Linear Phase Response From 3-Way Crossover Circuit

Figure 1 

The circuit was designed to produce a 3-way crossover circuit that will produce a linear phase response within the filters included in the circuit.

• Linear Phase – a property of a filter where the phase response of the filter is a linear function of frequency and its system has the property of the true time delay
• Crossover – an external electronic signal processor that functions as a filter by limiting or blocking some range of frequencies sent to a speaker while allowing other frequencies to pass with little or no effect
• TL071 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption
• NE5532 – an internally compensated low noise dual operational amplifier with features such as full power bandwidth up to 140 KHz, input noise voltage of 8 nV, common mode rejection ratio, 9 V/us slew rate, high DC voltage gain, 32 V peak to peak voltage swing, wide supply voltage range from 3 V to 12 V, unity gain bandwidth at 10 MHz, and internal frequency compensation

In common crossover networks, there are problems that are being encountered which pertain mostly to the filters. The delay in the signal is usually caused by the low pass filter while the pre-ahead in the signal is caused by the high pass filter. Because of this, the cross frequency is creating some problems such as denial of the signals from the two filters, axial influence in the change of phase between the filters, and the frequency dependency of the axial diagram. These problems can be resolved by the use of crossover circuit.

The crossover circuit will try to produce a linear phase by using a low pass circuit with the aid of a time delay circuit which will create an output signal with features from low pass filter. The time delay can be altered and will not be constant throughout the region of the frequencies. There will be no difference in the two output signals or in the cross frequency. The crossover circuit is made up of two low pass filters of fourth order with -24dB/oct. One low pass filter is used for low frequency which has delay time T1 that imports low frequencies in LPF1. The other low pass filter is for high frequency signals, which has T2 delay time that imports low frequencies of LPF2 that occurs in the region of mi frequencies.

The presence of IC7A-B is to remove the signal that comes from the low pass filter, from the signal that has encountered a delay. This will cause a signal to have the same traits as the signal that passed from a low pass filter. The signal and loudspeaker level will be adjusted by the presence of a trimmer in the output line. The supply of the circuit comes from the stabilized voltage of 15V.

The uses of crossover circuits, especially the 3-way type, are widely seen in car stereos and equalizers with 3 channels. It can also be used in hi-fi systems with digital analyzers and equalizers and can be integrated with subwoofers. Other use of the crossover circuit is fo bass boosting and in autosound systems.

Source:users.otenet.gr/~athsam/3way_active_crossover_with_linear_phase_eng.htm