An often asked question is,” What are Speaker Crossovers and what do they do? To those without experience, the concept can sound quite daunting. We will answer the question and help you to understand the basics. We will try not to get too complex.
Why speaker crossovers are needed
Individual loudspeaker drivers are not able to cover the entire audio spectrum from low to high frequencies with an acceptable volume and the absence of distortion. The speaker crossover is a component found in almost all Loudspeaker cabinets, Power amplifiers, Home Cinema 5.1 surround sound audio systems, and car audio systems.
A crossover is an electronic circuitry filter that blocks out unfiltered frequencies to the driver within a speaker or group of speakers. The general rule is that every speaker that has more than one driver requires a crossover.
The crossover network splits an audio signal and directs different frequencies to the right loudspeaker drivers designed to operate within different frequency ranges. This allows a group of specific frequencies to be sent to the driver in each speaker allowing that speaker to play efficiently and effectively.
How speaker crossover works in practice
If you look, for example, at high frequencies, the crossovers will control frequencies to confirm that only tweeters get the very high frequencies and none of the low frequencies that the driver was not designed to deliver.
This results in the system’s volume potential and clarity being vastly improved, as each driver in a speaker is responsible only for those frequencies that it will reproduce most effectively.
Frequencies have been mentioned often in this introduction. Sound waves are movements of air molecules that our ears translate into sound and frequency refers to the number of cycles (oscillations) these waves produce in a second. Measured as hertz or Hz.
Therefore, a 20Hz tone will vibrate 20 times per second.
A lower frequency is a lower pitch and a higher frequency will be a higher pitch. An audio filter is a circuit that allows a specific range of frequencies to be sent to the driver.
There are three types of filters:
- A High-pass filter (HPF) – This Filter allows frequencies above the chosen cut-off frequency to pass through to a speaker and also limits frequencies that are too low for that driver to operate efficiently
- A Low-pass filter (LPF) – This Filter allows all frequencies below the chosen cut-off frequency to pass through to a speaker. A ceiling is set to cut out any high frequencies.
- A Band-pass filter (BPF) – This filter uses a combination of a High Pass Crossover and a Low Pass Crossover to allow a range of frequencies higher or lower than 2 decided frequencies (one High Pass and one Low Pass) to pass through to a driver.
Human ears can register sounds from about 20 Hz up to 20000 Hz.
The frequencies can be divided into:
- High frequency – Tweeter (small diaphragm ) 2000 Hz – 20000 Hz
- Mid-range frequency – ( slightly larger diaphragm) 250 – 4000 Hz
- Low range frequency – Woofer ( larger diaphragm ) 50 – 1000 Hz
- Low range frequency – Subwoofer (very large diaphragm) 20 – 200 Hz
A speaker crossover will ensure that tweeters only receive the highest frequency signals, nothing lower.
Crossovers help to avoid resonant frequencies. This refers to the frequency at which the cabinet surrounding one or more drivers is made to vibrate.
2-Way, 3-Way, and 4-Way Crossovers
A 2-way speaker crossover will divide the frequency range between two speakers. Speaker systems provide these crossover networks with two drivers. A tweeter and a woofer.
High audio frequencies are transferred to the tweeter through HPF and the low frequencies are sent to the woofer through LPF.
A 3-way crossover will include three filters. HPF, BPF, and LPF.
3-way systems use this system to divide the frequencies into low, middle, and high-range frequencies. Mid-range frequencies are sent in the direction of the mid-range speakers.
A 4-way crossover system, by contrast, will send signals to, you guessed it, 4 drivers. These drivers are normally a woofer, a mid-range speaker, a tweeter, and a super tweeter.
The sound frequency is reproduced as lows, mids/low-mids, highs/high-mids, and highs/ super-highs. If the system has a super tweeter, the extra filter will only allow ultra-high frequencies to pass through.
The Home cinema 5.1 surround sound audio systems use a crossover that separates the very-low-frequency signal so that it can be sent to a subwoofer.
The remaining low, mid-and high -range frequencies are sent to the other 5 speakers which are placed around the room.
The signals to these speakers are further split up using a passive crossover into a low/mid-range woofer and a high-range tweeter.
Active vs. Passive Crossovers
The crossover filters can be “active” or “passive” and are described as two-way or three-way, meaning that the crossover splits a signal into two or three frequency ranges respectively.
Passive crossovers use a network of passive electrical components such as ( capacitors, inductors and, resistors ) to split up an amplified signal.
This enables the amplified signal to be sent to two or more drivers, such as (a woofer and a tweeter) or ( a sub-woofer, a woofer, and a tweeter)
Active Crossovers use a Microprocessor to split and transmit frequencies to the specified server.
Here are the differences as well as the pros and cons of passive vs. active crossover:
|Between amp and speaker
|Between receiver and amp
|Splitting an amplified signal and delivering to multiple drivers
|Using low signals and splitting the frequencies by use of line-level signals
|Medium with less accuracy
Both high and low-pass filters can filter signals of different strengths. These are referred to as orders. Usually, only filters between the first and fourth-order are used.
Filters can be classified based on their octave slope which is measured in dB (decibels).
A first-order filter can block signals up to 6 dB and a fourth-order filter can block filters up to 24 dB per octave.
Crossovers are essential. It is like the brain of a loudspeaker. It controls the range of frequencies that each driver is optimized to reproduce.
A loudspeaker system that does not have a properly designed crossover can cause an excess in frequency overlap between drivers which can increase distortion and lead to poor sound quality and eventually damage the driver.