Homemade subwoofer playback system 02

The left and right channel signals taken from the speaker output terminals of the original audio equipment are buffered by Rl, RZ mixing stations and ICla and then sent to
high and low pass filters .
    The filter uses a low-noise and high-impedance operational amplifier TJ.D82 port lC lb etc. at the input stage of the junction field effect transistor to form a low-pass filter with a cut-off frequency of 20Hz. In this way, a band like Figure 9-23
is obtained at the output end of the buffer IC2b.
Pass filter characteristics, frequency range is 20Hz ~ 150Hz. The mother power amplifier uses
two integrated power amplifiers LM1875 with overheating and overload protection, forming a BTI. The output power of the amplifier
is nearly low, which is sufficient for high-power amplification of subwoofers. RP is used for subwoofer volume
adjustment.
    This power amplifier is specially designed to amplify ultra-low frequency signals from 20Hz to 150Hz and can
be connected to any type of subwoofer.
    It is generally believed that the low-frequency reproduction limit of the phase inverter box is better than that of the airtight box, but in actual production, the phase
inverter box has extremely strict requirements on the Q value of the speaker; if the calculation, production, and debugging are slightly improper, the reproduction limit frequency will be Cannot meet
the requirements. Without the necessary acoustic testing methods under amateur conditions, the advantages of the phase inverter box would be out of reach. 6 Relatively speaking, the
Q value requirements of the airtight box are not strict, and the impact of calculation, production, and debugging errors on the performance is far greater than that of the inverter box. The phase box should be small and its transient response
should be better than that of the phase inverter box. The main disadvantage of the closed box is that its frequency response begins to decrease from higher frequencies, but this shortcoming can be compensated for by the high and low pass filters
in Figure 9-23. Only signals between 20Hz and 50Hz can be played back. , the lower limit of playback of the sealed box can reach or exceed the level of the phase inverter box. A 10-inch, 70W domestic speaker with an impedance of 8n and a sealed box size of 510mm × 420mm × 260mm is used here , filled with sound-absorbing materials.