The circuit was designed to create a classic electronic crossover circuit that will provide a 3-way output on all loudspeakers.
Terminology Electronic 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 effectTL071 – 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 consumptionTL074 – low noise JFET quad operational amplifier with features such as high slew rate, latch up free operation, compensated internal frequency, low harmonic distortion, protection from output short circuit, JFET input stage with high input impedance, low offset current and input bias, low noise, and wide common-mode and differential voltage range Circuit Explanation
The electronic crossover circuit separates the different parts of the frequency spectrum, being a part of the speaker design, and sends the frequency to each driver. It is traditionally implemented passively because it has no additional power except for the signal. It normally consists of resistors, capacitors, and inductors that are arranged in a network and placed in the speaker enclosure. There are three kinds of crossovers available in the market, the passive crossover which does not require power thus, making it easy to install; the active crossover which requires additional wiring for power and ground connections but provides more fine-tuning control and flexibility over the audio; and the in-line crossover that is connected before the amplifier to sharpen the sound of the speaker system that comes in a set of specific frequency.
This circuit consists of passive crossover circuit in all of the 3-way loudspeakers wherein a separate amplifier on the final stage is attached to each loudspeaker. In this 3-way loudspeaker system, six final amplifiers were utilized although this setup consumes more space allocation and more expensive from extra amplifiers. On the other hand, the addition of more amplifiers will result to a better quality of sound due to the replication of audio signal. This is one of the characteristics that a loudspeaker is rated, with the regulation of signal being made easier and thus, making it technically feasible in the market.
During the operation of the circuit, the audio signal originates from the output of the preamplifier which is fed to the input of operational amplifier IC1. The total signal level is being controlled by the logarithmic potentiometer. The IC1 can easily adjust to the input and separation of the circuits. The circuit that is designed in the region of IC2A and IC2B is forming a high pass band filter. It bears a magnitude of 24 dB per octave with a crossover frequency of 3.1 KHz that drives the high frequency loudspeaker. A high pass filter allows frequencies above the predetermined point to pass while reducing the amplitude of frequencies lower than the cutoff frequency. Conversely, the circuit that operates in the region of IC3C and IC3D forms a low pass filter that bears a magnitude of -24 dB per octave and drives the low frequency loudspeaker with a crossover frequency of 400 Hz. A low pass filter would allow frequencies below the cutoff to pass while attenuating the signal of higher frequencies. A band pass filter exists in the circuit composed of IC2C & IC2D representing high pass filter and IC3A & IC3B representing low pass filter. It drives the middle range loudspeaker with a crossover frequency between 400 Hz and 3.1 KHz. A band pass filter would allow frequencies within a certain range to pass while rolling off the frequencies outside that range.
The trimmers TR1, 2, & 3, is being utilized to modify the level of amplification. The type of loudspeakers can change the value of the crossover frequencies. As much as necessary, any measurement of values should result to a steeper slope of 24 dB per octave magnitude. The ideal resistors to be used in the circuit should be made of metal film with 1% of ¼ W while the capacitors are preferably made of Mylar, propylene, or MKT rated close enough to the theoretical value. The preferred op-amp used should have a high slew rate. In this way, the circuit desired for each channel can be achieved.
R2-4-10= 11Kohms (22K//22K)
R6-8-14= 28Kohms (56K//56K)
R11-12-13= 11Kohms (22K//22K)
R15-16-17= 28Kohms (56K//56K)
RV1= 47Kohms Log.
|TR1-2-3= 10Kohms trimmer
C1= 4.7uF 63V MKT
C2-3-4-7= 100nF 63V ceramic
C5-6-8-9= 3.3nF 63V*
C10= 220nF 63V*
C11-12-13-14= 10nF 63V*
C15-17= 6.6nF 63V (3.3//3.3nF)*
C16-20= 100nF 63V MKT
|C18= 680nF 63V MKT
C19-21= 3.3nF 63V*
C22-24= 20nF 63V (10//10nF)*
C23-25= 10nF 63V*
C26= 2.2uF 63V MKT
*are polycarbonet, polypropylen,
MKT and all resistors are
metal film 1% 1/4W
In the present world, where high performance sound systems are emerging, the electronic crossovers are very essential to eliminate the distortion related to the designs of full range crossovers where an absolute mixing of the whole backline of instruments for stage music is being used to reinforce sounds. An increased performance in the sound system is the main role of electronic crossovers by allowing the loudspeaker system to be constructed as a 2-way, 3-way, or 4-way sound system. Without the presence of a crossover, the subwoofer and midrange will duplicate several identical frequencies and will cause the subwoofer to be exhausted by putting up high notes. The same way will happen to tweeters due to the piling up of bass notes in audio lane.
Other usage of a 3-way electronic crossover can be seen in car equalizers with 3 stereo channels, in subwoofer integration with remote capability, in digital equalizers and analyzers, in hi-fi systems, in bass boosting applications, in autosound systems used by musicians, and other car audio functions.