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Active three-way crossover. Serial crossover. Remember all. What criteria should you use to choose a car amplifier?

Speakers with a twist: the laconic design is combined with careful execution of the housing.

When developing and manufacturing a new acoustic model, the manufacturer tries to paint a portrait of its listener and evaluate the environment in which this system will be installed. But I want to describe the design, the ideologist of which was its future owner. Here is a short list of the wishes that we received as a guide to action from another customer. These should be floor-standing speaker systems for listening to calm music in a cozy home environment. They should be in harmony with the existing interior, but have a twist in the design.

The last, but categorical requirement was the use of the simplest first-order separation filters (it seems that the customer was greatly influenced by the many articles about the dangers of high-order filters).

The following picture emerged:

1) the low-frequency speaker will be made of paper - the order of the filter is mandatory, although an aluminum diffuser in combination with a light oak finish would perfectly meet the requirements of the apartment design;

2) acoustic design - bass reflex, since as a result of listening the client clearly preferred this type;

3) the system will be two-way;

4) the interior of the room implied the manufacture of a product with smooth lines, and here the unique “monolith” technique developed in our company for the production of cabinets came in handy. All its edges are rounded, which also has a beneficial effect on the problem of diffraction in the HF region.

And they didn’t forget about the highlight: the chiseled oak bass reflex tunnel, located on the front panel, perfectly complemented the smooth contours of the corners.

About the author

Boris Pukhov is a graduate of the Leningrad Polytechnic Institute, an acoustics specialist at the Peter Music company. He is directly involved in the development of custom-made speakers, not only for Hi-Fi systems, but also for home theater. The latest achievement is the launch of car subwoofers under the Bloodhound brand.

Having delved into history, we decided to take as a basis the development of fifteen years ago by the Norwegian company SEAS, since now in Russia there are no problems with such brands as VIFA, SCANSPEAK and SEAS. It was nice to note that the H333 eight-inch paper woofer and the H519 fabric dome tweeter are still in production today. The speakers were purchased and the process of bringing the client's idea to life began.

The body is made of high-density MDF (side and rear walls 19 mm, front - 25 mm). After cutting, the panels are glued around the perimeter with an oak block in such a way that labyrinths are formed at the joints - a 100% guarantee against leaks. The tightness of the structure is also evidenced by the fact that before veneering it is necessary to drill a technological hole, because Fluctuations in air temperature lead to retraction of the walls. In this way, two 39-liter cases were assembled.

Monolith joint: 1 - oak timber, 2 - MDF panel, 3 - veneer.

A feature of the “monolith” method is that the body is non-separable, and therefore, before installing the last panel, the Vizomat vibration-absorbing composition is hot rolled onto the internal planes and the filter is installed. The presence of internal struts gives the structure additional rigidity. What is characteristic is that not a single screw is used during assembly. A three-layer matte varnish coating reliably protects the case from fluctuations in humidity in the room and emphasizes the relief of the structure of natural wood. For installation on the support spikes, M8 countersunk nuts are installed in the bottom panel at the production stage.

A few words about the filter: inductors with an air core and interlayer impregnation of our own production. Metal film polypropylene capacitor K78-19, which has proven itself in acoustic filters.

Since these speakers do not require strong displacements of the low-frequency driver cone and there are no “winds” in the tunnel, we limited ourselves to a port with a diameter of 70 mm. The length was selected experimentally, tuning the body to the natural resonance frequency of the head (33 - 35 Hz). During setup, a plastic tunnel was installed, the length of which was selected experimentally and turned out to be 150 mm. Taking into account the rounded edges of the turned tunnel, we made it 160 mm long and glued it into the speaker body. The speakers were installed in the front wall on a specially milled mounting belt through a thin rubber gasket and secured with screws using self-unclosing bronze bushings.

The volume of the housing in the lower part was evenly filled with synthetic wool, the volume of which was selected according to the minimum resonant frequency of the system with the tunnel opening plugged. All experiments and settings were carried out on one case, and the second one was assembled in an image and likeness, because SEAS speakers are famous for their high stability of parameters of similar products. The client considered the listening result to be the main criterion for the quality of finished products. It was produced in conjunction with the conservative British amplifier Musical Fidelity A220. The soft timbre, lightness and delicacy of sound with good elaboration of the spatial image made it possible to listen to music for a long time without signs of fatigue, which suited their owner quite well. We nevertheless decided to measure the frequency response of sound pressure in the near field using the Audio Control SA-3055 spectrum analyzer using the built-in pink noise generator. The location of the microphone did not allow us to detect the operation of the bass reflex, as evidenced by the obvious blockage in the low-frequency region on the LED display (1 dB step), while during listening there were no problems with the bass. The sensitivity was found to be 89 dB.

In conclusion, I would like to note that the emotional perception of music greatly depends on the quality of the cabinet, and pleasing the eye is not the last task of modern speaker systems.

When installing a modern stereo system in a vehicle, the owner needs to choose the right crossover. This is not difficult to do if you first become familiar with what it is, what it is intended for, and as part of which speaker system it will work.

Purpose

A crossover is a special device in the structure of the speaker system, designed to prepare the required private range for each of the installed sound speakers. The latter are designed for operation within certain frequency ranges. If the frequency of the signal supplied to the speaker goes beyond the range, it can lead, at a minimum, to distortion of the reproduced sound, for example:

  1. if the frequency is applied too low, the sound picture will be distorted;
  2. when applying too high a frequency, the owner of a stereo system will face not only sound distortion, but also failure of the tweeter (high-frequency speaker). It may simply not withstand this operating mode.

Under normal conditions, the task of a tweeter is to reproduce only high-frequency sound, and low-frequency sound, respectively, low-frequency sound. The mid-frequency band is fed to the midwoofer - the speaker responsible for the sound of mid-frequencies.
Based on the above, in order to reproduce car audio with high quality, you need to select the appropriate frequency bands and feed them to specific speakers. To solve this problem, a crossover is used.

Crossover device

Structurally, the crossover includes a pair of frequency filters that operate as follows: for example, if the crossover frequency is set to 1000 Hz, one of the filters will highlight frequencies below this indicator. And the second is to process only the frequency band exceeding a given mark. Filters have their own names: low pass - for processing frequencies below a thousand hertz; high pass – for processing frequencies above a thousand hertz.

So, the principle by which a two-way crossover works was presented above. There are also three-way products on the market. The main difference, as the name implies, is the third filter, which processes the mid-frequency band, from six hundred to five thousand hertz.

Essentially, increasing the sound band filtering channels and then feeding them to the appropriate speakers leads to higher quality and natural sound reproduction inside the car.

Technical features

Most modern crossovers contain inductors and capacitors. Depending on the quantity and quality of manufacturing of these reactive elements, the cost of the finished product is determined.
Why are coils and capacitors included in a bandpass crossover? The reason is that these are the simplest reactive elements. They process different frequencies of the audio signal without much difficulty.

Capacitors can isolate and handle high frequencies, while coils are needed to regulate low frequencies. By using these properties wisely, the result can be the simplest frequency filter. There is no point in delving into the complex laws of physics and citing formulas as examples. Anyone who wants to become more familiar with the theoretical foundations can easily find information in textbooks or the Internet. It is enough for specialized specialists to refresh their memory about the operating principle of LC-CL type networks.

The number of reactive elements affects the crossover capacity. The number 1 denotes one element, 2 - respectively, two. Depending on the number and connection diagram of elements, the system filters inappropriate frequencies for a particular channel in different ways.

It makes sense to assume that the greater number of reactive elements used makes the filtration process better. The filtering circuit for unnecessary frequencies for a specific channel has its own characteristic called slope.

Filters have the inherent property of cutting off unnecessary frequencies gradually, rather than instantly.

It's called sensitivity. Depending on this indicator, products are divided into four categories:

  • first order models;
  • second order models;
  • third order models;
  • fourth order models.

Differences between active and passive crossovers

Let's start the comparison with a passive crossover. It is known from practice that the passive crossover is the most common and most often found type on the market. Based on the name, you can understand that passive ones do not require additional power. Accordingly, it is easier and faster for the vehicle owner to install the equipment in his car. But, unfortunately, speed does not always guarantee quality.

Due to the passive principle of the circuit, the system needs to take part of the energy from the filter to ensure its operation. In this case, reactive elements tend to change the phase shift. Of course, this is not the most serious drawback, but the owner will not be able to fine-tune the frequencies.

They are rarely found as separate equipment, but any car amplifier contains an active filter as an integral part. Due to the passive principle of the circuit, the system needs to take part of the energy from the filter to ensure its operation. In this case, reactive elements tend to change the phase shift. Of course, this is not the most serious drawback, but the owner will not be able to fine-tune the frequencies.

Active crossovers allow you to get rid of this disadvantage. The fact is that, although they are much more complicated than passive ones, the audio stream in them is filtered much better. Thanks to the presence of not only coils and capacitors, but also additional semiconductor elements, the developers were able to significantly reduce the size of the device.

They are rarely found as separate equipment, but any car amplifier contains an active filter as an integral part.

We also suggest that you familiarize yourself with the accompanying topic “”.

Settings Features

In order to get high-quality car audio as a result, you need to choose the right cutoff frequency. When using an active three-way crossover, two cutoff frequencies must be determined. The first point will mark the line between low and medium frequencies, the second - the line between medium and high. Before connecting a crossover, the car owner must always remember that it is necessary to correctly select the frequency characteristics of the speaker.

In no case should you apply frequencies to them at which they simply cannot operate normally. Otherwise, this will not only lead to deterioration in sound quality, but also to a reduction in service life.

Passive crossover connection diagram

Video: What is an audio crossover for?

We hope that this article helped you understand why a crossover is needed. Rate the article on a 5-point scale; if you have any comments, suggestions or you know something that is not indicated in this article, please let us know! Leave your comment below. This will help make the information on the site even more useful.

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.

Crossover(English) crossover or x-over, literally: 1) crossing, intersection; 2) signal spectrum separator).

Crossover in electronics - a separation filter (usually audio frequencies, for example, a filter for a multi-band acoustic system). Crossover is a class of special filters created specifically for use in various audio equipment, for example, Hi-Fi. Typically, dynamic heads (speakers, loudspeakers) used in audio systems are not capable of reproducing the entire spectrum of sound frequencies without distortion. Thus, a crossover allows you to divide the frequency spectrum into separate frequency ranges (bands), which can then be played by an appropriate speaker designed for this range (band) without distortion.

Another application of crossovers is multi-band signal processing, where each group can be processed separately using dynamic, effect and psychoacoustic processors (compression, limiting, de-essing, distortion, bass enhancement, exciting, noise reductions, echo, delaying, etc.)

In industrial designs of active crossovers, the most widely used filters are Butterworth, Bessel and Sallen-Key filters built on repeaters.
Bessel filters have the smoothest phase response (like a single RC circuit), but the total frequency response has a dip of 3 dB at the crossover frequency.
Butterworth filters provide a flat overall frequency response, but their phase response is steeper.
Finally, Sallen-Key filters (equal component filters) are very convenient for mass production because (as the name suggests) they require parts of the same rating and with a large tolerance, which is not the case with Butterworth and Bessel filters, which require precise parts
However, the phase and frequency characteristics of equal-component filters are the worst, so they are used only in budget models.
There are quite a lot of phase-linear active crossover circuits, such as those based on a Bessel low-pass filter and a Delianis phase corrector (Peter Lasky crossover).... and so on, but, as a rule, they are complex in calculations and settings, there are a lot of op-amps, precise resistors and capacitors.
The method of constructing separation filters using so-called complementary filters is largely free from the above disadvantages.... and the best characteristics have a separation filter on integrators, which, due to the peculiarities of its construction, is also a complementary filter and therefore has all its advantages. In addition, such a filter is characterized by high stability, low sensitivity of the filter parameters to the accuracy of the elements, very high identity of the characteristics of the low-frequency and high-frequency elements, a flat total frequency response and, finally, ease of calculation of the filter cutoff frequency and a small number of active and passive elements, and what is especially pleasing is - there are no coupling capacitors... in many cases it is possible to get rid of output coupling capacitors in the receiver and input capacitors in the amplifier up to the output stage of the PA, which further linearizes the overall phase-linearity of the overall audio path.

I really like one active separation filter circuit, which I have already made and installed several times in different cars.
Traces of a description of this filter can be found on the Internet:
http://www.digit-el.com/files/articles/crossover.pdf
After translation from English, it turned out that it was called a “constant level filter.”

But it sounds somehow wrong and I think it would be more correct to call this filter as "Active crossover filter with unchanged total frequency response."

Why I liked it so much - firstly, there are no coupling capacitors, and those capacitors that determine the coupling frequency are in the feedback loops of the op-amp and have a small capacitance. Selecting such a capacitor value, for example, from film ones, is not difficult.
The crossover frequency exactly corresponds to the nominal values ​​of the elements calculated according to the formula specified there.
You can take a resistor in the range of 24-47 kOhm as a basis and adjust the crossover frequency to the existing capacitances.
The schematic diagram of a two-channel active crossover filter with a bipolar power supply looks like this:


It is not as simple as it seems at first glance, if only because experience has shown that it requires speakers that can operate from a cutoff frequency lower/higher by 1.5-2 octaves (which is generally not a very big problem), it also requires the selection of a specific type of op-amp that will work in the adder and integrators.....
I’ll say right away that I’ve gotten the best result so far in terms of overall tonal balance and sound neutrality - this is a pair of LM4562 and AD8066, just as for a budget you can safely use both NE5532.
A little about the rest of the op-amps, what is imprinted in memory:
both AD823 - strong attenuation of signal energy in the LF/MF range
OPA2132, OPA2134, OPA2604, JRC4580, JRC2068 into the integrator - poor and sharp HF, some problems in the midrange.
two AD826 - maybe, but somehow too bright in the mid/high frequencies...
LT1469, LT1364, LM833 and many, many other options with the above op-amps are something in between, and probably everyone should choose what they like best in terms of sound with a specific amplifier and specific speakers.
You can hear the capacitors in the feedback circuits, the best ones that sound neutral are FT, Epkosy, K73-17 is not bad.... in any case, it is better to use film (not ceramic), at least Wima FKP2.
Overload capacity - more than two volts of the average input signal (with a power supply of +/- 12 volts) is better not to apply to such a filter - otherwise the first integrator will be included in the clip... well, that’s probably all the most important thing about this filter.

Below are just photos of the first filter option:





Photos of the second filter option (with adjustable channel output):




Active two-band filter of the fourth order.

We will talk about a two-band phase-coherent filter with Linkwitz-Riley approximation on the State Variable Filter, described here:

Functional connection diagram of the audio system:

Larger diagram:

A few explanations on the functional diagram of the audio system:
1. Toslink optical connections.

A digital signal comes out from the head and changer only when the device is activated.
That is, if the head is turned on, the number comes only from the head. If the changer is turned on, the number comes out only from the changer.
Next, the figure goes to the subwoofer DAC and through the Time Machine to the front DAC.
Thus, we need to turn a figure from two sources into two digital outputs.
The circuit for connecting and separating the optics is made on a Hex Inverter 74NC04 chip.
You can read about the Time Machine (time delay processor with S/PDIF interface) here:
http://sova-audio.blogspot.com/2012/07/2.html
There is already a new version of the Time Machine, which can be controlled remotely:
http://sova-audio.blogspot.com/2014/10/blog-post.html

In the Time Machine, the digital signal will be delayed relative to the sub and then the left edge will be delayed by the required amount relative to the right edge.

2. Volume controls.
Nikitin volume controls (RGN) Att7+ and Att7 developed by antecom:
http://forum.vegalab.ru/showthread.php?t=48665
I described the use of Nikitin volume controls in car audio here:
http://halin-caraudio.blogspot.com/2013/12/16.html
Since I made the MC420M amplifier have an input impedance of 20 kOhm, then accordingly I also matched the RGN to an input impedance of 20 kOhm.
2. The active filter itself is 4th order ( two-band phase-coherent filter with Linkwitz-Riley approximation on State Variable Filter) made at a crossover frequency of 3100 Hz.

This is what the assembled Block of Active Filters and Volume Controls looks like:

The volume controls are powered by a separate 5-volt stabilizer.
Interconnect cables used Canare GS-6 BLK and Canare L-2T2S BLK.
RCA connectors - Austrian, Amphenol.