|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
BOOKS AND ARTICLES
Leopard change his spots...
Headache car audio - interior resonance, manifested in the characteristic "buzz" on some bass notes. Frequency response measurements show at frequencies of 120 ... 160 Hz a "hump" ranging from 3 to 8 dB. To correct the "hump" most often use an equalizer, but this solution is not as simple as it seems at first glance. A professional high-quality device costs accordingly, and setting it up is not an easy task, requiring experience and measuring equipment. If you use a budget model, the sound quality is unlikely to improve. Two or three dozen general-purpose operational amplifiers are capable of leaving only memories from the sound. Therefore, the desire to do without an equalizer is understandable to everyone who works creatively on the installation. Let's admit the incredible - that all frequency response defects are defeated by the selected components and careful installation, and only an indestructible resonance remains. Even when using the highest quality components, this problem is not easy to solve. The first and most obvious way is to separate the crossover frequencies of the subwoofer and the rest of the acoustics. In this case, the subwoofer reproduces frequencies below 120 Hz, and the rest of the acoustics - above 180 Hz. These figures are approximate and depend on the size of the cabin and the features of a particular installation. Since crossovers of at least a second order are used in serious installations, the roll-offs of the frequency response are quite steep, and the band spacing is small. As a result, the subwoofer has to reproduce a wide frequency band and the problem of "rear" bass arises in all its glory. The tail was pulled out, the mane got stuck ... The way out was found where they were not looking for it, but you will have to start from afar - from circuitry. Budget series amplifiers, in order to keep up with their "big brothers" in terms of equipment, have long switched from a fixed cutoff frequency of the built-in crossover to smooth tuning. The only difference is that they save on variable resistors. To rebuild a second-order filter in a stereo version, you need a four-section variable resistor with good resistance matching, and in some cases also with different section resistances. A thing, if not custom-made, then at least not consumer goods. Therefore, they began to use the usual two-section ones, having accordingly reworked the filter scheme.
This is how filters of variable steepness entered the arena, in which only one of its links is rebuilt. Following budget amplifiers, such filters appeared in middle-class models. As an example, a fragment of the built-in crossover circuit of the Hifonics Mercury amplifier (Fig. 1). The scheme is simple - a passive high-pass filter of the first order, tunable over the range, and in addition to it - an active second-order filter, tuned to the extreme frequency of the range, that is, in total - a third-order filter. But unlike the classical version, when the cutoff frequency changes, the shape of the filter's frequency response also changes. At first glance - a drawback, a deviation from the canons. But if you approach dialectically - dignity is a continuation of shortcomings. Let's look at the frequency response (Fig. 2).
The graph in black shows the frequency response of the subwoofer channel with a cutoff frequency of 80 Hz and the frequency response of the HPF in the two extreme positions of the regulator. And in blue - the resulting frequency response in one of its intermediate positions. The result is obvious - in the region of interest to us, about 150 Hz, a dip of the required magnitude appeared. At the same time, the subwoofer frequency band remained within reasonable limits and there is no need to worry about the "rear" bass. And the wolves are full, and the sheep are safe. In addition, in the zone of operation of the first-order link, the phase-frequency characteristic is much more decent than that of a classic third-order filter. If you look at the test results of various publications, similar frequency response can be found in most modern crossovers and amplifiers in the lower and middle price categories. The conclusion is unambiguous even without opening - filters of variable slope are used in their design. Here is an example of how simplifying a design has improved its quality and expanded its scope. However, the possibilities of correction using this method are limited, so it is too early to talk about the extinction of equalizers. But setting up a whole equalizer for the sake of one "hump" is the same as shooting sparrows from a cannon. Instead of an equalizer, it is better to use a notch filter tuned to a frequency of 140 ... 160 Hz. The scheme of the simplest passive filter based on the inverted Wien bridge is shown in fig. 3. The quality factor of the filter is small, so fine tuning is not required.
The filter is connected between the line output of the source and the input of the amplifier. It is convenient to choose the capacitance of the capacitors equal to 0,1 μF, the resistance of the resistors is 10 ... 12 kOhm. When using small-sized parts, it can be placed in the RCA-"dad" case. This design has only one advantage - simplicity. There are many more disadvantages - the degree of correction in most cases is insufficient, and the characteristics depend on the output impedance of the source and the input impedance of the amplifier. To eliminate the shortcomings, the filter must be made active. The main condition that was set during the development of the circuit is the simplicity and high quality of the signal. Therefore, microcircuits were resolutely rejected - discrete elements are preferable in such conditions. The best amplifying element for a simple circuit is a field effect transistor. In addition to the high input impedance, the FET has a more linear response than the bipolar, the sound becomes warm and "tube". True, in simple circuits, a lack of field-effect transistors may appear - a large spread of parameters. However, this is easy to get around: it is enough to use transistors from the same batch in the design - within the package they look like twins.
The active filter circuit for one channel is shown in fig. 4. The first stage is a split load amplifier. Its task is to create anti-phase voltages to power the C2C3R4R5 filter unit. In the right switch position according to the diagram, this is the previously considered filter with attenuation of about 3 dB. In the left position of the switch, anti-phase voltages are supplied to the filter, and the attenuation at the tuning frequency increases to 5 ... 6 dB. The exact attenuation value depends on the characteristics of the transistor and the ratio of the resistances of the resistors R2 and R3. If you make them equal, the attenuation will be maximum (8 dB), but the output signal will be attenuated relative to the input by 3 ... 4 dB. The diagram shows the optimal variant of the denominations. The output stage is a conventional emitter follower. Its task is to eliminate the influence of the load on the characteristics of the filter. Capacitor C5 and diode VD1 - a power filter common to two channels. The filter is powered directly from the remote output of the head unit, since the current consumed through two channels does not exceed 10 mA. In addition to those indicated in the diagram, transistors KP303V (VT1), KT3102 with any letter (VT2) can be used. Diode VD1 can use any low-power silicon. Electrolytic capacitors must have an operating voltage of at least 16 V. The type of other parts is not critical, and, as they wrote half a century ago, "depends on the taste and capabilities of the radio amateur." The case must be metal, otherwise you will have to provide it inside with a copper foil shield and connect it to a common wire. Setting up a schema is easy. After checking the installation, you need to apply power to it and measure the constant voltage relative to the common wire at the emitter of the transistor VT2. It should be between 50 and 70% of the supply voltage and, if possible, be close in both channels. If this is not the case, you need to select the resistance of the resistor R3 within 1,2 ... 1,8 kOhm. The resistance of these resistors in both channels must be the same, this is a more important condition than the equality of constant voltages at the output. The input resistance of the filter is about 100 kOhm, the input voltage should not exceed 1,5 V - otherwise distortion may occur. If the voltage at the line output of the source is higher, a voltage divider will have to be added at the filter input (a 100 kΩ resistor in series with capacitor C1). In this case, signal losses will have to be compensated by adjusting the sensitivity of the amplifier. Since the input impedance is very high, it is better to install the filter near the signal source in order to avoid input interference. The output impedance of the filter is about 50 ohms, which is much less than that of most head units. This will eliminate the influence of the parameters of the connecting cable, so that the filter simultaneously performs the functions of a matching device.
The frequency response of the filter is shown in Fig.5. This is no longer just a filter, but a true "ambience equalizer". A device with this name and a very similar frequency response is used in top-end McIntosh amplifiers, but the circuitry is more complicated there ... Publication: www.bluesmobil.com/shikhman
▪ The development of surround sound systems - from mono to 3D ▪ About the visibility of distortion
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Samsung Gear VR Innovator Edition - virtual reality glasses for smartphones ▪ Protecting power grids from cyber attacks
▪ section of the site Personal transport: land, water, air. Article selection ▪ article And to live in a hurry, and to feel in a hurry. Popular expression
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page