. Maximum boost at low frequencies is limited by R2; R5 do the same at high frequencies. Switching SW1 in the opposite position the circuit becomes an Automatic Loudness sound Control and its frequency response varies in respect to the position of the control knob by the amount shown in the table below. Here is a schematic loudness sound circuit:

Simple Loudness Sound Circuit

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