Audio crossovers are a class of electronic filters designed specifically for use in audio applications, especially hi-fi. Commonly used loudspeaker drivers are incapable of covering the entire audio spectrum with acceptable loudness and lack of distortion by themselves. Thus, crossovers serve the purpose of splitting the audio signal into separate frequency bands which can be handled by individual loudspeaker drivers optimized for those bands. A combination of multiple drivers each catering to a different frequency band is the design pattern for most hi-fi speaker systems. An audio crossover may also be constructed mechanically and is commonly found in full-range speakers, portions of whose cones/dust caps/whizzer cones are decoupled at progressively higher frequencies. Television signal splitter consisting of a hi-pass and a low-pass filter. ... High Fidelity is also the title of a book by Nick Hornby and a film directed by Stephen Frears, based upon Hornbys book. ... This article or section needs copy editing for grammar, style, cohesion, tone and/or spelling. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... This article or section needs copy editing for grammar, style, cohesion, tone and/or spelling. ... High Fidelity is also the title of a book by Nick Hornby and a film directed by Stephen Frears, based upon Hornbys book. ... Cross-section of a full-range loudspeaker. ...

Another use of crossovers is multiband processing, in which the audio signal is split into bands, which are adjusted (equalized, compressed, echoed, etc) separately. After the adjustments, the individual bands are mixed together again. Some examples are: multiband dynamics (compression, limiting, de-essing), multiband distortion, bass enhancement, high frequency exciters, noise reduction (for example: Dolby A noise reduction). For information about computer bandwidth management, see Equalization (computing). ... This article is about audio effect. ... Audio level compression, also called dynamic range compression, volume compression, compression, limiting, or DRC (often seen in DVD player settings) is a process that manipulates the dynamic range of an audio signal. ... Audio level compression, also called dynamic range compression, volume compression, compression, limiting, or DRC (often seen in DVD player settings) is a process that manipulates the dynamic range of an audio signal. ... In audio processing, De-essing is bandwidth-limited compression intended to reduce or eliminate excess sibilance in sound recordings of the human voice. ... A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. ... Noise reduction is the process of removing noise from a signal. ... Dolby NR is a noise reduction system developed by Dolby Laboratories for use in analogue magnetic tape recording. ...

Overview

Comparison of the magnitude response of 2 pole Butterworth and Linkwitz-Riley crossover filters. The summed output of the Butterworth filters has a +3dB peak at the crossover frequency.

An ideal audio crossover would split the incoming audio signal into separate bands that do not overlap or interact and which, when added together, output the signal unchanged in both frequency, relative levels, and phase response. This behavior cannot be achieved in practice, but can be approximated. Just which is the best approximation is a matter of lively debate. Many different crossover types are used, but they generally fall under one of the classifications provided below. Image File history File links Linkwitz_vs_Butterworth. ... Image File history File links Linkwitz_vs_Butterworth. ... Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ... Phase response is the relationship between the phase of a periodic input and an ouput signal passing through any device which accepts an input and produces an output signal such as an amplifier or a filter. ...

Crossover classification

Classification based on the number of filter sections

In loudspeaker specifications, one often sees a speaker classified as an "N-way" speaker. N is a positive whole number greater than 1, and it indicates the number of filter sections. A 2-way crossover consists of a low-pass and a high-pass filter. A 3-way crossover is constructed as a combination of low-pass, band-pass and high-pass filters (LPF, BPF and HPF respectively). The BPF section is in turn a combination of HPF and LPF sections. 4 (or more) way crossovers are not very common in speaker design, primarily due to the complexity involved, which is not generally justified by better acoustic performance. A low-pass filter passes low frequencies fairly well, but attenuates, or blocks, high frequencies. ... In J. R. R. Tolkiens fiction of Middle-earth, the High Pass is a pass over the Misty Mountains. ... A low-pass filter passes low frequencies fairly well, but attenuates, or blocks, high frequencies. ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... In J. R. R. Tolkiens fiction of Middle-earth, the High Pass is a pass over the Misty Mountains. ...

Recently, a number of manufacturers have developed what is often called "N.5-way" crossover techniques. This usually indicates the addition of an extra bass driver (commonly termed a subwoofer when limited to only low frequencies below all other drivers) with a crossover designed such that it augments the bass response or compensates for cabinet diffraction effects. a 12 subwoofer driver A subwoofer is a type of driver dedicated to the reproduction of bass frequencies, typically from about 20 Hz to perhaps 200 Hz in cone speakers, and in the case of a rotary woofer, all the way down to below 1 Hz. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ...

Remark: Filter sections mentioned here is not to be confused with the individual 2-pole filter sections that a higher order filter consists of.

Classification based on components

Crossovers can also be classified based on the design approach (ie, more or less, the type of components used).

Passive crossovers

A passive crossover is made entirely of passive components, arranged most commonly in a Cauer topology to achieve a Butterworth filter. Passive filters use both non reactive resistors, and reactive components such as capacitors and inductors. Very high performance passive crossovers may be more expensive than active crossovers. The use of non inductive resistors and special capacitor components adds significant cost, although they have some sonic benefits. Polypropylene and Metalizied polyester foil, and paper-electrolytic capacitors are common. Inductors may have air cores, powdered metal cores, ferrite cores, or laminated silicon steel cores, and most are wound with insulated copper 'magnet wire'. Some passive networks include devices such as fuses, PTC devices, bulbs or circuit breakers, to protect the loudspeaker drivers from accidental overpowering. On the negative side, The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Butterworth may refer to people with the surname: Bob Butterworth, former Florida attorney general George Butterworth, a composer Mary Butterworth, a colonial counterfeiter S. Butterworth, the inventor of the Butterworth filter Butterworth may also be referred to these following places: Butterworth, Penang, a town located in Province Wellesley, Penang, Malaysia... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap Micrograph of polypropylene Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including food packaging, ropes, textiles, plastic parts... SEM picture of a bend in a high surface area polyester fiber with a seven-lobed cross section Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. ... An electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. ... Ferrite may refer to: Ferrite (magnet)s (e. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Standard atomic weight 63. ... The word fuse (spelled fuze in some contexts) has several meanings: To fuse is to combine in a process of fusion. ... A circuit breaker is a piece of equipment which is designed to protect an electrical apparatus from damage caused by overload or short circuit. ...

• Passive networks may be bulky and cause some power loss.
• Networks are not only frequency specific, but also impedance specific. Passive crossovers are not generally interchangable between different speaker systems.
• Correct crossover filters, including impedance compensation and equalization neworks can be very difficult to design, as the componets interact in complex ways. This is an area where computer simulation is almost mandatory.

In electrical engineering, Impedance is a measure of opposition to a sinusoidal electric current. ...

Active crossovers

An active crossover contains active components (ie, those with gain) in its filters. In recent years, the most commonly used active device is an op-amp; active crossovers are operated at levels suited to power amplifier inputs in contrast to passive crossovers which operate after the power amplifier's output, at high voltage and current levels. On the other hand, all circuits with gain introduce noise, and in this case, unless carefully designed, the noise will be amplified by the power amplifiers, perhaps unacceptably. An operational amplifier or op-amp is an electronic circuit module (normally built as an integrated circuit, but occasionally with discrete transistors or vacuum tubes) which has a non-inverting input (+), an inverting input (-) and one output. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Look up current in Wiktionary, the free dictionary. ... In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... For the Irish mythological figure, see Naoise. ...

Active crossovers always require the use of power amplifiers for each output band. Thus a 2-way active crossover needs two amplifiers — one each for the woofer and tweeter. This means that an active crossover based system will often cost more than a passive crossover based system, although none of the amplifiers needs to provide output as high as for an equivalent sound level full-frequency, power amplifier, which reduces cost. Generally, active crossovers require use of tweeter protection (typically a small capacitor) since the tweeter is now directly connected to an amplifier and may be damaged due to DC in that output, or a short thump produced when an amplifier turns on or off. The cost and complication disadvantages of active crossovers are offset by the following gains:

• a frequency response independent of the dynamic changes in a driver's electrical characteristics.
• typically, the possibility of an easy way to vary or fine tune each frequency band to the specific drivers used. Examples would be crossover slope, filter type (eg, Bessel, Butterworth, etc), relative levels, ...
• isolation of each driver from signals handled by drivers, thus reducing intermodulation distortion and overdriving
• The power amplifiers are directly connected to the speaker drivers, thereby maximizing amplifier damping control of the speaker voice coil, reducing consequences of dynamic changes in driver electrical characteristics, all of which are likely to improve the transient response of the system
• reduction in power amplifier cost and output requirement. With no energy being lost in passive components, amplifier requirements are reduced considerably (up to 1/2 in some cases), reducing costs, and potentially increasing quality.

In electronics and signal processing, a Bessel filter is a variety of linear filter with a maximally flat group delay (linear phase response). ... The Butterworth filter is one type of electronic filter design. ... It has been suggested that intermodulation distortion be merged into this article or section. ...

Mechanical crossovers

Main article: Full-range

This crossover type is mechanical and uses the properties of the materials in a driver diaphragm to achieve the necessary filtering. Such crossovers are commonly found in full-range speakers which are designed to cover as much of the audio band as possible. One such is constructed by coupling the diaphragm of the speaker to the voice coil through a compliant section and directly attaching a small light-weight cone called whizzer to the voice coil. The compliant section is intended to ensure that the primary diaphragm responds only to lower frequencies while the whizzer, which is directly coupled to the voice coil, responds only to the rapid movements of the coil at higher frequencies. This combination results in the main diaphragm having an upper cut-off frequency while the characteristics of the whizzer and voice coil set the lower limit to the whizzer's response, thereby implementing a crossover action. The choice/weight of materials used for the diaphragm, whizzer and the speaker's suspension determine the crossover frequency and the effectiveness of the crossover. This sort of crossover is much more complex to design, especially if the highest degree of performance is desired. Extensive trial and error is required. Over several years, the compliance of the joint can change, negatively effecting the response of the speaker. Cross-section of a full-range loudspeaker. ... Cross-section of a full-range loudspeaker. ...

An alternative is to use the dust cap as a high frequency radiating device, also crossed over by mechanical compliance from the primary diaphragm. High frequency dispersion is somewhat different for this approach than for whizzer cones. Another possibility is to build the primary cone with such profile, and of such materials, that the neck area remains rigid, radiating all frquencies, while the outer areas of the cone are selectively decoupled, radiating only at lower freqencies. Look up diaphragm in Wiktionary, the free dictionary. ... Dispersion can mean any of several things: A phenomenon that causes the separation of a wave into components of varying frequency. ...

Speakers which use these mechanical crossovers have some advantages in sound quality despite the difficulties of designing and manufacturing them, and despite the inevitable output limitations. Full-range drivers have a single acoustic center, and can have relatively modest phase change across the audio spectrum. For best performance at low frequencies, these drivers require careful enclosure design. Their small size (typically 165 to 200mm) requires considerable cone excursion to reproduce bass, but have short voice coils, demanded for reasonable high frequency performance, incapable of the large cone motions required for bass. But wihtin these constraints, cost and complications are reduced, as no crossovers are required.

Those who do not prefer the sound of fullrange drivers (eg, a lack of powerful bass and usually strong highs) sometimes argue that a single diaphragm that must produce both low and high frequencies does neither justice. See full-range speaker for construction details. Cross-section of a full-range loudspeaker. ...

Digital Crossovers

Active crossovers can be implemented digitally using a DSP chip or a microprocessor. They either use the digital approximations of traditional analog IIR filters (Bessel, Butterworth, Linkwitz-Riley etc.), having similar character to the analog versions, or they use Finite impulse response (FIR) filters. FIR filters can be constructed easily using DSP chips or microprocessors. They usually have a higher order, but their behaviour is different. They can be designed and built so that they have a linear phase response, which is desirable in sound reproduction. As a result, they are often used as crossovers in digital signal processing. Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... Analog electronics are those electronic systems with a continuously variable signal. ... IIR (infinite impulse response) is a property of signal processing systems. ... In electronics and signal processing, a Bessel filter is a variety of linear filter with a maximally flat group delay (linear phase response). ... The Butterworth filter is one type of electronic filter design. ... Magnitude plot of 2nd and 4th order Linkwitz-Riley filters A Linkwitz-Riley (L-R) filter is an infinite impulse response filter used in Linkwitz-Riley audio crossovers, named after its inventors Siegfried Linkwitz and Russ Riley, which was originally described in Passive Crossover Networks for Noncoincident Drivers in JAES... A finite impulse response (FIR) filter is a type of a digital filter, that is normally implemented through digital electronic computation. ... Microprocessors, including an Intel 80486DX2 and an Intel 80386 A microprocessor (abbreviated as µP or uP) is an electronic computer central processing unit (CPU) made from miniaturized transistors and other circuit elements on a single semiconductor integrated circuit (IC) (aka microchip or just chip). ... Linear phase is a property of a filter, where the phase response of the filter is a linear function of frequency, excluding the possibility of wraps at . ...

Classification based on filter order or slope

Just as filters have different orders, so do crossovers, depending on the filter slope they implement. The final acoustic slope may be completely determined by the electrical filter or may be achieved by combining the electrical filter's slope with the natural characteristics of the driver. In the former case, the only requirement is that each driver has a flat response at least to the point where its signal is approximately -10dB down from the passband. In the latter case, the final acoustic slope is usually steeper than of the electrical filters used. A third or fourth order acoustic crossover often has just a 2^nd order electrical filter. This requires that speaker drivers be well behaved a considerable way from the nominal crossover frequency, and further that the high frequency driver be able to survive a considerable input in a frequency range below its crossover point. This is difficult in actual practice. In the discussion below, the characteristics of the electrical filter order is discussed, followed by a discussion of crossovers having that acoustic slope and their advantages or disadvantages.

Most audio crossovers use first to fourth order electrical filters. Higher orders are not generally implemented in passive crossovers for loudspeakers, but are sometimes found in electronic equipment under circumstances for which their considerable cost and complexity can be justified.

First order crossovers

1^st order filters have a 20 dB/decade (or 6 dB/octave) slope. All 1^st order filters have a Butterworth filter characteristic. 1^st order filters are considered by many audiophiles to be ideal for crossovers. This is because this filter type is 'transient perfect', meaning it passes both amplitude and phase unchanged across the range of interest. It also uses the fewest parts and has the lowest insertion loss (if passive). A 1^st order crossover allows signal at unwanted frequencies to get through in the LPF and HPF sections than other configurations. While woofers can easily take this (aside from generating distortion at frequencies above those they can properly handle), smaller high frequency drivers (especially tweeters) are more likely to be damaged since they are not capable of handling large power inputs at lower frequencies than their crossovers. A decade on a graphical logarithmic scale represents multiplication by 10 from the previous value. ... In music, an octave (sometimes abbreviated 8ve or P8) is the interval between one musical note and another with half or double its frequency. ... The Butterworth filter is one type of electronic filter design. ... An audiophile, from Latin audire[1] to hear and Greek philos[2] loving, can be generally defined as a person dedicated to achieving high fidelity in the recording and playback of music . ...

In practice, speaker systems with true first order acoustic slopes are difficult to design because they require large overlapping driver bandwidth, and the shallow slopes mean that non-coincident drivers interfere over a wide frequency range and cause large response shifts off-axis.

Second order crossovers

2^nd order filters have a 40 dB/decade (or 12 dB/octave) slope. 2^nd order filters can have a Bessel, Linkwitz-Riley or Butterworth characteristic depending on design choices and the components used. This order is commonly used in passive crossovers as it offers a reasonable balance between complexity, response, and higher frequency driver protection. When designed with time aligned physical placement, these crossovers have a symmetrical polar response, as do all even order crossovers. In electronics and signal processing, a Bessel filter is a variety of linear filter with a maximally flat group delay (linear phase response). ... Magnitude plot of 2nd and 4th order Linkwitz-Riley filters A Linkwitz-Riley (L-R) filter is an infinite impulse response filter used in Linkwitz-Riley audio crossovers, named after its inventors Siegfried Linkwitz and Russ Riley, which was originally described in Passive Crossover Networks for Noncoincident Drivers in JAES... The Butterworth filter is one type of electronic filter design. ... Polar may refer to: Polsk Ost med KATING WAPOOOOW CHING CHING WOWOWOWOW/Gling, Oink oink. ...

It is commonly thought that there will always be a phase difference of 180° between the outputs of a (second order) low-pass filter and a high-pass filter having the same crossover frequency. And so, in a 2-way system, the high-pass sections output is usually connected to the high frequency driver 'inverted', to correct for this phase problem. For passive systems, the tweeter is wired with opposite polarity to the woofer; for active crossovers the high-pass filter's output is inverted. In 3-way systems the mid-range driver or filter is inverted. However, this is generally only true when the speakers have a wide response overlap and the acoustic centers are physically aligned. Look up Phase in Wiktionary, the free dictionary Phase may refer to: Phase (matter), a physically distinctive form of a substance, such as the solid, liquid, and gaseous states of ordinary matter Phase (waves), the time position (or angle in the complex plane) within a cycle of a periodic waveform... The polarity of an object is, in general, its physical alignment of atoms. ...

Third order crossovers

3^rd order filters have a 60 dB/decade (or 18 dB/octave) slope. These crossovers usually have Butterworth filter characteristics; phase response is very good, the level sum being flat and in phase quadrature, similar to a first order crossover. The polar response is asymmetric. In the original D'Appolito MTM arrangement, a symmetrical arrangement of drivers is used to create a symmetrical off axis response when using 3rd order crossovers. The Butterworth filter is one type of electronic filter design. ... Phase response is the relationship between the phase of a periodic input and an ouput signal passing through any device which accepts an input and produces an output signal such as an amplifier or a filter. ... Look up quadrature in Wiktionary, the free dictionary. ... Symmetry is a characteristic of geometrical shapes, equations and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ...

Third order acoustic crossovers are often built from first or second order filter circuits.

Fourth order crossovers

4^th order filters have an 80 dB/decade (or 24 dB/octave) slope. These filters are complex to design in passive form. A 4^th order crossover with −6 dB crossover point and flat summing is also known as a Linkwitz-Riley crossover (named after its inventors). It can be constructed in active form by cascading two 2^nd order Butterworth filter sections. The output signals of this crossover order are in phase, thus avoiding phase inversion in driver connections unless the driver acoustic centers are not aligned. Magnitude plot of 2nd and 4th order Linkwitz-Riley filters A Linkwitz-Riley (L-R) filter is an infinite impulse response filter used in Linkwitz-Riley audio crossovers, named after its inventors Siegfried Linkwitz and Russ Riley, which was originally described in Passive Crossover Networks for Noncoincident Drivers in JAES... The Butterworth filter is one type of electronic filter design. ...

Higher order crossovers

Passive crossovers giving acoustic slopes higher than 4^th order are not common, because of cost and complexity. They are sometimes used in active crossover modules.

Mixed order crossovers

Crossovers can also be constructed with mixed order filters. For example, a second order lowpass combined with a third order highpass. These are generally passive and are used for several reasons, often when the component values are found by computer program optimization. A higher order tweeter crossover can sometimes help compensate for the time offset between the woofer and tweeter, caused by non aligned acoustic centers.

Classification based on circuit topology

Series and parallel crossover topologies. The HPF and LPF sections for the series crossover are interchanged with respect to the parallel crossover since they appear in shunt with the low & high frequency drivers.

Image File history File links Series_parallel_xover. ... Image File history File links Series_parallel_xover. ...

Parallel crossovers

These are by far the most common. Electrically the filters are in parallel and thus the various filter sections do not interact. This makes them easier to design because the sections can be considered separately, and because component tolerance variations will be isolated.

Series crossovers

Crossovers using this topology are almost always passive because it is easiest to construct in passive form. In this topology, the individual filters are connected in series, with a driver or driver combination connected in parallel to each filter. As can be seen in the image, a low-pass filter in shunt with the tweeter results in a high-pass response for the tweeter, since the lower frequencies are shunted by the LPF via the woofer. Similarly, the HPF in parallel with the woofer shunts away the higher frequencies via the tweeter - a low-pass response for the woofer. One advantage (or disadvantage, depending on how one looks at it) of this crossover, is that the crossover sections interact with each other. Changes in any one component affects both highpass and lowpass sections. To some extent, this makes the crossover somewhat self-balancing - the crossover frequency changes, but the system still sums substantially flat. This characteristic makes them appealing to designers not using using sophisticated measuring equipment or simulation software. These crossovers are also more sensitive to component tolerance variations. A shunt in general is a sort of relief valve, or diverter. ...

Derived Crossovers

These are active crossovers in which one of the crossover responses is derived from the other through the use of a differential amplifier. For example, the difference between the input signal and the output of the high pass section is a low pass response.^[1] Thus, when a differential amplifier is used to extract this difference, its output constitutes the low pass filter section. The main advantage of derived filters are that it produces no phase difference between the high pass and low pass sections at any frequency.^[2] The disadvantages are either

• (a) that the high pass and low pass sections often have different levels of attenuation in their stop bands, i.e. their slopes are asymmetrical,^[3] or
• (b) that the response of one or both sections peaks near the crossover frequency,^[4]

or both. In case (a), above, the usual situation is that the derived low pass response attenuates at a much slower rate than the fixed response. This requires the speaker to which it is directed to continue to respond to signals deep into the stopband where it's physical characteristics may not be ideal. In the case of (b), above, the both speakers are required to operate at higher volume levels as the signal nears the crossover points. This uses more amplifier power and may drive the speaker cones into non-linearity.

additional issues

Modern crossovers are increasingly also including a Zobel network which compensates for the characteristic changes in impedance with frequency essentially all drivers have. The issue is complex as part of the change in impedance is due to acoustic loading changes across a driver's passband. This article is considered orphaned, since there are very few or no other articles that link to this one. ...

Notes

1. ^ Bohn, D. (Ed.), Audio Handbook (National Semiconductor Corporation, Santa Clara, CA 1976) § 5.2.4
2. ^ Ibid.
3. ^ Ibid.
4. ^ See, Crawford, D., Constructing a Room Equalizer, Audio Magazine, Sept. 1972 p. 21, in which the slopes are symmetrical, and The Audio Pages, Subtractive Crossover Networks. http://sound.westhost.com/articles/derived-xovers.htm Retrieved August 11, 2007.

References

• DIY Audio at lalena.com - DIY Audio site with information on building crossovers. Includes a crossover calculator for 15 different types of crossovers.
• KS Digital German Loudspeaker Manufacturer (One of the first loudspeakers with digital crossovers)
• Article about active crossovers
• Comparison of active and passive crossovers
• Comparison of series and parallel crossovers
• Description of a L-R crossover
• Passive crossover design article
• ESP web-site
• Linkwitz Lab Crossovers
• Linkwitz-Riley Crossovers: A Primer
• Design of Digital Linear Phase FIR Crossover Systems
• Full-range Driver & Loudspeaker Theory
• http://www.audioholics.com/productreviews/loudspeakers/ThielSS2subwoofer.html
• Audioholics.com Filter & Crossover Types
• A Bessel Filter Crossover, and Its Relation to Others
• Active Lowpass Filter Design
• Second Order Low-pass Filter Responses

See also

• Full-range speaker
• Electrical characteristics of a dynamic loudspeaker