Audio crossovers is a type of electronic filter circuit used in various audio applications, to separate audio signals into two or more frequency ranges, so that signals can be sent to drivers designed for different frequency ranges. Crossovers are often described as "two-way" or "three-way", which indicate, respectively, that the crossover divides the given signal into two frequency ranges or three frequency ranges. Crossovers are used in loudspeaker cabinets, power amplifiers in consumer electronics (hi-fi, home cinema sound and car audio) and pro audio and instrument instrument amplifier. For the last two markets, crossovers are used in bass amplifiers, keyboard amplifiers, bass and keyboard enclosures and sound amplifier systems (PA speakers, monitor speakers, subwoofer systems, etc.).
Crossover is used because most individual speaker drivers are incapable of covering the entire audio spectrum from low frequency to high frequency with acceptable relative volume and no distortion. Most hi-fi speaker systems and speaker speakers are a combination of several loudspeaker drivers, each serving a different frequency band. A simple example of a standard is a hi-fi and PA cabinet system that contains woofers for low and medium frequencies and tweeters for high frequencies. Because the source of the sound signal, whether it is recording music from a CD player or mixed live band from the audio console has all the low, medium and high combined frequencies, the crossover circuit is used to split the audio signal into a separate frequency band that can be routed separately to the loudspeaker, tweeter or horn that is optimized for that frequency band.
Active crossovers are distinguished from passive crossovers whereas passive crossovers divide reinforced signals coming from one power amplifier so that it can be sent to two or more drivers (eg, woofers and very low frequency subwoofer, or woofer and tweeter), an active crossover divides the signal audio before amplification, so it can be sent to two or more power amplifiers, each of which is connected to a separate driver type. The home cinema 5.1 surround sound audio system uses a crossover that separates low frequency signals, so it can be sent to the subwoofer, and then sends mid- and high-range frequencies to five speakers placed around the listener; in a typical application, the signals sent to the surround speaker cabinets are further divided by passive crossover into medium/low range woofers and high range tweeter. Active crossovers come in digital and analog varieties.
Active digital crossovers often include additional signal processing, such as limiting, delaying, and even distribution. Crossover signals allow audio signals to be divided into bands that are processed separately before they mingle again. Some examples are multiband dynamics (compression, limiting, de-essing), multiband distortion, increased bass, high frequency exciters, and noise reduction such as Dolby A noise reduction.
Video Audio crossover
Overview
The definition of an ideal audio crossover change relative to the task and audio application at hand. If the separated bands are re-mixed together (as in multiband processing), the ideal audio crosses breaks the audio signals into non-overlapping or interacting bands that produce output signals unchanged in frequency, relative level, and phase response. This ideal appearance can only be estimated. How to apply the best approach is a matter of lively debate. On the other hand, if the audio crossover separates the audio bands in the loudspeaker, there is no requirement for the ideal mathematical characteristics in the crossover itself, since the frequency and response phases of the loudspeaker drivers in their buffering will surpass the results. The satisfactory output of a complete system consisting of audio crossover and the loudspeaker driver in their enclosure (s) is the design goal. Such targets are often achieved by using non-ideal and asymmetrical crossover filter characteristics.
Many different types of crossovers are used in audio, but generally include one of the following classes.
Maps Audio crossover
Classification
Classification by the number of filter sections
Speakers are often grouped as "N-way", where N is the number of drivers in the system. For example, the speaker with the woofer and tweeter is 2 directions. N-way speakers usually have a N-way crossover to split signals between drivers. The 2-way crossover consists of low-pass and high-pass filters. A 3-way crossover is built as a combination of low-pass, band-pass and high-pass filter (LPF, BPF and HPF respectively). The BPF section in turn is a combination of the HPF and LPF parts. 4 (or more) crossovers are not very common in speaker design, especially because of the complexity involved, which is generally not justified by better acoustic performance.
Additional HPF sections may be present in the "N-way" loudspeaker crossover to protect the lowest frequency drivers from lower frequencies than can be handled safely. Such a crossover would then have a bandpass filter for the lowest frequency driver. Similarly, the rider with the highest frequency may have a protective LPF part to prevent high frequency damage, although this is much less common.
Recently, a number of manufacturers started using the "N.5-way" crossover technique for crossover loudspeaker stereo. It usually shows the addition of a second woofer that plays the same bass range as the main woofer but rolls long before the main woofer.
Description: The filter sections mentioned here are not to be confused with individual 2-pole filter parts that have higher order filters.
Classification by component
Crossovers can also be classified by type of component used.
Passive
A passive crossover divides the audio signal after being amplified by a single power amplifier, so the amplified signal can be sent to two or more driver types, each representing different frequency ranges. The crossover is made entirely of passive components and circuits; the term "passive" means that no additional resources are required for the circuit. A passive crossover only needs to be connected with a cable to a power amplifier signal. Passive crossovers are usually set in Cauer topology to achieve the Butterworth filter effect. Passive filters use resistors in combination with reactive components such as capacitors and inductors. Highly passive passive crossover tends to be more expensive than active crossovers because individual components are capable of producing good performance at high currents and voltages where loudspeaker systems are difficult to manufacture.
Inexpensive consumer electronics products, such as low-cost home theater in box packages and inexpensive boom boxes use low-quality passive crossovers. The expensive hi-fi speaker and receiver systems use higher quality passive crossovers, to get better sound quality and lower distortion. The same price/quality approach is used with sound reinforcement system equipment and amplifiers of musical instruments and speaker cabinets; low cost stage monitors, PA speakers, or amplifier amplifier speakers will typically use lower quality, passive crossovers at lower prices, while high priced and high quality cabinets will use better quality crossovers. Passive crossovers can use capacitors made of polypropylene, metalized polyester foil, paper and electrolytic capacitor technology. The inductor may have an air core, a powdered metal core, a ferrite core, or a laminated silicon steel core, and most of the wound with enamelled copper wire.
Some passive networks include devices such as fuses, PTC devices, lights or circuit breakers to protect the loudspeaker drivers from unintentional forces (for example, from spikes or sudden spikes). Modern passive crossover increasingly combines equalization networks (eg, Zobel networks) that compensate for impedance changes with frequencies attached to almost any loudspeaker. The problem is complex, because part of the impedance change is due to the acoustic loading changes in the passband of the driver.
On the negative side, passive networks may be large and cause loss of power. They are not only specific frequencies, but also specific impedances. This prevents interchangeability with the speaker system from different impedances. The ideal crossover filters, including impedance compensation and an equalization network, can be very difficult to design, because the components interact in a complex way. The crossover design expert Siegfried Linkwitz said among them that "the only reason for passive crossover is low cost." Their behavior changes with the dynamics depending on the driver signal level, they block the power amplifier from taking maximum control over the voice coil movements they are a waste time, if the accuracy of reproduction is the goal. "Alternatively, passive components can be used to build filter circuits before amplifiers. This is called passive strip crossover.
Active
Active crossover contains active components in the filter. In recent years, the most commonly used active device is the op-amp; Active crossovers are operated at a level suitable for different power amplifier inputs with passive crossovers that operate after power amplifier output, at high currents and in some cases high voltages. On the other hand, all circuits with gain introduce noise, and the noise has a damaging effect when introduced before the signal is amplified by the power amplifier.
Active crossover always requires the use of power amplifier for each output band. So an active 2-way crossover requires two amplifiers - one each for woofers and tweeters. This means that an active crossover-based system will often cost more than passive crossover based systems. Despite the cost and complexity losses, active crossovers provide the following advantages over the passive:
- independent frequency response from dynamic changes in driver electrical characteristics.
- Usually, it's probably an easy way to change or customize each frequency band to the specific driver used. Examples are cross slope, filter type (eg, Bessel, Butterworth, etc.), Relative rate,...
- better isolation of any driver from signals handled by other drivers, thereby reducing intermodulation and overdriving distortion
- The power amplifier is directly connected to the speaker driver, thus maximizing the speaker loudspeaker control from the speaker sound coil, reducing the consequences of the dynamic changes in the driver's electrical characteristics, all of which tend to increase the transient response of the system
- reduction of power amplifier output requirement. Without energy lost in passive components, the amplifier requirements are reduced considerably (up to 1/2 in some cases), reducing costs, and potentially improving quality.
Digital
Active crossovers can be implemented digitally using DSP chips or other microprocessors. They use a digital approach to traditional analog circuits, known as IIR filters (Bessel, Butterworth, Linkwitz-Riley, etc.), or they use Finite Impulse Response filters (FIRs). The IIR filter has much in common with analog filters and relatively lightweight CPU resources; FIR filters on the other hand usually have a higher order and hence require more resources for similar characteristics. They can be designed and built so that they have a linear phase response, which is considered to be desired by many people involved in sound reproduction. However there is a disadvantage - to achieve a linear phase response, longer delay time occurs than is required with a IIR or minimum phase FIR filter. The IIR filters, which are naturally recursive have the disadvantage that if not carefully designed, they can enter the boundary cycle that results in non-linear distortion.
Mechanical
This crossover type is mechanical and uses the properties of the materials inside the driver's diaphragm to achieve the necessary filtering. Such crossovers are commonly found in full-range speakers designed to cover as many audio tapes as possible. One of them is built by coupling the cone from the speaker to the coil of the sound coil through the corresponding portion and directly installing the small cone whizzer to the coil. This corresponding section serves as a compliant filter, so the main cone is not vibrated at a higher frequency. The whizzer cone responds to all frequencies, but because of its smaller size it only provides useful output at higher frequencies, thus applying mechanical crossover functions. Careful selection of materials used for cone, whizzer and suspension elements determine crossover frequency and crossover effectiveness. Such mechanical displacements are complicated to be designed, especially if high fidelity is desired. Computer-aided design largely replaces the grueling trial and error approach that historically used. For several years, material compliance may change, negatively affecting the frequency response of the speaker.
A more general approach is to use a dust cap as a high-frequency radiator. The dust cover emits low frequencies, moves as part of the main assembly, but due to the low mass and reduced attenuation, radiates increased energy at higher frequencies. Like the whizzer cone, careful selection of materials, shapes, and positions is required to produce smooth and extended output. High frequency dispersion is somewhat different for this approach than for whizzer cone. The related approach is to form the main cone with the profile, and the materials, that the neck area remains more rigid, emit all the frequencies, while the outer area of ​​the cone is selectively separated, radiating only at lower frequencies. Profiles and cone materials can be modeled in FEA software and predictable results for excellent tolerance.
Speakers that use this mechanical crossover have several advantages in sound quality despite the difficulty of designing and making them, and regardless of the inevitable limitations of output. Full-range drivers have single acoustic centers, and can have relatively simple phase shifts across the audio spectrum. For best performance at low frequencies, these drivers require careful enclosure design. Its small size (usually 165 to 200 mm) requires considerable conic voyage to produce effective bass sounds, but the short voice coils required for reasonable high-frequency performance can only travel within a limited range. However, within these limits, costs and complications are reduced, as crossovers are not required.
Classification based on the order or slope of the filter
Just as filters have different orders, so does crossovers, depending on the slope of the filter they apply. The final acoustic slope may be completely determined by the electrical filter or can be achieved by combining the slope of the electrical filter with the driver's natural characteristics. In the previous case, the only requirement is that each driver has a flat response at least to the point where the signal is about -10dB down from the passband. In the latter case, the final acoustic slope is usually steeper than the electrical filter used. A third or fourth acoustic crossover often has only a second-order electrical filter. This requires that the speaker driver behave well in a sufficient way from the nominal crossover frequency, and further that the high frequency driver can survive considerable input in the frequency range below the crossover point. This is difficult in actual practice. In the discussion below, the electrical filter order characteristics are discussed, followed by a discussion of acoustically sloped crossovers and their advantages or disadvantages.
Most audio crossovers use first-order electrical filters to the fourth. Higher orders are generally not implemented in passive crossovers for loudspeakers, but are sometimes found in electronic equipment in circumstances where the cost and great complexity can be justified.
First order
The first-order filter has a slope of 20 dB/decade (or 6 dB/octave). All first-order filters have the characteristics of the Butterworth filter. First-order filters are considered by many audiophiles to be ideal for crossovers. This is because this type of filter is 'whilst perfect', which means it passes both amplitude and phase unchanged across the entire interest range. It also uses the least part and has the lowest insertion loss (if passive). A first order crossover allows more unwanted frequency signals to pass through the LPF and HPF sections rather than higher order configurations. While woofers can easily take this (in addition to generating distortion at the above frequencies they can handle correctly), the smaller high frequency drivers (especially tweeters) are more likely to be damaged because they are not able to handle large power inputs at frequencies below their value crossover point.
In practice, loudspeaker systems with true first-order acoustic slogans are difficult to design because they require a large overlapping bandwidth of drivers, and shallow slopes mean that non-coincident drivers interfere with a wide frequency range and cause a large response to shift from the axis.
Second order
The second order filter has a 40 dB/decade (or 12 dB/octave) slope. Second-order filters can have Bessel, Linkwitz-Riley or Butterworth characteristics depending on the design options and the components used. This sequence is typically used in passive crossovers because it offers a reasonable balance between complexity, response, and protection of higher frequency drivers. When designed with parallel physical placement time, this crossover has a symmetrical pole response, as do all even order crossovers.
It is generally thought that there will always be a 180 Â ° phase difference between the output of the low-pass filter (second order) and the high-pass filter having the same crossover frequency. Thus, in 2-way systems, high-pass section output is usually connected to an inverted high-frequency driver, to correct this phase problem. For a passive system, the tweeter is connected with the opposite polarity to the woofer; for active crossover reversed high-pass filter output. In a 3-way system the driver or mid-range filter is reversed. However, this is generally only true when the speakers have extensive overlap responses and the acoustic centers are physically aligned.
Third order
The third order filter has a slope of 60 dB/decade (or 18 dB/octave). This crossover usually has the characteristics of the Butterworth filter; the phase response is very good, the number of levels are flat and in quadrature phase, similar to the first order crossover. The polar response is asymmetrical. In the original array of MTM D'Appolito, symmetric driver settings are used to generate symmetric off-axis responses when using a third-order crossover. Third-order acoustic crossovers are often built from first or second order filter circuits.
Fourth order
The fourth order filter has a slope of 80 dB/decade (or 24 dB/octave). These filters are complicated to be designed in passive form, because the components interact with each other. Steep-slope passive networks are less tolerant of value deviations or tolerance values, and are more sensitive to mis-termination with reactive driver loads. A 4th crossover with a crossover point of -6 dB and a flat sum is also known as the Linkwitz-Riley crossover (named after its discoverer), and can be constructed in active form by deriving two parts of the second-order Butterworth filter. The output signal from this crossover command is in phase, thus avoiding partial phase inversion if the bandpass crossover is summed electrically, as it will be in the output stage of the multiband compressor. The crossover used in the loudspeaker design does not require parts of the filter to be in phase: smooth output characteristics are often achieved using non-ideal, asymmetric crossover filter characteristics. Bessel, Butterworth and Chebyshev are among the possible crossover topologies.
Such steep-slope filters have bigger problems with overshoot and ringing but there are some key advantages, even in their passive forms, such as the potential of lower crossover points and improved power handling for tweeter, along with less overlap between drivers, dramatically reduce catapult, or other unwanted off-axis effects. With less overlap between adjacent drivers, their location relative to each other becomes less important and allows more latitude in the cosmetic speaker system or (in car audio) practical installation constraints.
Order higher
Passive crossovers that provide higher acoustic slopes than the fourth order are not common due to cost and complexity. Filters up to 96 dB per octave are available in active crossover and loudspeaker management systems.
Mix order
Crossovers can also be built with mixed filters. For example, a second order low order is combined with a third high-order path. These are generally passive and are used for several reasons, often when component values ​​are discovered by computer program optimization. Crossover tweeter with a higher order can sometimes help compensate for the offset time between the woofer and the tweeter, caused by an incorrect acoustic center
Classification by circuit topology
Parallel
Parallel crossover is the most common. Electrically the filters are parallel and thus the various parts of the filter do not interact. This makes the two-way crossover easier to design because, in the case of electrical impedance, parts can be considered apart and because the tolerance variation of the components will be isolated but like all crossovers, the final design relies on the output of the driver to complement acoustically. and this in turn requires a careful match in the amplitude and phase of the underlying crossover. Parallel crossover also has the advantage of enabling speaker drivers to be bi-wired whose benefits are heavily debated.
Series
In this topology, individual filters are connected in series, and driver or driver combinations are connected in parallel with each filter. To understand the signal paths in this crossover type, see the "Crossover Series" image, and consider the high frequency signal which, during a given moment, has a positive voltage on the upper Input terminal as opposed to the lower Input terminal. The low pass filter (LPF) presents a high impedance to the signal, and the tweeter presents a low impedance; so signal passes tweeter. The signal continues to the connection point between the woofer and the high pass filter (HPF). There, the HPF presents a low impedance to the signal, so the signal passes through the HPF, and appears in the lower Input terminal. The low frequency signal with the same instantaneous voltage characteristics first passes through the LPF, then the woofer, and appears in the lower Input terminal.
Derived
The derived crossover includes an active crossover in which one crossover response comes from another through the use of a differential amplifier. For example, the difference between the input and output signals of the high pass section is the low pass response. Thus, when a differential amplifier is used to extract this difference, its output forms a low pass filter. The main advantage of derived filters is that they do not produce phase differences between high pass and low passages at any frequency. The disadvantages, too
- (a) that high pass and low pass section often have different attenuation levels in their stop band ie , their slopes are asymmetric, or
- (b) that the response of one or both sections peaks near the crossover frequency,
or both. In the case of (a), above, the usual situation is that the lowered feedback response is lowered to a much slower rate than the fixed response. This requires a speaker who is directed to continue to respond to a distant signal into a stopband where his physical characteristics may not be ideal. In the case of (b), above, both speakers are required to operate at a higher volume level as the signal approaches the crossover point. It uses more reinforcement power and can push the speaker cone into non-linearity.
Model and Simulation
Professionals and fans have access to a variety of computer tools that were not previously available. This computer-based measuring and simulation tool enables virtual modeling and design of various parts of the speaker system that greatly accelerate and improve speaker quality. These tools range from commercial offerings to free. Their scope also varies. Some may focus on woofer/cabinet design and problems associated with volume and port (if any) while others may focus on crossover and frequency response. Some tools for example only simulate baffle step responses.
In the period before computer modeling made it affordable and quick to simulate the combined effect of drivers, crossovers and cabinets a number of problems could be missed by the attention of the speaker designer. For example, a simple three-way crossover is designed as a pair of two-way crossover: tweeter/midrange and the other midrange/woofer. This can result in gain gain and 'haystack' response in the midrange output, along with lower than anticipated input impedance. Other problems such as improper phase matching or incomplete modeling of the driver impedance curve may also escape attention. These problems are not impossible to solve, but require more iterations, time and effort than they do today.
See also
- Bass Management
- Electrical characteristics of dynamic loudspeaker
- Supported speakers
- loudspeaker casing
- Speaker complete
- Tweeter
- Super tweeter
- Midrange loudspeakers
- Woofer
- Subwoofer
References
External links
- Lenard Education on a crossover describes an audio crossover overview.
- diyAudioAndVideo.com - DIY Audio site with information on building crossovers. Includes a crossover calculator for 15 different crossover types.
- KS Digital - maker of multiple loudspeakers with digital crossover
- Articles on active crossovers
- Comparison of active and passive crossovers
- Parallel series and parallel comparison
- Description of the L-R crossover
- Passive crossover design article
- Linkwitz Lab Crossovers
- Linkwitz-Riley Crossovers: A Primer
- FIR Crossover Digital Linear Phase System Design
- Full Driver & amp; Loudspeaker Theory
- Filter & amp; Audioholics.com; Crossover Type
- Bessel Crossover Filters, and Their Relationships with Others
- Active Lowpass Filter Design
Source of the article : Wikipedia
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