Equalizer for car audio system
Car audio system - the construction is very complex and contradictory. Anyway, and closed the interior space of the vehicle with the matter arising resonances are not adapted for sound reproduction. The sound influenced by body shape, the materials used for the interior design, position determined by the manufacturers to the acoustics, and more on 's stuff. Of course, nobody argues that the creation of a good mobile audiocompress - idea absolutely hopeless. You can experiment with frequencies crossover, to find an acceptable location for the speakers to set the desired the levels on the amp. But even these efforts often fail to compensate for the existence of a component prepared automakers. And here comes to the aid of EQ.
Although in this respect there opinion. Many the installers from the large number of professionals are reluctant to go to in the introduction the additional signal path of the electronic device, as follow quite common in car audio purist philosophy "less is more". And in this they are, in General, right: less than components, the less reasons for entering the system noise and distortion. And feeling a right, they are willing to make great sacrifices, the day designing new jacks for optimum acoustics. In this the righteous, in fact, a fit they are carried with the client: to pay installation delights have all the same to him, and acoustics should be the corresponding, not 20 "conditional" per set.
On the other hand, is that the customer is to wait until the end of the creative flour installer, not wants. He needs for three days, within budget, and to play, "as he likes, but level." Here without introducing EQ already who rarely costs. This correcting device can be viewed from two positions. One is a means of rectifying the amplitude-frequency features a little blood. That is, even in non-ideal orientation acoustics and brand of mischief, from a musical point of view, saloon equalizer (EQ) can often provide quite a decent result. Otherwise speaking to approximate the sound of the car if not the ideal, although would, so to speak, the individual needs of the customer. In addition, solid professional instruments are often used for correction of the frequency response in preparation for competitions.
The equalizers are known, divided two types of graphic and parametric. Essentially both flavors are signal processors. The function of the device is to get from the head unit signal, and correct it send the amplifier. Both types of EQ differ mainly by the number adjustable bands of the frequency spectrum (typically from 20 Hz to 20 kHz), which the device can be only one and up to 30 or more. Each stripe in graphic and parametric equalizers stands out from the frequency the spectrum of the HF and LF filters, after which it starts with "correctional work": to adjust the signal level. Thus, correcting himself the device is a kind of set of band-pass crossovers (by the way, many equalizers simultaneously serve as electronic crossovers).
So they called for the visibility. Bodies management of many graphic equalizer made in the form of sliders, and plot of the desired frequency response curve can be observed directly on the front or top the panels. So using them is usually not too difficult, especially those that are used for operational adjustments. Graphic EQ have fixed adjustable bands, and Central frequency in them does not change. These devices differ in the width of the bands: one half and one third of an octave. There are those who have part of the bands distributed in breadth one octave, and the remaining one-half octave or one one third. It is clear that the more bars, the better the adjustment. Frequencies above and below the center frequency adjustable stripes define its width or the figure of merit. The more we expose the signal level at adjustable band, so it already, the "skalistoe" frequency response will be. And Vice versa: at a lower level addresses a wider range of frequency bands, causing more flat response. There are, however, the device bandwidth (q-factor) which does not depend on the rise frequency characteristics (the so-called "Constant Q"). When you configure graphic equalizer "problem" frequency must match (or be close) with a center frequency of the band to perform proper correction.
Again the name of this type EQ speaks for itself. In the parametric EQ can be adjusted three parameters: center frequency, width, adjustable bands and, of course, increased. What makes these devices more flexible in compared with the above graphic devices, although adjustable bands they have an order of magnitude less, and the entire frequency range they rarely overlap. But in the "coverage area" parametric the equalizer can achieve dramatic results in the fight against resonances. The user personally, however, within certain limits, can set the center frequency. Band width in parametrica depends from the quality factor (Q) and is set depending on the magnitude of the problem plot of the frequency spectrum. The higher the q, the narrower the strip, and on the contrary.
Yet, as we have said, should to distinguish between the equalizers for operational adjustments and those that used for one-time settings. The first all clear. In the last time mass producers have a knack for churning out devices poludniowy for installations directly into the dashboard or somewhere else nearby. It really convenient: the equalizer is right at hand, and the number bands (5-10) is enough that the listener could at any time to adjust the tone according to his own, turning (podvigov) pair adjustments. Simply put, everything is done by ear, without any measuring equipment.
Different devices for disposable settings frequency response. Not really, of course, disposable (if you prefer, you can to beat), but, as a rule, the parameters are set for a long time. This process is quite time consuming, and without the aid of special equipment is necessary here. The minimum that is required, is a real time spectrum analyzer (RTA) with source pink noise test signal with extremely uniform the distribution of energy in octave bands. The hearing resembles a static interference in the radio).
Still need a hefty supply patience, since the presence of the measuring complex no result guarantees. For example, when playing pink noise we put the microphone in the region, usually the head of a listener, and we'll schedule The frequency response. Then move the MIC for twenty centimeters to the left. And what do we see? And the fact that in a confined cabin space frequency response curve is quite changed compared to the original. The reason is that direct and reflected sound in the cabin is summarized, and the amplitude-frequency the characteristic is very sensitive to any misalignment of the microphone. So align the equalizer frequency only by the results of one measurement, filmed with a single point. How is it possible?
One way is the calculation of so called "spatial average" graph is the frequency response obtained with six to eight positions in the cabin. That is, the averaged curve, taken with 6-8 "strategically important" areas of the cabin. But, first, business is pretty dreary, and secondly, be aware of the fact that the human ear has the ability to separate the direct sound waves orientation of the reflected from the cladding and glass. Real time the analyzer mixes all in one pile, while optimal from the point of view of subjective perception, is a plane curve, which is somewhere in the middle frequency response signal acting on our ears directly from the speakers and the frequency response of the reflected sound. To find a middle ground can try using the method disclosed famous American specialist in car audio mark Ramrakha. And he warns that this method of correcting the frequency response is not addressed to the participants car audio competitions "on the flat curve", and is designed, say so, for optimum sound reproduction and accordingly listening (that perfectly smooth frequency response and optimal sound is two big differences, we wrote in the last issue).
Now, mark recommends to start to set to zero the knobs bass and treble on the head unit, the equalizer is in a Central position, and fader and knob volume at normal listening position. Then pink noise from the outputs of RTA is applied to the inputs of the equalizer.
When adjusting medium and mid bass frequency balance knob should be turned to the left, so we heard only the left speakers. The microphone in this case is directly in front of the left loudspeaker at a distance of 20-30 weather and directed strictly at its center. In this case, the microphone captures only the direct sound wave and almost deaf mirrored. After that can move (rotate) the equalizer knobs (those that are responsible for bands from 150 Hz to 1.5 kHz) in search of a plane curve The frequency response. It is recommended not to deviate from the Central (as a rule, fixed) the provisions of engines or whirlings".
When working with bass microphone is placed in the place where the head is usually the "main" listener - driver. The microphone must be directed upwards. Regulated bands from 45 to 150 Hz. The other, below 45 Hz, it is better not to touch, and to leave in a fixed (Central) position. Few speakers can reproduce these UltraBase frequency, so that the increase of the signal level on these bands you can only overload the amplifier and get a portion distortion deep bass passages. At frequencies from 40 to 100 Hz level should to raise approximately 5 decibels to prevent the masking effect road noise (reducing the sensitivity of the auditory organs in response to road noise), which particularly affects the perception of the lower the bass.
It remains to medium-high and correct high-frequency components - bands from 1.5 kHz and above. The microphone again set in the area of the headrest of the driver's seat, being facing left front speakers. After correcting frequency response the microphone is shifted by 3-0-35 centimeters to the right, made adjustment to obtain the averaged frequency response curve. For reliability, you can try several of the provisions of the microphone: high frequencies are known, usually require fine tuning.
But the measurements the measurements, and to hear all still have ears. In other words, whatever the objective reality, a little bit of subjectivity here wouldn't hurt. Therefore, the final chord equalizer settings, requires the involvement process hearing bodies and test drives. You can even not a test, and those that listening to the client, but it is very desirable that the musical material overlaps the entire frequency spectrum. Preference to normal, live instruments (piano, saxophone, drums, etc.) before synthesizers is also evident. Particular attention should be paid to "suspicious" settings. For example, if the frequencies above 150 Hz, the gain of the signal in the adjacent bands exceeds 6 dB, try lowering the level by 3 dB and listen again the test composition. If the second option sounds more convincingly then you can safely trust your musical perception reality.
Author: G. Samoilov, 12 Volts; Publication: www.12voltsmagazine.com, www.cxem.net