What Is A Speaker Crossover Network? (Active & Passive)


Whether we’re aware of them or not, crossover networks are used in nearly all our loudspeakers and play a major role in how we hear the speaker drivers.

What is a speaker crossover network? A speaker crossover is a network of filters that separate bands of frequencies of an input audio signal and outputs each band to the driver best-suited to reproduce it. For example, low-frequencies are sent to the woofer, mids are sent to the mid-range speaker and highs are sent to the tweeter.

In this in-depth article, we’ll discuss speaker crossovers in great detail. We’ll touch on the design and functionality of passive and active crossovers, and how they fit into speaker design.


What Is A Speaker Crossover?

Unfortunately, speaker drivers are pretty bad at producing the entire range of audible frequencies. Therefore, multiple speaker drivers are typically required to cover 20 Hz to 20,000 Hz.

In proper speaker designs, crossover networks effectively split up the full-range audio signal into smaller frequency bands that each speaker driver can accurately produce. They are, therefore, critical to proper speaker performance.

There are 3 types of filters that we’ll find in a speaker crossover network. They are:

  • Low-pass filter: a low-pass filter (also known as a high-cut filter) allows the low frequencies to pass unfiltered while it filters out or “cuts” the high frequencies.
  • High-pass filter: a high-pass filter (also known as a low-cut filter) allows the high frequencies to pass unfiltered while it filters out or “cuts” the low frequencies.
  • Band-pass filter: a band-pass filter can be thought of as a combination of a LPF and HPF. It allows a particular band of frequencies to pass by filtering out frequencies above the high point of the band and the frequencies below the low point of the band.

Related article on HPFs: What Is A Microphone High-Pass Filter And Why Use One?

There’s a lot to know about audio filters. So much so that they deserve multiple articles to themselves.

For this article, just know that they work to remove frequencies in the audio signal above and/or below certain cut-off points.

Multi-Driver Speakers

As mentioned, speakers nearly always require multiple drivers to produce the entire audible range of frequencies. This is the case with moving-coil dynamic speakers which make up the overwhelming majority of speakers on the market.

Each driver, unfortunately, has a limited frequency response. It can only produce a certain range of frequencies with the clarity, loudness and efficiency required of a loudspeaker.

So speakers are typically constructed with multiple drivers. They are known as:

  • 2-way speakers: these speakers have 2 drivers (typically a woofer and tweeter) and rely on a 2-way crossover (lows and highs).
  • 3-way speakers: these speakers have 3 drivers (typically a woofer, mid-range speaker and tweeter) and rely on a 3-way crossover (lows, mids and highs).
  • 4-way speakers: these speakers have 4 drivers (often a woofer, mid-range speaker, tweeter and super-tweeter) and rely on a 4-way crossover (lows, mids/low-mids, highs/high-mids, highs/super-highs)

So on and so forth…

Subwoofers are generally separate due to their special requirements (larger enclosures, additional amplification/power, room positioning, etc.). However, subwoofers also use crossovers in order to be driver only by the lowest frequencies of the audio signal.

To learn more about the different types of speaker drivers, check out my in-depth article Differences Between Mid-Range Speakers, Tweeters & Woofers

Why Are Speaker Crossover Networks Necessary?

A fair question to ask goes something along the lines of this:

“If the speaker’s drivers are only designed to produce a certain frequency band, why can’t we just send the full audio signal to them and allow them to only produce what they can?”

The answer to this question has to do with the efficiency and longevity of the speaker drivers as well as the overall frequency response of the speaker as a whole.

Let’s say that we have a 3-way speaker with no crossover whatsoever. Here are the issues that will likely surface:

Each driver will waste energy trying to reproduce frequencies it isn’t meant to handle.

This wasted energy makes the entire system less efficient and may even cause damage, which we’ll get to shortly.

The limits of the frequency response of each driver are likely to overlap somewhat with the adjacent driver.

For example, there will be an overlap between the upper range of the woofer’s frequency response and the lower range of the mid-range speaker’s frequency response. The same will be true of the mid-range speaker and the tweeter.

Note that if this is not the case, then the speaker will have inherent notches in its overall frequency response and will likely sound terrible.

Finally, the low-end energy of the audio signal could very well blow the tweeter driver at high enough levels. The excess wasted energy could heat up and melt the tweeter voice coil. Similarly, the over excursion caused by a high amplitude low-end frequency could damage the tweeter.

So, then, speaker crossovers are required for 3 big reasons:

  • To improve efficiency.
  • To avoid the overproduction of “in-between” frequencies.
  • To avoid damage to the smaller drivers.

I had once heard someone liken an audio crossover to a traffic cop and liked the analogy.

The crossover, like the traffic coordinator, sends frequencies to where they need to go. In doing so, it makes the system more efficient, avoids traffic jams at certain points within the frequency response and helps to prevent accidents from happening.


Active Vs. Passive Speaker Crossovers

Now that we understand what a speaker crossovers are, we can have a look at the different types.

Just like there are active and passive speakers, there are also active and passive speaker crossovers.

As you may suspect, active crossovers are used in active speakers and passive crossovers are used in passive speakers.

For more information on passive and active speakers, check out my article What Are The Differences Between Passive & Active Speakers?

So what’s the difference between active and passive crossovers? The following table will present a general overview before we compare and contrast:

Active CrossoversPassive Crossovers
Require external power to function.Do not require external power to function.
Deal with line level audio signals at their input.Deal with speaker level audio signals.
Filter before amplification. Each driver gets its own amplifier.Filter already-amplified signals. Rely on external amps.
Greater control over the volume of each band.No control over the volume of each band.

Power Requirements

Passive crossovers are made of passive electrical components (inductors, capacitors and resistors) and, therefore, do not require external power to function.

Active crossovers, on the other hand, have operational amplifier (op-amp) components that do require power to function properly. They also have the aforementioned inductors, capacitors and resistors.

Note that active speakers also require a separate power amp between each crossover audio band and the intended driver. These amps also require power.

Input Levels

Active crossovers are put between the audio source and the amplifiers or the active speaker. They, therefore, are designed to deal with line level audio at their inputs and in their circuits.

Simplified Active Speaker Signal Flow

The relatively low voltage of line level signals allows active crossovers to utilize op-amps in their design and to have less robust inductors, capacitors and resistors.

Passive crossovers, conversely, are designed to handle already-amplified speaker level audio at their inputs as they are put between the amplifier and the drivers of the passive speaker.

Simplified Passive Speaker Signal Flow

There are limitations to the power passive crossovers can handle.

The inductors are limited in the magnetic fields they produce. The capacitors have a maximum voltage they can handle. Passive crossover networks can overheat and fail if the speaker level signal is too great.

The Amplifier(s)

To continue with the statements above, passive crossovers are put after an amplifier in the signal chain while active crossovers are put before amplifiers in the signal chain.

The passive speaker relies on a power amplifier that boosts the entire audio signal before it gets to the crossover. As previously mentioned, this speaker level signal can be hard on the passive crossover. The passive crossover needs robust components to handle this strong signal.

Active crossover networks split the audio signal up into its bands before sending each band to its own dedicated amplifier. This means that the amplifiers will be more efficient and waste less energy by not amplifying frequencies that will not ultimately be reproduced by the driver.

Having individual amps allows more control over each of the frequency bands. It also means that if any of the bands clip, it will only affect the single driver.

Having amplifiers between the active crossover filters and the drivers also helps in simplifying the matching of impedance between the amps and drivers.

Passive crossover effectively puts inductors, capacitors and resistors between the amplifiers and the speaker drivers which will all play a role on the load impedance presented to the amplifier. This load may not always be constant.

On the other hand, any component that supplies gain (op-amps, for example) also introduce noise to the signal. Introducing noise to the signal before the power amplifiers makes the noise even worse. This is a con of active speakers.

Control

Passive crossover networks are designed to work at specific crossover points and are often made from specific speakers.

Active crossovers have more control. This control includes volume adjustments and even frequency adjustments to change the level and cutoff frequencies of the crossover bands. This allows them to be more universally used with speakers.


In-Line Crossovers

In-line crossovers are technically passive as well in the fact that they do not require power to function.

However, in-line crossovers are put in-line before the amplifier rather than between the amplifier and the speaker drivers.

These crossovers filter out the unnecessary frequencies from the audio before it reaches the amplifier and the speaker driver, thereby reducing the energy the amplifier would otherwise waste.

In-line crossovers are commonly used simply as low-pass filters that connect to subwoofer amplifiers.


DSP Active Crossovers

There are also DSP (Digital Signal Processing) crossovers on the market. These crossovers are inherently active since ADC and DAC (analog-to-digital converters and digital-to-analog converters) are necessary and require power.

With digital processing, we can have much more control over the limits and levels of the frequency bands of the crossover.


Pros & Cons Of Passive & Active Crossovers

At the risk of repeating myself, let’s go over all the pros and cons of passive crossovers and of active crossovers. We’ll begin with the passive designs.

Pros & Cons Of Passive Crossovers

Below is a list of the pros and cons of passive crossovers:

ProsCons
Simple (plug and play)Crossover interference (back EMF) with amplifier signal
Single speaker cable (per speaker)Loss of speaker damping and amp's direct control of driver especially near the crossover frequency
Single stereo ampHigher loading on amplifier with greater losses requiring higher wattage
Usually less expensiveUneven phase shifting between drivers with different impedances
Variable and nonlinear responses with changes in power and temperature
Higher THD and intermodulation distortion, interference patterns, amplitude irregularities, driver resonances, cone breakup, and degraded off-axis response
Greater probability of amplifier clipping and driver damage due to higher power and complex impedance loads.

Pros & Cons Of Active Crossovers

And now for the pros and cons of active crossovers:

ProsCons
Direct control of each driver by each amp channelInherently more complex
Simple and easier impedance loading on ampPotentially increased noise
No parasitic power lossesAt least twice the number of cables
No loss of damping (driver control)Requires multiples amps or amps with multiple channels
Less likelihood of clipping with clipping limited to single driverUsually more expensive
Consistent crossover behavior regardless of power level or signal content
Less loading on each amp with load divided among multiple amps
Less distortion
Highly flexible and adaptable especially with DSP technology

Which Speaker Crossover Type Is Better?

By the statements made above, we infer that active speaker crossovers are better performers.

Active crossovers (generally speaking) simply sound better and solve many of the issues inherent in passive crossovers. The only major downside is in the price which may or may not be a big deal to you.


Built-In & External Speaker Crossovers

The vast majority of multi-driver speakers on the market today (both active and passive) have built-in crossover networks.

However, there are plenty of scenarios that call for external standalone speaker crossovers, including:

  • Building a speaker ourselves with individual drivers, enclosure, crossover and amplifier(s).
  • Splitting audio before sending it to “regular” speakers and to a subwoofer.
  • Automobile audio.
  • Crossover-less multi-driver speakers.

Let’s now have a look at a few examples of speaker crossovers.


Speaker Crossover Examples

In this section, we’ll have a look at the following speaker crossovers:

Rane Commercial AC 23S

The Rane Commercial AC 23S (link to check the price at B&H Photo/Video) is an active rack-mountable crossover that can be configured as a stereo 2-way or 3-way, or as a mono 4-way or 5-way crossover.

Rane AC 23S
  • Active or passive: Active
  • Inputs: 2 balanced XLR (Impedance of 20 kΩ)
    • Left/Mono
    • Right/Omit
  • Outputs: 6 balanced XLR (Impedance of 200 Ω)
    • Left high
    • Left mid/low
    • Left low
    • Right high
    • Right mid/low
    • Right low
  • Crossover points:
    • 3-Way low-mid range: 70 Hz – 1 kHz (24 dB per octave)
    • 3-Way mid-high range: 190 Hz – 7 kHz (24 dB per octave)
    • 2-Way low-mid range: 190 Hz – 7 kHz (24 dB per octave)

Audiopipe CRX-203

The Audiopipe CRX-203 (link to check the price on Amazon) is a 2-way passive crossover network designed for car audio.

  • Active or passive: Passive
  • Inputs: 1 pair of gold-plated screw terminals (IN– and IN+)
  • Outputs: 2 pairs of gold-plate screw terminals
    • W– and W+ (woofer)
    • T– and T+ (tweeter)
  • Crossover point:
    • Woofer Frequency: 20Hz – 5.6kHz
    • Tweeter Frequency: 5kHz-20kHz
  • Maximum power handling: 300 watts per crossover (600 watts per pair)
  • RMS power handling: 150 watts per crossover (300 watts per pair)

Eminence PXB3

Eminence PXB3 (link to compare prices at Amazon and select retailers) is a passive 3-way crossover with crossover points at 500 Hz and 5,000 Hz.

Eminence PXB3
  • Active or passive: Passive
  • Inputs: 1 pair of terminals (IN+ and IN–)
  • Outputs: 3 pairs of terminals
    • M+ and M– (mid-range speaker)
    • W+ and W– (woofer)
    • T+ and T– (tweeter)
  • Crossover points:
    • Low-mid: 500 Hz
    • Mid-high: 5 kHz
  • RMS power handling: 400 watts

Note that, like the Audiopipe CRX-203, we can see the inductors and capacitors of the Eminence PXB3 on the circuit board.

SPL Crossover

The SPL Crossover (link to check the price at B&H Photo/Video) is an active, analog 2-way crossover to coordinate your main speakers with your subwoofer, doing so without any DSP or analog-to-digital technology at all.

SPL Crossover

The unit splits your signal, diverting midrange and high-range audio to your main monitors, and leaving the lows to route to the subs. The design utilizes SPL’s 120V rail technology to ensure high headroom and crystal clear performance, and makes use of switches and pots to select among crossover frequencies, phase positions, low-level, and more.

It’s designed to work in both 2.1 and 2.2 setups, so if you utilize stereo subwoofers, this device will be suitable for your uses.

  • Active or passive: Active
  • Inputs:
    • 2 (left & right) balanced XLR (Impedance of 20 kΩ)
    • 2 (left & right) unbalanced RCS (Impedance of 20 kΩ)
    • 1 TS 3.5 mm (control)
  • Outputs:
    • 4 balanced XLR
      • Low output left
      • Low output right
      • Mid-high output left
      • Mid-high output right
    • 4 TS 3.5mm (control)
      • Low output left
      • Low output right
      • Mid-high output left
      • Mid-high output right
  • Crossover points: 50 to 120 Hz in 6 different steps (12 dB or 24 dB/octave)
    • 50 Hz
    • 60 Hz
    • 70 Hz
    • 85 Hz
    • 100 Hz
    • 120 Hz to 300 kHz continuously variable

Harrison Labs FMOD In-Line

Harrison Labs’ FMOD line has a 50 Hz in-line LPF (link to check the price on Amazon) and a 50 Hz in-line HPF (link to check the price on Amazon). Each of these “in-line crossovers” come as a set of 2 and connect via RCA

Harrison Labs FMOD 50 Hz LPF (left) & HPF (right)

miniDSP 2×4

The miniDSP 2×4 (link to compare prices on Amazon and select retailers) in a box is a flexible pocket size DSP processor with 2 x analog IN, 4 x analog OUT.

miniDSP 2×4

Combined with a plug-in software for programming, one can configure the on board Audio processing filters real time from a PC or Mac environment.

Once the board configured, the device operates standalone and doesn’t require a computer anymore.

This 2-way or 4-way digital crossover is excellent as a subwoofer processor; as an car audio crossover, and in DIY audio projects.

  • Active or passive: Active (DSP)
  • Inputs: 2 (left & right) unbalanced RCA (Impedance of 6 kΩ)
  • Outputs: 4 unbalanced RCA (Impedance of 560 Ω)
  • Crossover points: 50 to 120 Hz in 6 different steps (12 dB or 24
  • ADC/DAC data resolution: 24-bit
  • Digital signal processor engine: 28/56 bit DSP engine with double-precision processing

What is the difference between an active and a passive speaker? The simple difference between active and passive speakers is that active speakers require power and passive speakers don’t. This is because active models have built-in amplifiers while passive models require external amplifiers.

For more information on passive and active speakers, check out my article What Are The Differences Between Passive & Active Speakers?

Can you connect a passive speaker to an active speaker? No. The amps within an active speaker are designed in the context of the active crossover network and are made to drive the individual driver(s) of the active speaker. Connecting a passive speaker to an active speaker would not work in series for this reason and would not work in parallel since it would only be receiving line level (or else the active speaker would be receiving speaker level from the passive speaker’s external amp).

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