Crossovers and Equalizers Basics
Signal Processing Makes Car Audio Systems Sound Better
Signal processing devices like equalizers and crossovers bring out musical details and deliver improved sound quality to the audio system.
Signal processing devices like equalizers and crossovers bring out musical details and deliver improved sound quality to the audio system.
What is a Signal Processor?
The term ‘signal processor’ describes a device that modifies the original audio signal with the goal of improving how it sounds when played through the vehicle’s audio system. Depending on the sound effect, filtering, or corrective action it provides, the signal processor may have a more specific name.
The two most common audio signal processing functions are:
1. Equalization
2. Crossover Filtering
Signal processors performing multiple functions are simply called a ‘processor.’
The two most common audio signal processing functions are:
1. Equalization
2. Crossover Filtering
Signal processors performing multiple functions are simply called a ‘processor.’
Processing in the Digital Domain - DSP
Digital Signal Processing (DSP) in car audio allows high speed and accurate adjustments, much like a small computer. DSP technology is found in many receivers, signal processors such as digital equalizers, and in DSP-based integration devices.
• Converting Signal - DSP devices in an analog audio signal path must use analog-to-digital (ADC) to convert analog audio into a digital signal and digital-to-analog converters (DAC) to convert the processed signal back to analog form before it can continue through the audio signal path. The advantage of controlling audio signals in the digital domain is that there are fewer unintended changes to the audio signal such as phase shifting or signal voltage loss, which is more likely to happen in an analog signal path.
• Converting Signal - DSP devices in an analog audio signal path must use analog-to-digital (ADC) to convert analog audio into a digital signal and digital-to-analog converters (DAC) to convert the processed signal back to analog form before it can continue through the audio signal path. The advantage of controlling audio signals in the digital domain is that there are fewer unintended changes to the audio signal such as phase shifting or signal voltage loss, which is more likely to happen in an analog signal path.
What is an Equalizer?
Equalizers adjust specific frequencies called ‘bands.’ Frequency bands are accentuated or suppressed to smooth out or correct peaks and valleys in the frequency response. This results in a more even, or flat, frequency response, which provides a more balanced and ‘natural’ sound. Humans typically identify a ‘great’ sounding audio system as those that provide an even balance of transitions from one frequency to another.
Equalizers have between 1 and 31 adjustments. The number of bands often indicates the type of equalization process – graphic or parametric.
• Graphic Equalization – This type of equalization has fixed frequencies with ‘boost’ or ‘cut’ adjustments in that specific band. Most graphic equalizers have at least 5 bands, but as many as 31 bands are used in 1/3 octave graphic equalizers. More bands provide greater control and correction of frequency peaks and valleys; however, more bands also make adjustments more complex.
• Parametric Equalization – The primary difference between parametric and graphic equalization is variable versus fixed frequency bands. The parametric frequency band starts with a ‘center frequency’ and can be varied above or below that frequency to correct very specific acoustic response anomalies. This variance directs the parametric adjustment to be made where it is needed in that specific range, rather than a fixed frequency chosen by the manufacturer. While parametric equalizers typically have fewer than 5 bands, this type of equalization can be more complicated since it is difficult to know which frequency is being adjusted. Use of a real time (frequency response) analyzer called an ‘RTA’ or computer-based parametric equalizer may help in managing parametric adjustments. Many professional installation shops provide audio system fine tuning services using an RTA.
Equalization Recommended Practice - Graphic or parametric equalizers both allow you to adjust by audio signals by increasing or decreasing frequencies. To improve sound quality, it is generally recommended to decrease/reduce dominant frequencies rather than increasing/boosting weak or absent frequencies. Filling in frequencies that are not well produced is better accomplished by adding an amplifier (or increasing amplification), upgrading speakers, or adding a subwoofer. These improvements will ensure the audio system is capable of producing the full frequency range with even balance.
Here are the three most common uses of equalizers in car audio systems:
1. Built-In to Receiver - Many receivers have an equalizer built in that provides adjustments beyond basic bass and treble to fine tune sound quality. Built-in equalization for receivers can be graphic (5-10 bands), parametric (3-5 bands), or both types selectable by the user. Many allow memory presets to store favorite settings.
2. Dedicated Preamp Equalizer - Preamp equalizers are separate from the receiver and may include additional signal processing functions that make it the main control for audio system tuning. Most preamp equalizers are installed in the trunk and have a dash-mounted controller. Other preamp equalizers may use a laptop computer to configure and are hidden away with a preset buttons accessible to the user to change the sound. Many preamp level signal processors with equalization and line output converter capabilities connect with the car’s speaker level audio signals to allow easier integration with amplifiers and speakers when retaining the factory stereo.
3. Built-In to an Amplifier - The most frequent built-in equalization use in amplifiers is ‘bass boost.’ This provides a single frequency of boost in the lowest region of the frequency band, but it should not be thought of as a substitute for a great subwoofer. Rather, bass boost is intended to be an enhancement for the subwoofer’s performance by adding additional character to deep bass notes.
Equalizers have between 1 and 31 adjustments. The number of bands often indicates the type of equalization process – graphic or parametric.
• Graphic Equalization – This type of equalization has fixed frequencies with ‘boost’ or ‘cut’ adjustments in that specific band. Most graphic equalizers have at least 5 bands, but as many as 31 bands are used in 1/3 octave graphic equalizers. More bands provide greater control and correction of frequency peaks and valleys; however, more bands also make adjustments more complex.
• Parametric Equalization – The primary difference between parametric and graphic equalization is variable versus fixed frequency bands. The parametric frequency band starts with a ‘center frequency’ and can be varied above or below that frequency to correct very specific acoustic response anomalies. This variance directs the parametric adjustment to be made where it is needed in that specific range, rather than a fixed frequency chosen by the manufacturer. While parametric equalizers typically have fewer than 5 bands, this type of equalization can be more complicated since it is difficult to know which frequency is being adjusted. Use of a real time (frequency response) analyzer called an ‘RTA’ or computer-based parametric equalizer may help in managing parametric adjustments. Many professional installation shops provide audio system fine tuning services using an RTA.
Equalization Recommended Practice - Graphic or parametric equalizers both allow you to adjust by audio signals by increasing or decreasing frequencies. To improve sound quality, it is generally recommended to decrease/reduce dominant frequencies rather than increasing/boosting weak or absent frequencies. Filling in frequencies that are not well produced is better accomplished by adding an amplifier (or increasing amplification), upgrading speakers, or adding a subwoofer. These improvements will ensure the audio system is capable of producing the full frequency range with even balance.
Here are the three most common uses of equalizers in car audio systems:
1. Built-In to Receiver - Many receivers have an equalizer built in that provides adjustments beyond basic bass and treble to fine tune sound quality. Built-in equalization for receivers can be graphic (5-10 bands), parametric (3-5 bands), or both types selectable by the user. Many allow memory presets to store favorite settings.
2. Dedicated Preamp Equalizer - Preamp equalizers are separate from the receiver and may include additional signal processing functions that make it the main control for audio system tuning. Most preamp equalizers are installed in the trunk and have a dash-mounted controller. Other preamp equalizers may use a laptop computer to configure and are hidden away with a preset buttons accessible to the user to change the sound. Many preamp level signal processors with equalization and line output converter capabilities connect with the car’s speaker level audio signals to allow easier integration with amplifiers and speakers when retaining the factory stereo.
3. Built-In to an Amplifier - The most frequent built-in equalization use in amplifiers is ‘bass boost.’ This provides a single frequency of boost in the lowest region of the frequency band, but it should not be thought of as a substitute for a great subwoofer. Rather, bass boost is intended to be an enhancement for the subwoofer’s performance by adding additional character to deep bass notes.
Design for Great Sound First and Use Signal Equalization for Fine Tuning
The overall audio system design is important to ensure great sound. Check tips provided in Category Guides and other Buying Guides to make sure all of your car audio product decisions for receiver, speakers and amplifiers are complimentary and consistent. After that, consider signal processing with equalization to enhance sound quality.
What is a Crossover?
Crossovers are filters that narrow the frequency range of the music sent to a speaker. The reason crossovers are necessary in a multi-speaker audio system is that no single speaker is capable of producing the full range of audio frequencies from 20Hz-20KHz.
• Multiple Speaker Systems Need Filtering - Vehicle audio systems using multiple speakers to cover the 20-20KHz range should use crossovers to filter the signals sent to each speaker to ensure they are receiving only the frequencies they are capable of producing. This will improve the sound quality of each speaker.
o Subwoofers are intended to play low (bass) frequencies. Thus, mid to high frequencies should be filtered out for the subwoofer.
o Tweeters are intended to play high frequencies. Thus, low to mid frequencies should be filtered out for tweeters.
o Midrange speakers cover a wide range of frequencies; however they do not play extremely low or high frequency ranges. Thus, very low and very high frequencies should be filtered out for midrange speakers.
• Filter Points - Most subwoofers have a crossover point at 100Hz and below. Most tweeters have a crossover point at 3-5KHz and above. Midrange speakers cover roughly 100Hz-3KHz. These crossover points are general starting points and can be adjusted up or down to fine tune specific speaker combinations.
Crossovers are classified as High Pass, Low Pass or Band Pass:
• High Pass – In a high pass crossover, only frequencies at or above the crossover point are allowed to pass through to the speakers. Frequencies below the crossover point are filtered out.
• Low Pass – In a low pass crossover, only frequencies at or below the crossover point are allowed to pass through to the speakers. Frequencies above the crossover point are filtered out.
• Band Pass –A band-pass crossover combines high pass and low pass filters to apply two crossover frequencies. The frequencies between the two crossover points are allowed to pass through the filter to the speakers.
o Band pass crossovers can originate from a single device with high pass and low pass filters applied to a specific channel. Preamp level signal processors often have this band pass filter feature in their crossover selection.
o Band pass crossovers can also be applied individually, with a high pass filter from one device (such as a receiver) and a low pass filter from another (such as the amplifier) when both filters are applied to the same channel(s).
• Example 1: Combine a built-in 100Hz high pass amplifier crossover with an externally mounted passive crossover (included with component speakers) that provides a low pass crossover to the midrange, typically around 3KHz. The result is a band pass filter on the midrange speaker with 100Hz to 3KHz coverage.
• Example 2: Combine a built in 100Hz low pass ‘SUB OUT’ receiver crossover with a built-in 25Hz high pass (subsonic) filter in an amplifier and the result is a band pass response for a subwoofer. High frequencies from the low pass crossover point are filtered out above 100Hz and subsonic frequencies below 25Hz are filtered out from the high pass crossover point.
• Slope – The rate at which frequencies are filtered is called the slope or ‘roll-off.’ Slope rates are expressed in decibels per octave (dB/oct) and are in increments of 6dB. Higher slopes mean greater attenuation at neighboring frequencies.
o Common slopes range from 6, 12 or 18dB/octave and 24dB/octave. Crossovers with slopes exceeding 24dB/octave are generally features of high-end DSP based signal processors that include equalization and time correction.
• Active versus Passive – Active crossovers are used in the preamp signal path before amplifiers. Passive crossovers are used after amplifiers and before the speakers and require no DC electrical power, only a speaker level audio signal. This is the difference between active versus passive crossovers.
o Active Crossover – Active crossovers are built into receivers, stand-alone preamp level signal processors, or amplifier(s). In all cases, the filtering is done before the signal is amplified. The benefit of this type of crossover is that there is virtually no loss of power between the amplifier and speaker. Each amplifier channel becomes dedicated to a specific frequency range when using active crossovers, so additional channels may be required to connect all speakers in the system.
o Passive Crossover – Passive crossovers connect after the amplifier with inductors, non-polar capacitors, and resistors in specific combinations. Passive crossovers are often included with premium coaxial or component speakers to separate the frequencies between the midrange driver and the tweeter, which improves sound and adds power handling to each speaker.
• Multiple Speaker Systems Need Filtering - Vehicle audio systems using multiple speakers to cover the 20-20KHz range should use crossovers to filter the signals sent to each speaker to ensure they are receiving only the frequencies they are capable of producing. This will improve the sound quality of each speaker.
o Subwoofers are intended to play low (bass) frequencies. Thus, mid to high frequencies should be filtered out for the subwoofer.
o Tweeters are intended to play high frequencies. Thus, low to mid frequencies should be filtered out for tweeters.
o Midrange speakers cover a wide range of frequencies; however they do not play extremely low or high frequency ranges. Thus, very low and very high frequencies should be filtered out for midrange speakers.
• Filter Points - Most subwoofers have a crossover point at 100Hz and below. Most tweeters have a crossover point at 3-5KHz and above. Midrange speakers cover roughly 100Hz-3KHz. These crossover points are general starting points and can be adjusted up or down to fine tune specific speaker combinations.
Crossovers are classified as High Pass, Low Pass or Band Pass:
• High Pass – In a high pass crossover, only frequencies at or above the crossover point are allowed to pass through to the speakers. Frequencies below the crossover point are filtered out.
• Low Pass – In a low pass crossover, only frequencies at or below the crossover point are allowed to pass through to the speakers. Frequencies above the crossover point are filtered out.
• Band Pass –A band-pass crossover combines high pass and low pass filters to apply two crossover frequencies. The frequencies between the two crossover points are allowed to pass through the filter to the speakers.
o Band pass crossovers can originate from a single device with high pass and low pass filters applied to a specific channel. Preamp level signal processors often have this band pass filter feature in their crossover selection.
o Band pass crossovers can also be applied individually, with a high pass filter from one device (such as a receiver) and a low pass filter from another (such as the amplifier) when both filters are applied to the same channel(s).
• Example 1: Combine a built-in 100Hz high pass amplifier crossover with an externally mounted passive crossover (included with component speakers) that provides a low pass crossover to the midrange, typically around 3KHz. The result is a band pass filter on the midrange speaker with 100Hz to 3KHz coverage.
• Example 2: Combine a built in 100Hz low pass ‘SUB OUT’ receiver crossover with a built-in 25Hz high pass (subsonic) filter in an amplifier and the result is a band pass response for a subwoofer. High frequencies from the low pass crossover point are filtered out above 100Hz and subsonic frequencies below 25Hz are filtered out from the high pass crossover point.
• Slope – The rate at which frequencies are filtered is called the slope or ‘roll-off.’ Slope rates are expressed in decibels per octave (dB/oct) and are in increments of 6dB. Higher slopes mean greater attenuation at neighboring frequencies.
o Common slopes range from 6, 12 or 18dB/octave and 24dB/octave. Crossovers with slopes exceeding 24dB/octave are generally features of high-end DSP based signal processors that include equalization and time correction.
• Active versus Passive – Active crossovers are used in the preamp signal path before amplifiers. Passive crossovers are used after amplifiers and before the speakers and require no DC electrical power, only a speaker level audio signal. This is the difference between active versus passive crossovers.
o Active Crossover – Active crossovers are built into receivers, stand-alone preamp level signal processors, or amplifier(s). In all cases, the filtering is done before the signal is amplified. The benefit of this type of crossover is that there is virtually no loss of power between the amplifier and speaker. Each amplifier channel becomes dedicated to a specific frequency range when using active crossovers, so additional channels may be required to connect all speakers in the system.
o Passive Crossover – Passive crossovers connect after the amplifier with inductors, non-polar capacitors, and resistors in specific combinations. Passive crossovers are often included with premium coaxial or component speakers to separate the frequencies between the midrange driver and the tweeter, which improves sound and adds power handling to each speaker.
When to Consider Professional Installation and Audio System Tuning
Vehicles are complex machines. Before attempting any DIY installation, assess your comfort level with the installation of electronics and mechanics of your vehicle.
Consider a professional installer if:
1. You are not comfortable disassembling vehicle interior panels.
2. You do not have a suitable work area available.
3. You do not have the recommended tools for the job.
4. You do not have the necessary installation accessories specific to your vehicle year/make/model.
Many independent retail installation shops welcome jobs with products purchased on Amazon.com. Professional installers can also provide many of the installation accessories you need for jobs that are covered in this guide. They can also provide expert tuning of signal processors to bring the enhanced sound quality out of your car audio system. Always look for a Mobile Electronics Certified Professional (MECP) installation technician to handle your most challenging installation needs.
Want to purchase installation now? Find an InstallerNet card on Amazon.com that corresponds to your job type.
Consider a professional installer if:
1. You are not comfortable disassembling vehicle interior panels.
2. You do not have a suitable work area available.
3. You do not have the recommended tools for the job.
4. You do not have the necessary installation accessories specific to your vehicle year/make/model.
Many independent retail installation shops welcome jobs with products purchased on Amazon.com. Professional installers can also provide many of the installation accessories you need for jobs that are covered in this guide. They can also provide expert tuning of signal processors to bring the enhanced sound quality out of your car audio system. Always look for a Mobile Electronics Certified Professional (MECP) installation technician to handle your most challenging installation needs.
Want to purchase installation now? Find an InstallerNet card on Amazon.com that corresponds to your job type.
THANKS: amazon.com