The acoustic spectrum is extended by the low frequencies of 20Hz to the high frequencies of 20,000Hz. At low frequencies the sensitivity is degraded. This is the reason, that leads the discussion of the utilization of low frequency attribution. Defining the difference between these two frequency levels, so that we can direct it to the appropriate amplifier. Acoustic filters are fulfilled at various points in the audio system. The most known application is the baxandal filter to adjust the low & high tones, in addition to filtering the appropriate crossover. The proposed application is a simple filter to limit the acoustic region of 20-100Hz in the range of 20-20,000Hz.
Low pass filter - Subwoofer - Manufacture: Soulis Papanastasiou
The proposal will bring up the topic of active filters which will indirectly involve a discussion about the specifications of the appropriate loudspeaker for low frequencies, this is for the side of the opening circuit block / pre-amp. In addition, we will also place the loudspeaker for high frequencies in the closing circuit block / final amplifier / power-amp. Meanwhile, to bridge the two we will make a subwoofer, to provide dynamic effects.
1. Theoretical circuit
In that form appears the theoretical circuit circuit. In the first view we see three different circuits that are mainly produced round two operational amplifiers. These circuits are mixtures, amplifiers with variable assistance and variable filters. The final manufacture requires a catering circuit with a catering operational tendency equal to ± 12. operational amplifiers that are active elements for these circuits are dual operation types as TL082 and NE5532. These operational amplifiers belong to a family that is provided with transistors of the IFET field effect in their entries. Each member of the family allocates in the circuit bipolar transistors and field effects. These circuits can function in their high tendencies, because they use transistors with high tendencies. Also they have a high honor of the elevation rhythm (voltage change rate), low polarization current for the entries and are affected little by temperature. These operational amplifiers have a wide area gain bandwidth of 3MHz. Another important element for their choice is the large rejection of noise, when this is in the catering line.
The rejection price is greater than 80dB, the consumption is small, from 11 to 3 mA. They are internally sold briefly with eight pins and allocate two operational amplifiers, On the same line briefly 14 pins they combine four operational, In trade they are sold with the codes TL074, TL084 and TL064, In short with eight pins they are sold operational amplifiers TL061 TL071 kajTL081. In our manufacture we use TL082 which has two operations. The first operational of the TL082 it serves as an amplifier and is mixed for two channels, In its negative entry it has one small mixed with two resistances. The potentiometer in this step determines the help of the circuit. At this point of the left wing and the right channel of the preamplifier, they are added with two resistances. En operational continuity amplifies the signal with the help made depending on the price that has a potentiometer.
The runner place is comparable to the help of the circuit. The second operational amplifier is a filter of manufacture. The second class acoustic frequency filter and he is made with the material that surrounds the operational amplifier. The filter is a low part with a variable cut frequency. This frequency can be changed and takes a price from a very low frequency of 30Hz or still exceeding 150Hz. The cut frequency of the filter depends on the price that has the circuit elements. Changing the values of the elements we can have cut frequencies of 150Iz, 130Iz, J00Iz, 7Ïz, 6Íz even 3Íz, these prices they can be achieved with a simple rotation of the double potentiometer. The filter circuit has been made around one operational 'that has completed the TL082 which is a double operational amplifier. At the exit of the filter we will connect the cost plug where is connected the amplifier. At the exit of the circuit is presented, limited as its frequency width, the signal that we apply at the entrance of the circuit.
2. Manufacturing
Parts
| R1 = 39 Kohm | R2 = 39 Kohm |
|-----------------|-----------------|
| R3 = 47 Kohm | R4 = 10 Ohm |
| R5 = 22 Kohm | R6 = 4,7 Kohm |
| R7 = 22 Kohm | R8 = 4,7 Kohm |
| R9 = 10 Ohm | R10 = 220 Ohm |
| C1 = 39 pF | C2 = 0.1 uF |
| C3 = 0.1 uF | C4 = 0.2 uF |
| C5 = 0.4 uF | C6 = 0.1 uF |
| C7 = 0.1 uF | IC1 = TL064 |PCB
To make it, you need to print that appears in the form. In this case you will place the material according to the following form. Quite easy material can also be a certain error. With a little attention, you can avoid it. If they are presented with a difference malfunction, you carefully check the circuit. The circuit, as we said, is a filter and they should use precision and good quality materials, especially for capacitors. The filter capacitor will have a tolerance of 5%. Of course, manufacturing will also work with low quality materials, the test of manufacturing can be with an acoustic signal generator We apply the generator at the entrance to manufacturing and we measure with a voltmeter the tendency at the exit of the filter. If we change the potentiometer and change the tendency, then everything will be fine.