What are audio crossovers used for? Crossover for speakers: types and choice. What is a crossover and what do you eat it with?
Crossovers are devices in sound systems that create the desired operating frequency ranges for speakers. Speakers are designed to operate within a specific frequency range. They do not accept frequencies outside these limits. If a low frequency is applied to the high-frequency speaker (tweeter), the sound picture will deteriorate, and if the signal is also powerful, the tweeter will “burn out.” High-frequency speakers should only handle high frequencies, and woofers should only receive the low-frequency range from the overall audio signal. The remaining middle band goes to mid-range speakers (midwoofers). Therefore, the task of crossovers is to divide the audio signal into the desired (optimal) frequency bands for the corresponding types of speakers.
Simply put, a crossover is a pair of electrical filters. Let's say the crossover has a cutoff frequency of 1000 Hz. This means that one of its filters cuts off all frequencies below 1000 Hz and only allows frequencies above 1000 Hz to pass through. This filter is called a high-pass filter. Another filter that passes frequencies below 1000 Hz is called low-pass. Graphically, the operation of this crossover is shown in the figure. The point of intersection of the two curves is the crossover cutoff frequency equal to 1000 Hz. Three-way crossovers also have a mid-frequency filter (band-pass), which passes only the middle frequency range (approximately 600 Hz to 5000 Hz.) The figure shows the frequency response of a three-way crossover.
Order of sensitivity is the ratio of the output signal intensity (dB) of the crossover to the input signal frequency, assuming that the input signal intensity is constant. Typically, sensitivity (cutoff slope) is characterized as the ratio dB/octave. For many mathematical reasons, crossover sensitivity is always a multiple of 6 dB/octave. The first order crossover has a sensitivity of 6 dB/octave. The second order crossover has a sensitivity of 12 dB/octave, the third order has a sensitivity of 18 dB/octave, and the fourth order crossover sensitivity is 24 dB per octave.
Consider a third-order low-pass filter with a cutoff frequency of 100 Hz. As mentioned above, this crossover will only pass frequencies below 100 Hz, and will cut off frequencies above 100 Hz. Frequency cutting will occur as follows: all frequencies above 100 Hz will lose their intensity at the output of the filter by a multiple of 18 dB, depending on the octave they belong to. That is, the 200 Hz frequency (the first octave above the cutoff frequency) will lose its intensity by 18 dB, the intensity of the 400 Hz frequency (the second octave) will fall by 36 Hz, and the third octave (800 Hz) will attenuate by 54 dB. And so on, all subsequent octaves will be attenuated by a multiple of 18 dB. A less sensitive first-order low-pass filter with a cutoff frequency of 100 Hz will do the same thing, only unnecessary octaves will be attenuated not by 18 dB, but by 6 dB.
As you can see, the filters that make up the crossovers cannot immediately cut off unnecessary frequencies, but do it gradually, with different sensitivities depending on their order.
First-order crossovers are the simplest passive crossover, which consists of one capacitor and one inductor. The capacitor acts as a high-pass filter to protect the tweeter from unnecessary low and mid frequencies. The coil is used as a low-pass filter. The sensitivity of first-order crossovers is low - only 6 dB per octave. A positive feature of these crossovers is the absence of phase shift between the tweeter and the other speaker.
Crossovers of the second order. They are also called Butterworth crossovers, named after the creator of the mathematical model of these crossovers. Structurally, they consist of one capacitor and coil on the tweeter and one capacitor and coil on the woofer. They have a higher sensitivity of 12 dB per octave, but give a phase shift of 180 degrees, which means that the tweeter and other speaker membranes are not synchronized. To fix this problem, you need to change the polarity of the wires on the tweeter.
Crossovers of the third order. Such crossovers have one coil and two capacitors on the tweeter, while the opposite is true on the low-frequency speaker. The sensitivity of such crossovers is 18 dB per octave, and they have good phase characteristics in any polarity. The downside to third-order crossovers is that they cannot use time delays to correct problems associated with speakers not emitting on the same vertical plane.
Crossovers of the fourth order. Fourth-order Butterworth crossovers have a high sensitivity of 24 dB per octave, which dramatically reduces the interference of speakers in the frequency separation region. The phase shift is 360 degrees, which actually means there is no phase shift. However, the magnitude of the phase shift in this case is not constant and can lead to unstable operation of the crossover. These crossovers are practically never used in practice.
Linkwitz and Riley managed to optimize the design of the fourth-order crossover. This crossover consists of two second-order Butterworth crossovers connected in series for the tweeter, and the same for the woofer. Their sensitivity is also 24 dB per octave, but the output level of each filter is 6 dB less than the crossover output level. The Linkwitz-Riley crossover has no phase shifts and allows time correction for speakers that do not operate in the same physical plane. These crossovers provide the best acoustic performance compared to other designs.
Passive Crossover Design
As mentioned above, a passive crossover consists of capacitors and inductors. In order to assemble a first-order passive crossover, you need to have one capacitor and one inductor. The capacitor is installed in series with the tweeter (high-pass filter), and the coil is installed in series with the woofer (low-pass filter). The nominal values of inductance ((H - microhenry) and capacitance ((F - microfarads)) are given in the table depending on the desired crossover cutoff frequency and speaker impedance.
First order crossover (6 dB/octave)
For example, let’s select capacitance and inductance for a crossover with a cutoff frequency of 4000 Hz and a speaker impedance of 4 ohms. From the above table we find that the capacitance of the first order capacitor should be equal to 10 mF, and the inductance of the coil should be 0.2 mH.
To determine the nominal values of the components for a second-order crossover (12 dB/octave), it is necessary to multiply the values from the same table for the capacitor by a factor of 0.7, and multiply the value for the inductor by a factor of 1.414. We must remember that for a second-order crossover, two capacitors and two inductors are needed. Let's create a second-order crossover for a cutoff frequency of 4000 Hz. To determine the values for both capacitors, multiply the value from the table 10 mF by a factor of 0.7 and get 7 mF. Next, we multiply the inductance value of 0.2 mH by a coefficient of 1.414 and get an inductance value of 0.28 mH for each coil. One of these capacitors is installed in series on the tweeter, and the second in parallel on the woofer. One coil is in parallel for the tweeter, and the other is in series for the woofer.
Passive and active crossovers
The difference between these two types of crossovers is very simple. An active crossover requires an external power supply, while a passive crossover does not. Because of this, an active crossover takes place in the sound system before the amplifier, processing the audio signal from the preamplifier of the head unit (for example, a car radio). Next, after the active crossover, two or three power amplifiers are installed. In this case, one amplifier is not installed, since there is no point in combining the signals separated by an active crossover into a single signal in the amplifier. The separated signals must be amplified separately. As you can see, active crossovers are used in expensive high-quality sound systems.
Passive crossovers process an already amplified signal and are installed in front of the speakers. The capabilities of passive crossovers are limited compared to active ones, but their correct use can give good results with minimal financial costs. Passive crossovers perform well when order of magnitude sensitivity requirements are less than 18 dB per octave. Above this limit, only active crossovers work well.
Passive crossovers are mainly used to process the signal of tweeters and midrange speakers. These crossovers can be used for low-frequency speakers, but the demand for the quality of capacitors and inductors sharply increases, which leads to their rise in price and increase in size. Passive crossovers do not tolerate overloads well. Peak signal intensities coming from the amplifier can change the cutoff frequency of the filters. In addition, an overloaded filter weakens the audio signal (damping). Therefore, when choosing passive crossovers, pay attention to their ability to withstand peak loads created by the amplifier.
Active (or electronic) crossovers are a variety of active filters that can be controlled and easily change the cutoff frequency of any channel. The sensitivity of active crossovers can be any order, from 6 dB to 72 dB per octave (and higher). Basically, active crossovers for car audio systems have a sensitivity of 24 dB per octave. With such sensitivity, frequency exchange between speakers is practically eliminated. The sound picture is very high quality. The only drawback of active crossovers is their high cost compared to passive ones.
Phase shift
Now let's talk about phase shifts that can occur in sound systems that use crossovers. Phase shift is an inevitable phenomenon resulting from the design features of high-pass, low-pass and band-pass filters.
Phase is the temporal relationship between two signals. The phase is measured in degrees from 0 to 360. If two identical speakers emit sound waves in opposite phase (180 degree phase shift), then the sound is attenuated. The problem is resolved by changing the polarity on one of the speakers.
When the acoustic system consists of different speakers operating in different frequency ranges (tweeter and midwoofer), then eliminating the phase shift is not always solved by simply changing “+” to “-“. The wavelength from the tweeter is shorter than from the midwoofer. Therefore, the high-frequency wave front may reach the listener later (or earlier) than the mid-frequency (or low-frequency) wave front. This time delay is a consequence of the phase shift. In this case, the sound picture can be optimized by physically aligning the two speakers relative to each other in the vertical plane until the sound picture is improved. For example, at a wave frequency of 1000 Hz, a time delay of one millisecond is eliminated by moving the speakers relative to each other by 30 cm.
Setting up an active crossover
The most important thing in setting up a crossover is choosing the right cutoff frequency. If we have a three-way active crossover, then we are faced with the task of determining two cutoff points (frequencies). The first point determines the cutoff frequency for the subwoofer (low-pass) and the beginning of the mid-frequency range for the midwoofer (high-pass). The second point determines the end frequency of the mid-range (low-pass) and the starting frequency of the high-frequency range for the tweeter (high-pass). The most important thing is that when setting crossover cutoff frequencies, remember the frequency characteristics of the speaker and under no circumstances load the speaker with frequencies that are not within its operating range.
For example, if the subwoofer rattles a little or makes a hum, it means it is overloaded with unwanted mid frequencies (above 100 Hz). Move the cutoff frequency (low-pass) to 75 Hz and/or set the sensitivity to 18 dB or 24 dB per octave, if possible. Let us recall that increasing the order of the crossover sensitivity (dB/octave value) cuts off unnecessary frequencies more efficiently, preventing them from leaking through the filter. The sensitivity of high-pass filters for a midwoofer can be left at 12 dB/octave (for “soft” mid-frequency speakers). This active crossover setup is called asymmetrical.
This table shows the starting cutoff frequencies for various types of speakers when configuring active crossovers.
What is a crossover and why is it needed?Before answering this question, it is first necessary to take a short detour into loudspeaker theory and outline the problem. As is known, almost any speaker currently produced is capable of effectively reproducing only a narrow frequency band, limited from below by the resonant frequency of its moving system, and from above by the mechanical properties of the diffuser (weight, rigidity). Beyond the boundaries of this frequency band, the sound pressure created by the speaker decreases significantly and the level of distortion increases. We can't talk about high-quality sound here. Therefore, to transmit the full spectrum of audio signals (20-20,000 Hz), it is necessary to use several speakers. Long ago, acousticians realized this need, and today in all areas of audio technology, be it home or automotive systems, the vast majority of speaker systems are implemented exclusively using a multi-driver design.
In relation to car audio systems, two fairly typical construction schemes can be distinguished, with which even more or less informed readers are familiar. The first and most common consists of three speakers: a subwoofer aimed exclusively at bass (approximately 20-100 Hz), a woofer/midrange speaker for the upper bass and mid-frequency ranges (100-3000 Hz), and a tweeter responsible for high frequencies (from 3000 Hz). Hz and higher). In more complex designs, such as those presented by professionals in car audio competitions, the number of speakers increases. Here, separate speakers are responsible for each frequency range: lower bass, mid/upper bass, mids and highs. But, despite the obvious differences, both schemes are subject to the same requirement: each speaker included in the speaker system must reproduce only its own frequency band and not affect neighboring ones. To fulfill this requirement, electrical filters are included in the audio path, which are responsible for highlighting some frequency bands and suppressing others. Obviously, if an acoustic system uses several speakers - a subwoofer, a bass/midrange driver, a midrange driver and a tweeter, there is a need to use several electrical filters. The combination of several such filters is called a crossover.
Filters
To a first approximation, any electrical filter is a combination of several elements that have the property of selectively transmitting signals of certain frequencies. The simplest circuits that have similar properties can be built using inductors and capacitors. The principle of operation of these circuits is based on the dependence of the resistance of the elements included in their composition on frequency: for inductors, the resistance increases with increasing frequency of the signal, and for capacitors, on the contrary, it decreases. Therefore, inductors pass low frequencies well, and capacitors pass high frequencies. These properties are used to construct filters - low-pass (LPF) and high-pass (HPF). In addition to low-pass filters and high-pass filters, there are other types of filters, for example, bandpass - in other words, bandpass. From the name it is clear that such filters transmit well only a certain frequency band, and everything that is beyond it is suppressed by a bandpass filter (BF). The usual role of such filters is to isolate the mid-frequency range for subsequent feeding of the filtered signal to the midrange speaker. According to the task being performed, the next type of filter is a notch filter (RF) - the exact opposite of PF. The band of frequencies that the PF passes through without changes is suppressed by the notch filter, opening free access to signals outside this frequency range. Somewhat different from all the above types of filters are infra-low frequency suppression filters (FINCH); in essence, these are the same high-pass filters, but with an extremely low cutoff frequency (10-30 Hz). The purpose of the FINCH is to protect the low-frequency head (subwoofer) from infra-low frequency signals, which can lead to overload of the subwoofer, and sometimes to its failure.
Each filter is characterized by several parameters. The first parameter of the filter is its order. The filter order corresponds to the number of reactive elements in the circuit (inductors, capacitors). A first order filter, as the name suggests, contains only one reactive element. A second-order filter contains two elements, etc. Another filter indicator is directly dependent on the order - the slope of the amplitude-frequency response. This parameter shows how sharply the filter attenuates signals outside the passband, that is, signals of those frequencies that should not overcome the filter barrier and reach the speaker. The slope is measured in decibels per octave (dB/oct). An octave is a frequency band in which the upper limit frequency is twice the lower frequency. For example, an octave can be considered frequency intervals from 100 to 200 Hz or from 200 to 400 Hz. It is easy to calculate that the entire range of sound signals (20-20,000 Hz) contains approximately ten octaves. The second unit of measurement is the decibel, named after the inventor of the telephone, A. G. Bell; this is the logarithm of the ratio of quantities (in this case, the filter's transmission coefficients at the cutoff frequencies of the octave), showing the relative difference between these quantities. A difference of 6 dB means that the levels differ by a factor of two, 12 dB by a factor of four, 20 dB by a factor of ten, etc. Now, returning to the slope of the amplitude-frequency response, we note that numerically it is directly proportional to the order filter and equals 6*N, where N is the order of the filter. Obviously, the slope of the first-order filter is 6 dB/oct, the second - 12 dB/oct, the third - 18 dB/oct, etc., and the higher it is, the more effectively the filters are able to suppress unnecessary signals. When choosing a filter order, along with the shape of the amplitude-frequency characteristic, it is necessary to take into account the phase-frequency characteristic. An ideally operating crossover should provide a uniform total frequency response in terms of sound pressure, which is summed up from the vibrations created by all heads of the speaker system. When summing, both amplitude and phase relationships appear, as well as the location of the heads in relation to the listener. The optimal result is ensured by using filters of a very specific order. Interested readers can find more detailed information on this matter, for example, in the book “Radio Broadcasting and Electroacoustics” edited by Yu. A. Kovalgin, published by the publishing house “Radio and Communications” in 1999.
At the same time, the filter function is characterized not only by the order and steepness of the frequency response decline. The approximation method on the basis of which its transfer function is determined can tell a lot about the nature of the filter. There are a lot of such methods today, and they all bear the names of their creators: Butterworth, Bessel, Linkwitz-Ralley and many others. It would seem that the large number of methods means many design differences in the implementations of filters even of the same order, but nothing like that. The reactive elements that can be seen on the electrical circuits of Butterworth, Bessel, Linkwitz-Ralley filters of the same order are the same, but the ratings of these elements are significantly different, which means different behavior of the amplitude and phase-frequency characteristics of the filters. As a result, the timing characteristics are also different.
In general, all types of filters are divided into two more fairly broad classes - active and passive, and accordingly, the crossovers that include these filters can be passive and active.
Passive crossovers consist solely of reactive elements - inductors and capacitors, and do not require power. They are very undemanding, and under certain conditions they can be included in any part of the path, both before and after the power amplifier. But most often, passive crossovers are allocated a strictly defined area - between the power amplifier and the speakers. Using a crossover, it is possible to connect several heads operating in adjacent frequency bands to one amplifier. Cheap and cheerful! But there are also shadow sides. The presence of a crossover on the path between the power amplifier and the loudspeaker leads to the fact that up to ten percent of the useful energy is dissipated on the reactive elements and matching resistors. However, this is far from the only drawback of passive crossovers. We should also not forget that they have very limited capabilities for adjusting the sound, most often limited to level controls for individual frequency bands. The characteristics of passive filters depend significantly on the load resistance, which is the electrical resistance of the loudspeaker. In the operating frequency range it is very unstable, therefore optimal matching conditions cannot be ensured, and the frequency response of the filters differs from the calculated one. This also cannot be attributed to the advantages of passive crossovers.
Active crossovers in the service of automotive power amplifiers
If all the filter circuits currently used in audio equipment were built on passive elements, then most likely, over time, the copper reserves on planet Earth would be under threat. Why? Yes, because the manufacture of even the simplest first-order low-pass filter with a low cutoff frequency (100 Hz) based on an inductor requires a lot of copper wire, and not just simple, but the most serious: large cross-section, with low losses and high quality. It is unknown what we would be faced with today if several decades ago electronics specialists had not invented active filters, where bulky inductors and capacitors were replaced by electronic elements - transistors and operational amplifiers, which, when turned on in a certain way, in combination with resistors and capacitors have the same properties as LC circuits - identical phase shift between current and voltage and dependence of the transmission coefficient on frequency.
The appearance of fundamentally new filter circuits, like any other innovation in audio technology, immediately caused a lot of controversy. The main wave of criticism arose from the ranks of real audiophiles, who unanimously argued that active filters that require supply voltage are a serious obstacle to natural, natural sound. In this they were partly right, but the wide list of advantages of the newly introduced filters became a powerful argument in their favor. And soon these filters began to be actively used in built-in crossovers of car amplifiers. Such crossovers are usually located inside the amplifier housing, and their place in the signal path is at the input, immediately after the input sensitivity control circuits, before the pre-amplification circuits. It must be said that an important role in this transformation was played by the possibility of implementing active filters in minimalist dimensions, which remains a utopia for passive analogues to this day.
In budget amplifier models, built-in crossovers are based on identical filter units. This type of filter is a simplified variation of the Bessel filter; it is very simple to manufacture, because, unlike Linkwitz-Ralley, Bessel and Butterworth filters, it is built on elements of the same nominal value and is not particularly critical to tolerances for parameter deviations, which can sometimes reach many tens of percent. It is obvious that the amplitude and phase frequency characteristics of such filters are far from perfect, to say the least - they are the worst. The next pitfall that can be encountered in the design of budget-level built-in crossovers is related to the organization of the choice of crossover frequency. To reduce the cost of a crossover, many manufacturers deliberately minimize the number of tuning elements, and as a result, only one link of a second-order filter is tuned in frequency. It is clear that in this case it is quite difficult to talk about the stability of the crossover characteristics over the entire range of settings.
In mid- and high-price amplifiers, crossovers are most often implemented based on Linkwitz-Ralley, Butterworth and Bessel filters - second, third, and less often fourth order. Each of them has its own advantages and disadvantages, but, other things being equal, it is generally accepted that Butterworth filters have minimal frequency response unevenness, and Bessel filters have a phase response. In this class of amplifiers, to ensure precise adjustment of the cutoff frequency, many reputable manufacturers have adopted the so-called “click” method. Its essence is that the cutoff frequency of the high-pass filter and low-pass filter is adjusted according to a special “click-frequency” correspondence table, where, for example, the extreme left position of the potentiometer can correspond to a cutoff frequency of 20 Hz, the next - 22 Hz, etc., and the latter - five, and sometimes ten kilohertz. This tuning method is distinguished by very high accuracy of the result; it is found in amplifiers "PPI" and "Orion", etc.
A slightly different approach to setting the cutoff frequency is demonstrated by amplifiers produced by the Italian companies "Steg", "Audiosystem", as well as a number of other companies. Here, the desired cutoff frequency is selected by installing one or another resistive module-chip. This method is less universal than the one described above, however, it promises good results. A logical continuation of this approach are crossovers, in which the cutoff frequency is limited to a few fixed values. This is a fairly common solution, often found in high-end amplifiers. A good example is the many high end amplifiers from McIntosh. Here, the cutoff frequency of both filters - the high-pass filter and the low-pass filter - is fixed, and is limited to two values - 80 and 120 Hz. By the way, using these amplifiers as an example, we can demonstrate the use of notch filters in built-in crossovers. In them, the notch filter is tuned to the average resonance frequency of the car interior (150 Hz) and, to some extent, allows you to correct a possible rise in the amplitude-frequency response.
A special group consists of crossovers, in which you can adjust not only the cutoff frequency of a particular filter, but in addition also the slope of the amplitude-frequency response. Such broad capabilities are in themselves a rarity, but the Japanese “hDimension” amplifiers from the “Forte” series can boast of them, in which the maximum possible value of the slope of the attenuation characteristic reaches 48 dB/oct.
Sometimes in the low-frequency section of built-in crossovers you can find a high-pass filter with an adjustable quality factor, which allows you to increase the frequency response near the cutoff frequency up to 10 dB (Hawkins circuit). This circuit design is often found in Soundstream amplifiers; it allows you to exclude a separate stage of the bass boost circuit from the settings path.
The implementation of infra-low frequency suppression filters in built-in crossovers clearly demonstrates the advantages of active filtering. Such a filter on the board of many amplifiers takes up an insignificant area, but at the same time allows you to adjust the cutoff frequency in the range from 15 to 50 Hz, and with a slope of the attenuation characteristic from 18 to 24 dB/oct. True, some manufacturers sometimes deliberately reduce customization options, limiting themselves to a few fixed, typical values. As practice shows, this is more than enough.
Conclusion
After reading this review, many readers will probably want to ask a very reasonable question: is the use of a built-in crossover in car power amplifiers justified or is it just another way of withdrawing “hard-earned” funds? In many ways, the answer to this question depends on the level of the amplifier. If the device belongs to the budget or entry-level class, then it would certainly be naive to hope that the built-in crossover will not make significant changes to the signal. It's another matter when the amplifier belongs to the middle, or even elite class. Here manufacturers are playing by different rules. The credibility of the company is at stake, and the use of poor separation filters, as well as other elements, can damage its prestige. It is quite obvious that in this case you can seriously think about using an amplifier crossover, especially since high-end amplifiers usually have very good capabilities. Naturally, such a solution will lead to the construction of an audio system based on the principle of multi-band amplification (bi-amping), which does not help save the budget, because at least four amplification channels will be needed.
An acoustic crossover is an element that allows you to adjust the sound of speakers, separate and equalize frequency ranges. You can buy it, ask someone to install it, but most often there is no desire to spend money on it. It’s better to install a new speaker system completely, to create a real sound stage. It's not difficult, but it's expensive.
Crossover for acoustics
Many people want to save a lot of money and do a comprehensive tuning of their car. This dream is tempting, no doubt. If an opportunity arises, we must act. However, this dream rarely comes true. There are other needs. No time for music. Until the required amount for all additions and transformations accumulates, the car can stop driving. Urgent problems must be resolved in a timely manner. If it's winter outside, it's time to change your tires. If the speakers sound different, it’s time to adjust it. Hoping to win a million, a billion, a trillion is commendable. The main thing is to correspond to reality.
Do-it-yourself acoustic crossover – is it real or not? Many people claim that assembling it yourself is easier than it seems. And it’s much cheaper, plus it’s an interesting process. You just need to want to do it, set a goal for yourself, delve into the essence of the issue, figure it out, and objectively assess your capabilities. At first glance, it is difficult to assemble a crossover for acoustics with your own hands. But this is only at first glance.
Another obstacle is that you don’t want to spoil the appearance of the interior. What should you do: take the risk of doing such work yourself or give up your dream? Of course, this is a difficult choice, a dilemma. On the other hand, no matter what, the appearance of the interior will always be corrected at the service station.
When exactly is this element needed?
Good acoustics may not need a crossover at all. Why? Because the frequency range of the sound entering the speakers is harmonious. The speakers themselves and other elements contribute to this. However, even a good acoustic system, which is expensive, sometimes does not satisfy with its sound. An ear for music is not a vice. Is it worth suffering because of an innate biological feature? The manufacturer is not obliged to focus on the category of citizens with an ear for music and sensitive receptors.
Speakers without a crossover are not functional in some cases. What is it: creaks, extraneous noise, voice distortion? A good trainer for hearing and strengthening the nervous system? Taking care of yourself is important. Manufacturers sometimes offer people to do this themselves.
Music is many sounds that have different frequency ranges. Some people hear, some they don’t. He likes some, he doesn't like others. Muting certain frequencies, on the contrary, emphasizing them, making them loud or completely unnoticeable - the crossover was invented for this purpose. Acoustics will delight and truly serve people if this element is added.
If it doesn't work out the first time
Even if the first attempt to find the necessary materials or tools is not crowned with success, you should put your idea aside for later, but not say goodbye to it. It's really easy to take and make a crossover. A crossover diagram for acoustics and a photo of the device in detail will help with this. It’s easy to understand, understand what it is in principle, get a visual representation, and make a decision based on the facts.
These photos clearly show that there is nothing wrong with the device. It's as simple as 5 kopecks. Both the girl and the man who attended physics classes at school and studied diligently will cope. However, you can buy a ready-made, factory-made crossover, or entrust tuning and modernization of the car's acoustic system to professionals. It just costs money.
Types of crossover
What kind of crossovers are there? There are not so many of them:
- active;
- passive;
- single-lane;
- two-way;
- three-way.
The diagram of each type will contain different elements. A passive crossover consists of coils, relays and capacitors. Its scheme is simpler. There are no boards or microcircuits in it, and it’s easier to make it yourself than an active one. Their installation scheme is also different.
The number of bands is determined by the number of bands in the acoustics, corresponding. Three-way crossovers must be connected to three-way speaker systems. A two-way speaker system and three-way crossovers, for example, are incompatible concepts. So, if the car has two-way speakers installed, there is nothing left to do but replace it or install three-way crossovers. Two-way speakers and one-way crossovers are also a bad combination. Three-way systems and one-way crossover are similar. The rule of complementarity rules here. But if you need an active or passive crossover, you can choose without thinking too much.
A passive crossover will make the system work well, although it has a number of disadvantages. It is believed that acoustics with a passive crossover will not work 100%. And this is true, because an active crossover for acoustics is more powerful. On the other hand, you need a fairly deep knowledge of physics in order to assemble an active crossover with your own hands.
It seems that the time has come to choose what you want more: for the acoustics to work at full capacity or for the sound to be acceptable. In fact, this is not entirely true. Even an active crossover can be assembled with your own hands, it just may not work out right away. As they say in such cases, patience and work will grind everything down.
A passive crossover lasts less time. So, it’s worth thinking about it, weighing the pros and cons before you start working.
What is crossover calculation
The crossover circuit may still force you to refuse to assemble the part yourself. But even the diagram will not force you to give up the prospect of installing the purchased crossover yourself. This is a modernization from the elementary category. Why not? Calculating the crossover for acoustics is the main problem. The easiest way is to use an online calculator. The calculation will be fairly accurate, although there is a possibility of errors and the result may not be satisfactory. The car speaker system will still produce the same noise, not music. What's the catch?
If you try to perform the calculation without a calculator, everything will fall into place. But not in the sense that the car audio system will immediately, as if by magic, start working well. It becomes clear that an individual approach and crossover tuning is needed.
What we know about speakers is that they have frequency, power, and impedance. The values are individual and depend on the brand and model. Calculating a crossover means knowing the resistance and frequency. It just works in theory. In practice, a person faces such a problem as instability of the resistance value. Resistance is not a constant. As the frequency changes, so does the resistance. Therefore, you need to know, at least in what range the car speaker system operates, the arithmetic average. For this you need special devices. Otherwise there is no way to know these values. Expectations should not be too high.
Crossovers- these are devices in sound systems that create the required operating frequency ranges for speakers. Speakers are designed to operate within a specific frequency range. They do not accept frequencies outside these limits. If a low frequency is applied to the high-frequency speaker (tweeter), the sound picture will deteriorate, and if the signal is also powerful, the tweeter will “burn out.” High-frequency speakers should only handle high frequencies, and woofers should only receive the low-frequency range from the overall audio signal. The remaining middle band goes to mid-range speakers (midwoofers). Therefore, the task of crossovers is to divide the audio signal into the desired (optimal) frequency bands for the corresponding types of speakers.
Simply put, crossover is a pair of electrical filters. Let's say the crossover has a cutoff frequency of 1000 Hz. This means that one of its filters cuts off all frequencies below 1000 Hz and only allows frequencies above 1000 Hz to pass through. This filter is called a high-pass filter. Another filter that passes frequencies below 1000 Hz is called low-pass.
The point of intersection of the two curves is the crossover cutoff frequency equal to 1000 Hz. Three-way crossovers also have a mid-frequency filter (band-pass), which passes only the middle frequency range (approximately 600 Hz to 5000 Hz.) The figure shows the frequency response of a three-way crossover.
Order of sensitivity is the ratio of the output signal intensity (dB) of the crossover to the input signal frequency, assuming that the input signal intensity is constant. Typically, sensitivity (cutoff slope) is characterized as the ratio dB/octave. For many mathematical reasons, crossover sensitivity is always a multiple of 6 dB/octave. The first order crossover has a sensitivity of 6 dB/octave. The second order crossover has a sensitivity of 12 dB/octave, the third order has a sensitivity of 18 dB/octave, and the fourth order crossover sensitivity is 24 dB per octave.
Consider a third-order low-pass filter with a cutoff frequency of 100 Hz. As mentioned above, this crossover will only pass frequencies below 100 Hz, and will cut off frequencies above 100 Hz. Frequency cutting will occur as follows: all frequencies above 100 Hz will lose their intensity at the output of the filter by a multiple of 18 dB, depending on the octave they belong to. That is, the 200 Hz frequency (the first octave above the cutoff frequency) will lose its intensity by 18 dB, the intensity of the 400 Hz frequency (the second octave) will fall by 36 Hz, and the third octave (800 Hz) will attenuate by 54 dB. And so on, all subsequent octaves will be attenuated by a multiple of 18 dB. A less sensitive first-order low-pass filter with a cutoff frequency of 100 Hz will do the same thing, only unnecessary octaves will be attenuated not by 18 dB, but by 6 dB.
As you can see, the filters that make up the crossovers cannot immediately cut off unnecessary frequencies, but do it gradually, with different sensitivities depending on their order.
Capacitors are the simplest crossovers for channel-by-channel inclusion. We connect midbass to one pair of channels directly, and tweeters to another pair of channels through capacitors. In most cases, their capacitances are on the order of 3–5 μF.
Crossovers of the first order- This is the simplest passive crossover, which consists of one capacitor and one inductor.
The capacitor acts as a high-pass filter to protect the tweeter from unnecessary low and mid frequencies. The coil is used as a low-pass filter.
The sensitivity of first-order crossovers is low - only 6 dB per octave. A positive feature of these crossovers is the absence of phase shift between the tweeter and the other speaker.
Second-order crossovers. They are also called Butterworth crossovers, named after the creator of the mathematical model of these crossovers. Structurally, they consist of one capacitor and coil on the tweeter and one capacitor and coil on the woofer.
They have a higher sensitivity of 12 dB per octave, but give a phase shift of 180 degrees, which means that the tweeter and other speaker membranes are not synchronized.
To fix this problem, you need to change the polarity of the wires on the tweeter.
Third-order crossovers. Such crossovers have one coil and two capacitors on the tweeter, while the opposite is true on the low-frequency speaker.
The sensitivity of such crossovers is 18 dB per octave, and they have good phase characteristics in any polarity.
The downside to third-order crossovers is that they cannot use time delays to eliminate problems associated with speakers not emitting on the same vertical plane.
Fourth-order crossovers. Fourth-order Butterworth crossovers have a high sensitivity of 24 dB per octave, which dramatically reduces the interference of speakers in the frequency separation region. The phase shift is 360 degrees, which actually means there is no phase shift. However, the magnitude of the phase shift in this case is not constant and can lead to unstable operation of the crossover. These crossovers are practically never used in practice.
Linkwitz and Riley managed to optimize the design of the fourth-order crossover. This crossover consists of two second-order Butterworth crossovers connected in series for the tweeter, and the same for the woofer. Their sensitivity is also 24 dB per octave, but the output level of each filter is 6 dB less than the crossover output level. The Linkwitz-Riley crossover has no phase shifts and allows time correction for speakers that do not operate in the same physical plane. These crossovers provide the best acoustic performance compared to other designs.
Designing Passive Crossovers
As mentioned above, a passive crossover consists of capacitors and inductors. In order to assemble a first-order passive crossover, you need to have one capacitor and one inductor. The capacitor is installed in series with the tweeter (high-pass filter), and the coil is installed in series with the woofer (low-pass filter). Nominal values for inductance ((H - microhenry) and capacitance ((F - microfarad) are given in the table depending on the desired crossover cutoff frequency and speaker impedance.
For example, let’s select capacitance and inductance for a crossover with a cutoff frequency of 4000 Hz and a speaker impedance of 4 ohms. From the above table we find that the capacitance of the first order capacitor should be equal to 10 mF, and the inductance of the coil should be 0.2 mH.
To determine the nominal values of the components for a second-order crossover (12 dB/octave), it is necessary to multiply the values from the same table for the capacitor by a factor of 0.7, and multiply the value for the inductor by a factor of 1.414. We must remember that for a second-order crossover, two capacitors and two inductors are needed. Let's create a second-order crossover for a cutoff frequency of 4000 Hz. To determine the values for both capacitors, multiply the value from the table 10 mF by a factor of 0.7 and get 7 mF. Next, we multiply the inductance value of 0.2 mH by a coefficient of 1.414 and get an inductance value of 0.28 mH for each coil. One of these capacitors is installed in series on the tweeter, and the second in parallel on the woofer. One coil is in parallel for the tweeter, and the other is in series for the woofer.
Passive and active crossovers
The difference between these two types of crossovers is very simple. An active crossover requires an external power supply, while a passive crossover does not. Because of this, an active crossover takes place in the sound system before the amplifier, processing the audio signal from the preamplifier of the head unit (for example, a car radio). Next, after the active crossover, two or three power amplifiers are installed. In this case, one amplifier is not installed, since there is no point in combining the signals separated by an active crossover into a single signal in the amplifier. The separated signals must be amplified separately. As you can see, active crossovers are used in expensive high-quality sound systems.
Passive crossovers process an already amplified signal and are installed in front of the speakers. The capabilities of passive crossovers are limited compared to active ones, but their correct use can give good results with minimal financial costs. Passive crossovers perform well when order of magnitude sensitivity requirements are less than 18 dB per octave. Above this limit, only active crossovers work well.
Passive crossovers are mainly used to process the signal of tweeters and midrange speakers. These crossovers can be used for low-frequency speakers, but the demand for the quality of capacitors and inductors sharply increases, which leads to their rise in price and increase in size. Passive crossovers do not tolerate overloads well. Peak signal intensities coming from the amplifier can change the cutoff frequency of the filters. In addition, an overloaded filter weakens the audio signal (damping). Therefore, when choosing passive crossovers, pay attention to their ability to withstand peak loads created by the amplifier.
Active (or electronic) crossovers are a variety of active filters that can be controlled and easily change the cutoff frequency of any channel. The sensitivity of active crossovers can be any order, from 6 dB to 72 dB per octave (and higher). Basically, active crossovers for car audio systems have a sensitivity of 24 dB per octave. With such sensitivity, frequency exchange between speakers is practically eliminated. The sound picture is very high quality. The only drawback of active crossovers is their high cost compared to passive ones.
Phase shift
Now let's talk about phase shifts that can occur in sound systems that use crossovers. Phase shift is an inevitable phenomenon resulting from the design features of high-pass, low-pass and band-pass filters.
Phase is the temporal relationship of two signals. The phase is measured in degrees from 0 to 360. If two identical speakers emit sound waves in opposite phase (180 degree phase shift), then the sound is attenuated. The problem is resolved by changing the polarity on one of the speakers.
When the acoustic system consists of different speakers operating in different frequency ranges (tweeter and midwoofer), then eliminating the phase shift is not always solved by simply changing “+” to “-“. The wavelength from the tweeter is shorter than from the midwoofer. Therefore, the high-frequency wave front may reach the listener later (or earlier) than the mid-frequency (or low-frequency) wave front. This time delay is a consequence of the phase shift. In this case, the sound picture can be optimized by physically aligning the two speakers relative to each other in the vertical plane until the sound picture is improved. For example, at a wave frequency of 1000 Hz, a time delay of one millisecond is eliminated by moving the speakers relative to each other by 30 cm.
Setting up an active crossover
The most important thing in setting up a crossover is choosing the right cutoff frequency. If we have a three-way active crossover, then we are faced with the task of determining two cutoff points (frequencies). The first point determines the cutoff frequency for the subwoofer (low-pass) and the beginning of the mid-frequency range for the midwoofer (high-pass). The second point determines the end frequency of the mid-range (low-pass) and the starting frequency of the high-frequency range for the tweeter (high-pass). The most important thing is that when setting crossover cutoff frequencies, remember the frequency characteristics of the speaker and under no circumstances load the speaker with frequencies that are not within its operating range.
For example, if the subwoofer rattles a little or makes a hum (unpleasant resonance of the car body), then it is overloaded with unwanted mid frequencies (above 100 Hz). Move the cutoff frequency (low-pass) to 75 Hz and/or set the sensitivity to 18 dB or 24 dB per octave, if possible.
Let us recall that increasing the order of the crossover sensitivity (dB/octave value) cuts off unnecessary frequencies more efficiently, preventing them from leaking through the filter. The sensitivity of high-pass filters for a midwoofer can be left at 12 dB/octave (for “soft” mid-frequency speakers). This active crossover setup is called asymmetrical.
Homemade crossover for acoustics
Homemade crossovers for acoustics are needed to separate the frequency ranges of the speakers. They equalize these same ranges according to sound volume.
Making a homemade crossover for acoustics is not so difficult if you know some secrets.
What is a crossover and what do you eat it with?
First, let’s find out why we need a crossover?
This is a special device designed to separate audio frequencies. Crossovers seem to remove unnecessary frequencies and filter them.
For example, there are speakers (see) like tweeters. If there were no crossovers, then all frequencies, their full package, along with low frequencies and midrange frequencies, would be supplied to the tweeters. It is clear that this will ultimately negatively affect the detail of the music.
HF speakers, such as tweeters, are not capable of reproducing low and medium sounds and the presence of unusual frequencies will become a dangerous problem in this case.
Types of crossovers
Crossovers are usually divided into active and passive, as well as single-way, two-way, etc.
Passive crossover, its pros and cons
So:
- A passive crossover filters the signal with its capacitors, resistors and coils. As a result of this, the first drawback of such crossovers is revealed - loss of power.
- Passive crossovers are connected directly in front of the speakers. It turns out that it is enough to use just one amplifier (see), which is an undoubted advantage of passive crossovers.
- Passive crossovers are sold individually or as a set with speakers, usually two-way or more.
- Among the disadvantages of passive crossovers, one can highlight the limited peak load, which entails rapid failure.
Active crossover, its pros and cons
So:
- An active crossover is used in front of the amplifier. Therefore, using one amplifier in this case is simply impossible.
In the case of an active crossover, each speaker, be it a tweeter or a woofer, uses a separate amplifier channel.
- The advantage of an active crossover is that, unlike a passive one, it allows you to fine-tune the cuts. It is this factor that largely determines the cost of such a crossover, which is more expensive than its opponent.
Single-way crossover
- Designed to cut the subwoofer channel (see).
Two-way crossover
- Designed for two-way acoustics consisting of a tweeter and midbass.
Three-way crossover
- Designed for three-way acoustics consisting of a tweeter, midrange speaker and midbass.
Homemade crossovers
It happens that having become the owner of an expensive car acoustics, the owner discovers that the kit does not include crossovers. It is clear that it will be impossible to do without them, since the HF speakers can simply burn out.
What to do? The answer is ridiculously simple - make them yourself.
Tools
First, let's arm ourselves with the necessary tools:
- A good and convenient soldering iron.
- A special device that measures inductance.
- Glue "Moment".
- Ferric chloride.
- Foil fiberglass laminate.
- Heat shrink tube.
- Silicone sealant.
Step-by-step instruction
We begin the manufacturing process.
So:
- First of all, you need to carefully study the technical characteristics of the purchased speakers. It is recommended to pay special attention to the low frequencies of the tweeters, as well as the level of characteristic sensitivity of the LF and HF speakers.
- Then you need to select the correct electrical circuit, which involves connecting a crossover.
Note. According to experts, it is advisable to give preference to 2nd order filters, because in a cramped car interior there is a strong increase in the frequency response at medium-high frequencies.
- It must be remembered that high-frequency speakers, which are connected through a 1st order filter, strongly emphasize hiss, and low-frequency speakers over-emphasize bright sounds. As a result, when put together, you get a mess, in which there will be a lot of bright and hissing sound.
Note. At the same time, the wider the interior of the car, the more it will be possible to minimize these shortcomings.
Inductor
So:
- We wind the inductors for the speakers. Note that when doing this for a woofer, it is better to use copper wire with a diameter of 1 mm and insulated with a special varnish.
Advice. When making coils, it is recommended to use ferrite cores. This will make it possible to obtain smaller dimensions and weight, as well as reduce the consumption of expensive copper wire. In addition, it will also be possible to reduce the active resistance of the coil.
- It is recommended to monitor the resulting inductance using a unique measuring device.
Advice. When winding wire, it is highly advisable to make a turn and a turn, and then fix it with glue. This will make it possible to avoid problems that beginners often encounter.
Making a printed circuit board
So:
- It's time to draw the board on paper. This must be done based on the sizes of the resulting coils and resistors.
- We draw the board and transfer it to a sheet of special material.
Note. It would be a good idea to choose foil-coated fiberglass as such a material.
- We immediately drill holes for the electrodes of future parts and wires. Be sure to etch the board. This must be done as follows: place the semi-finished board in a ferric chloride solution.
Assembly
- We assemble the boards of our future crossover according to the installation diagram.
Note. We carefully glue the inductors and capacitors to the board. It is recommended to use a good glue such as Moment. Good fixation will allow the homemade separator to work flawlessly for a long time in conditions of vibration and shaking.
Connecting speaker wires
So:
- We connect the speaker wires using a regular soldering iron. When working, you need to be extremely careful and not confuse the outputs for the low-frequency and high-frequency speakers. You also need to pay attention to the polarity.
- Glue will come in handy here too. It is necessary to fill the wires that are soldered with “Moment”, which will again protect against vibrations and possible fractures.
Connection
So:
- We carry out a test connection and make sure that the signal is supplied to each speaker from the corresponding output of the homemade crossover.
- If necessary, you can also include a 4 ohm resistor in front of the RF filter.
Note. We remember that the sensitivity of tweeters is several decibels higher than the sensitivity of the speaker reproducing low frequencies - as a result, tweeters play louder than the woofer.
We wrap the crossover ready with our own hands with heat-shrink tubing, observing the required dimensions. Be sure to fill the edges with silicone to prevent moisture or dust from getting inside the crossover.
The presented instructions will help you make a homemade crossover for acoustics without any problems. During the operation, it is recommended to study additional photos and video materials.
As for the price of consumables, it depends on the number of coils and speaker outputs. The material that is used is also important.