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BOOKS AND ARTICLES
New profession "Ilyich's Lamp"
The idea of using an incandescent lamp in a high-frequency radiator circuit in a multi-band automotive system appeared after a long struggle with the suppression of the sensitivity of the RF heads by other available methods. All of them were based on the use of resistances. The first RF crossover circuit looked classic (Fig. 1):
After listening to music for a short time, I came to the conclusion that at an increased volume level, the HF sound pressure level prevailed over the rest of the frequencies to such an extent that discomfort arose. I had to either use the tone controls, or just turn off the music. By my nature, I didn’t want either one or the other, so I joined the struggle for a “comfortable” sound. First of all, a resistance appeared in the crossover, connected in series with the speaker (Fig. 2). The capacitor had to be re-selected because the load resistance changed and the cutoff frequency along with it. The sound pressure has been reduced. But "comfort" was not achieved. There was an opposite effect. At higher volume levels, the HF components were in moderation, but with a decrease in volume, the hand itself reached for the tone controls. I had to try another option for regulating sound pressure - shunting the head with a resistance of 10-30 ohms (Fig. 3). This method is sometimes used. The smaller the value of the shunt resistance, the greater the suppression. But the picture turned out somewhat different than it was intended. Basically, the resonant "hump" is suppressed, and the overall level change is negligible. The impact on the frequency response is also not bad, but the main task has not been solved. Nothing worked without tone controls. Series and parallel resistors or circuits in this case are called dissipators. (dissipate means to scatter). They not only dissipate power, but also absorb the products of intermodulation distortion in the dynamics. So their influence on the character of the sound should be especially noticeable in inexpensive tweeters (Ed.) Tone control at its core is an increase or decrease in sound pressure in a certain frequency band, depending on the specific model of the head unit. Everyone has different adjustment options: on some devices they would be enough, on others they are not. There is also an opinion that the use of built-in tone controls worsens the sound of the system due to the correction of the frequency response of the head unit and additional phase distortions. In addition, there are restrictions on the acoustic installation scheme used. When using a two-band front, when the adjustment band almost completely coincides with the tweeter's operating area, adjusting the sound pressure with the tone control is not so critical. But in systems with three bands, such an adjustment cannot give the desired effect, since when it is used, the frequency response of the midrange head will be distorted, part of the working band of which necessarily falls into the treble tone control zone. As a way out, in these cases, the use of an equalizer with a sufficient number of control bands is justified. Using a simple 7-9 band EQ may not produce the desired effect. More advanced equalizers already cost a lot of money, which dramatically, one might even say - completely excludes their use in most amateur installations. Although, if we consider the system as a whole, the use of a multi-band equalizer will reduce the time when fully tuning the entire system. But that's not what we're talking about right now.
An idea arose - to use incandescent lamps to limit the level of high-frequency components at high volume. When heated, the resistance of the coil will increase and the power will be limited. Barretters are sometimes used in crossovers to protect against overload - the same lamps, but filled with hydrogen. Hydrogen contributes to the rapid recovery of the low resistance of the filament. In this case, due to a sharp change in resistance, the dynamics of high-frequency reproduction will be disrupted. If you use a conventional lamp - there will be a smooth compression of the high-frequency range. The filament has a thermal inertia that depends on its mass. The more powerful the lamp, the greater the thermal inertia. The use of a light bulb as a dissipator was initially simulated on a computer using the MicroCap program. The crossover circuit took the following form (Fig. 4):
Circuit with series resistance. The same circuit was used to simulate the operation of a crossover with a light bulb.
A crossover circuit was simulated, the head was replaced with an equivalent circuit (to account for the effect of the inductance of the head itself). Then the frequency response graphs were obtained for all the options considered above. The results of modeling the frequency response are shown in the graph (Fig. 8): At low volume, the resistance of the light bulb is about 0,5 Ohm. The frequency response of the crossover in this section is almost the same as the frequency response of the crossover without resistance. From the frequency response graphs it can be seen that the decrease in pressure by -3 dB for all curves occurs at approximately the same frequency. For the option with a shunt resistance, the value of the capacitor was changed, since the cutoff frequency at the considered value went up.
After the "theoretical part" I moved on to practice. It was necessary to measure the resistance of the lamps at different voltages. By setting a different current with a rheostat, he measured the voltage on the lamp, the current strength and calculated the resistance according to Ohm's law. For three types of lamps, the following results were obtained (Fig. 9-11):
The graphs show the voltage value at which a weak heating of the center of the spiral begins. The results After making changes to the scheme of his crossover, he began to listen. Let me remind you that the "comfort" of the sound was determined by ear. The use of the RTA analyzer was not supposed to be carried out due to the lack of it even on a citywide scale. Only by ear. If during prolonged listening there is no desire to use the tone controls, or turn off the source of "irritation", then I believe that the goal has been achieved. In my system, the installation of bulbs from the interior lights, it seems to me, gave the expected effect. The "whistling" effect is gone, and there is no need to use the tone controls to increase or decrease the volume. Publication: www.bluesmobil.com/shikhman
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Comments on the article: Ghosh For more than 5 years I have been using acoustics with light bulbs in the HF link. The result is satisfying. I rarely use treble tone controls, it depends on the format of the file being played.
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