Acoustic crossovers are electronic devices that receive one input signal and create two or three output signals consisting of separated high, medium and low frequency bands. Different ranges are provided by different speakers or “drivers” in the sound system: woofers and subwoofers. Without a crossover, a random breakdown of sound occurs. In them, the high-pass filter blocks the lows, but transmits high-frequency notes to the tweeter, while the low-pass filter blocks the highs and passes low-frequency notes to the subwoofer.
Component sound system
Crossover “networks” of coaxial multi-band car speakers are typically built into speakers and consist of small electrical components such as coils or capacitors. Crossovers for three-way systems that use tweeters, mid-range drivers and subwoofers include, in addition to high and low-pass filters, “pass-band” filters that reproduce frequencies between two points, using both high-frequency and low-frequency in the same network. For this, there may be a mid-range driver from only 100 Hz to 2500 Hz.
There are two main types of acoustic crossovers: active and passive. Passive ones do not need power to filter the signal. Active ones require a power and ground connection, but give much greater flexibility and precise control over user music.
Active audio system
The sound system is called “active” when each driver, tweeter, woofer has its own gain channel. This significantly increases the available power, dynamic range and tonal control of the system across the entire audio spectrum. The acoustic active crossover connects between the receiver and the amplifier and cuts off unnecessary frequencies, so it can only focus on the frequencies that the user wants to hear.
They usually have volume controls on each channel, so you can keep all the “voices” from different drivers in balance. Some crossovers include other audio processing features such as leveling to further customize the system. The only potential drawback of this type of crossover is that it requires + 12 V, grounding and plug-in connections. This presents a greater problem for installation and configuration than a passive device.
Passive acoustic devices
Acoustic passive crossover is not connected to a power source. There are two types of passive crossovers: component crossovers connecting between the amplifier and speakers, and built-in, which are located between the receiver and amplifier.
Component Passive transitions of components into the signal path come after the amplifier. These are small networks of capacitors and coils that are usually installed next to loudspeakers. Component speakers come with crossovers installed for optimal performance. They are easy to install and configure. The full-range signal leaves the amplifier and passes to a passive crossover, which divides it into two parts and sends high notes to the tweeter, and medium and low notes to the low-frequency speaker. Most passive component crossovers have additional settings that turn off the tweeter if the sound seems too loud for the subwoofer.
In addition to passive crossovers that operate on speaker signals and are connected between the amplifier and speaker components, there are also built-in acoustic car crossovers installed in front of the amplifier. They look like small cylinders with RCA connectors at each end and just plug into the inputs. Built-in crossovers do not lose energy, like high frequencies for a subwoofer. Installing an integrated crossover is an excellent and inexpensive way to improve the sound of the center, especially in a component speaker system.
Principles of using car audio
To understand what a crossover is and whether a sound need really needs one or more crossovers, it is important to first understand some very simple principles for using a car crossover. The main idea is that music consists of sound frequencies that control the entire gamut of human hearing, but individual sources are better at creating specific frequencies than others.
Tweeters are designed to recreate high frequencies, woofers are designed to reproduce low frequencies, etc. The main goal is to split the music into composite frequencies and transmit it to specific speakers to achieve higher fidelity audio. By making sure that only the right frequencies reach the classic speakers, you can more effectively reduce distortion and improve the sound quality in the car audio system.
Installing passive acoustic crossovers is a relatively easy task, as it provides crossover wiring between the amplifier and speakers. For example, you can connect a passive crossover to the amplifier output, and then connect the tweeter output to the tweeter and the subwoofer output to the subwoofer.
Installing an active car audio crossover will usually be a more complicated procedure. The main problem is that power is required for active crossovers, so you will need to lay power and ground wires for each device. If an amplifier is already installed, installing an active crossover will be easier. In fact, grounding it in the same place where the amplifier is grounded will help prevent annoying interference in the ground loop.
Crossover Classification
Acoustic crossovers can be classified by the number of bands into which the sound spectrum is divided. Two-way splits the audio spectrum into two parts and sends information to various types of drivers. Three-way divides the sound spectrum into three parts and so on. The crossover can also be described by the point where the steep cut begins. It usually refers to the frequency with which the descent begins. On both sides, both drivers will have 6 dB at the intersection point.
Terms often used to describe the crossover slope include 6 dB / octave, 12 dB / octave, 18 dB / octave, or 24 dB / octave. The slope of the crossover to which these terms refer. When changing one octave, the 6 dB / octave crossover will have an output that is 6 dB below the starting point; 12 dB / octave will have a 12 dB output. Another set of terms that are often used to describe the slope of the crossover is 1st order, 2nd order, 3rd order, and 4th order.
These terms are derived from among the components necessary to create the described slope. A 1st order crossover uses 1 component and will give approximately 6 dB / octave. A 2nd order crossover uses 2 components and will give approximately 12 dB / octave, etc.
Center speaker components
If it is difficult to find a value that is not more than 10% of the desired sound, carry out the adjustment. Here are some tips for working with various components:
- Capacitors: combine two capacitors, connect them in parallel. Using them in this way, you can simply add two values together to get a joint equivalent capacity.
- Resistors: connect two resistors in series to provide a joint resistance equivalent to the total value. The power rating on both must be high in order to meet the requirements of the system.
- Inductors: if you do not need to use several inductors, you can buy an oversized one, and then unwind the coils until the desired value is reached. The disadvantage of this method is that it is necessary to use a certain type of inductance meter.
Frequency Range Definition
Tuning the speaker crossover is to adjust the frequencies correctly. To determine the acceptable range that is used for the settings, you need to know the data for both the speakers and the subwoofer. The purchased speaker package always contains a guide for the settings that you must use.
In other cases, the following rules apply. The highest frequency that the subwoofer is capable of working with should be used for crossover settings. The lowest frequency that the speaker can handle must be set to the crossover.
For example, for the subwoofer frequency range of 20-130 Hz and the center speaker frequency range of 70-20 000 Hz, the allowable crossover setting range for the main speaker will be 70-130 Hz. This means that you can apply a setting of 70, 80, 90, etc., up to 130 Hz for the main speaker. If used above or below the specified size, then frequencies outside the range will not be reproduced by either the subwoofer or the corresponding speaker.
Main building blocks
In a car audio system, large pendant capacitors are used to prevent the lights from fading when playing loud bass notes. They achieve this by providing the amplifier with a quick boost of power. Capacitors for speaker crossovers have a high “impedance”, commonly referred to as reactive for low frequency signals.
For capacitors, three main specifications are used:
- The maximum voltage at which it is not subjected to dialectic breakdown. This breakdown occurs when the electric field between the two plates of the capacitor becomes sufficient to polarize the dialectic, thereby turning it into a conductor. When this happens, the capacitor will become hot and may explode.
- The capacitance of capacitors is usually measured in microfarads - mF or uF or (Greek letter mu) F. The microfarad is 1/1 000 000 or 1 × 10 -6 Farads. And also used Picofarads, which is 1/1 000 000 or 1 × 10 -6 microfarads (1 × 10 -12 Farads).
- Tolerance This is an acceptable variation of meaning. For example, a 47 mF capacitor with a range of -20% / + 80% will have a capacitance of 37.6 to 84.6 mF. In audio systems, a capacitor is usually connected in series with each “high-frequency” speaker to act as a high-pass filter.
System impedance calculation
If all the speakers are connected in parallel and have the same impedance, then the calculation of the acoustic crossover is easy to perform. Just divide the impedance by the number of columns in parallel.
Example 1: Four 8-ohm speakers, parallel connection: 8/4 = 2 ohms. Example 2: Two 4 ohm speakers, parallel circuit: 4/2 = 2 ohms.
To calculate speakers connected in parallel but with different impedance, the following formula is used:
R total = 1 / (1 / r1 + 1 / r2 + .....).
Actually, the exact calculation of an audio system is a very complex empirical process. To simplify it, online calculators for calculating the crossover of speakers are widely represented on the Internet, for example, a separate calculator for 2, 3 and 4 speakers connected in parallel, as well as calculators that can be used for more complex serial / parallel configurations. To do this, you need to enter the impedance of each speaker in the white squares of the corresponding calculator. The total impedance for speakers connected in parallel will be determined. And also for each speaker the percentage is calculated.
The display will show how the power output of the amplifier is distributed between the speakers. When used with different impedances, power sharing will be considered.
If there was one driver that could easily and accurately reproduce the entire spectrum of audio, the use of a crossover would not be required. The main reason is that it usually requires several drivers to cover the entire spectrum of sound. It is impossible to make a driver capable of simultaneously producing both high and low frequencies. Different types of drivers are designed to work well in different ranges. Using a crossover helps coordinate the work of different drivers.