Damage analysis of high pitch unit for professional speakers

First. Reasonable distribution of loudspeaker and power amplifier

In the field of professional sound reinforcement, the equipment of sound equipment is very particular, during which the power amplifier and speaker is the most important, power amplifier and speaker equipment touched many aspects, such as power amplifier trademark, power tube type selection and low sensitivity speaker should be equipped with what kind of power amplifier. We all know that after the auditorium acoustic planning, the speaker power needs to be determined according to a series of accounting, and then the amplifier power is determined by the speaker power. But how to choose the best match between the two power?

An inexperienced tuner may assume that the output power of a power amplifier is too high to cause damage to the tweeter, but that's not the case. In professional occasions, loudspeakers can generally withstand three times the rated power of the large signal impact, instantaneous withstand five times the rated power of the peak impact without damage. Therefore, under normal circumstances, the speaker rated power takes 1/2 of the power amplifier, and there will be no problem. Thus, it is rare to assume that the high-pitch unit is burned by a power amplifier rather than by an accidental shock or long-time whistling of the microphone. It is well known that most speakers have multiple speaker units, and each speaker unit receives different power distribution according to the different frequency points. Fig. 1 is a diagram of the dynamic and static energy distribution in nature. In general, the percentage of power distribution of each speaker unit is shown in Fig. 1. In the figure, the frequency band assigned by a loudspeaker is read out from abscissa coordinates, and the percentage difference of the corresponding ordinate is the assigned power. For example, a two-way speaker with a frequency division point of 1.6 kHz (point A in the figure), a tweeter withstands 100% - 78% = 22%, and a bass unit withstands 78% - 0% = 78%.

The rated power of loudspeakers is usually marked by professional loudspeakers with maximum pink noise power, while the symbols of fever and civil loudspeakers are confused, but the base is the total power of each unit. That is to say, the rated power of the loudspeaker refers to the analog signal power that the pink noise or the broadband can withstand. Fig. 1 shows a 1.6 kHz divider with a rated power of 100 W. At rated power, the bass unit can allocate the output power of 78 W, while the tweeter only allocates 22 W. Therefore, the speaker can withstand the application of 100 W pink noise power or general program signal power, but with 100 W single-frequency signal to test, regardless of the tweeter and bass unit may be damaged. For example, if a three-tone speaker has a dividing point of 4 kHz, then the endurance power of the tweeter is only 5% of the nominal power. Assuming that the power distribution is improper, the damage to the tweeter unit will be simplified.

We know that in the 20 Hz to 20 kHz range of the human ear, a lot of energy gathered in the music signal is generally in the middle and low frequency band, and the high frequency band energy is only equivalent to 1/10 of the energy in the middle and low frequency band. In general, there are not many high-pitched components in human voice and music signals, but more high-pitched components in metal instruments and string music. Therefore, the power lost by the high-pitched speakers is much lower than that by the low-pitched speakers in order to balance the high-pitched and low-pitched sounds. Given a speaker to announce different sizes of motions and motions, under certain impedance conditions, if the nominal power of 200 W amplifier to 400 W or several times the output is actually very simple, but the distortion of the amplifier (THD) will greatly increase, this distortion first occurs in the medium and low frequency signal of high frequency harmonics, the greater the distortion, high frequency. The greater the harmonic energy, and these high-frequency distorted signals will enter the treble head with the high-frequency music signal, what will happen? The power distribution ratio of the general speakers is based on the rules shown in the drawings.

For a three-frequency speaker, under normal conditions, if the input signal to the speaker doubles, the power of the tweeter will only increase by 5W; but assuming the power amplifier is lacking, the signal overload will be reduced, and the high-order harmonic component will increase sharply. In addition to the original 1 kHz sine wave, there will be many odd harmonics, such as 3 kHz, 5 kHz sine wave energy, resulting in a significant increase in the proportion of high-pitch components in the signal, which will constitute a signal in the high-pitch spectrum energy far beyond the high-pitch unit can bear the power. Even if the total signal power has not reached the rated power of the speaker, the tweeter is now overloaded and damaged. This situation is shorter than signal overload, but no risk of cutting. When the signal is not distorted, short-term overload of 1 kHz signal, power energy falls on the loudspeaker unit with larger power, does not need to exceed the short-term maximum power of the loudspeaker, and generally does not constitute an error in loudspeaker power distribution and damage the loudspeaker unit. Therefore, in normal operation, under certain impedance conditions, the power amplifier should be greater than the speaker power, but not too large. In general use, the undistorted rate of the amplifier should be 1.2-1.5 times of the rated power of the speaker, and 1.5-2 times in large dynamic situations. This ensures that the power amplifier does not constitute distortion when the loudspeaker is at its maximum power.

Second, rational use of divider.

In a loudspeaker system, the frequency dividing circuit plays an important role in restoring the electroacoustic signal of the loudspeaker system. Especially in the middle and high frequency parts, the effect of the frequency division circuit is more obvious. The effects are as follows:

1. reasonably cut out the operation frequency bands of each unit.

2. reasonably allocate power for each unit.

3. Make the units have proper phase connection to reduce the sound dryness and distortion.

4. use the characteristics of the frequency division circuit to compensate the sound defects of the unit in a certain frequency band.

5., smooth and smooth the frequency bands.

However, if the input frequency division point is not used properly, or the loudspeaker operating frequency planning is unreasonable, it is likely to cause damage to the tenor unit. Therefore, when using the frequency divider, it is necessary to select the frequency divider according to the operating frequency plan of the loudspeaker supplied by the manufacturer. On the assumption that the frequency division point of the tweeter is low and the power burden is too heavy, the tweeter is simply burned down, as is the case with the mezzo horn.

Third. Correct the equalizer correctly.

The correct adjustment of the equalizer is also crucial. Frequency equalizer is designed to compensate for the various defects of indoor sound field and the frequency inhomogeneity of loudspeakers. It should be debugged by practical spectrum analyzer or other instruments in operation. The transmission frequency characteristics after debugging should be relatively smooth in a certain plan. But many times, some tuners who do not have sound common sense arbitrarily debug, and even a considerable number of people, the high-frequency and low-frequency parts of the equalizer too high, in the equalizer panel form the "V" shape. Assuming that these frequencies are forward more than 10 dB compared to the mid-tone frequency (the equalizer's scheduled amount is generally (+12 dB), the electrical power of the equalizer is more than three times higher than that of the mid-tone part. In this case, not only the phase distortion of the equalizer must be seriously stained to the music sound, but also the tenor unit of the loudspeaker can be easily burned down, which is also the primary reason for burning the loudspeaker. Of course, the sound system planning should be based on practice, such as the size of the site, use, acoustic conditions, such as inductive consideration, according to the practice of the use of conditions to determine the maximum continuous sound pressure level, and then determine the maximum SPL value of speakers.

Four, pay attention to the volume of the scheduling.

Many users put the attenuator of the back amplifier in - 6dB, - 10dB, that is, 70% - 80% of the volume knob, or even half of the direction, but by increasing the input of the mixer to reach the appropriate volume, the user thought that only the power amplifier left margin, the speaker is safe, in practice this is also a mistake. The attenuation knob of the power amplifier attenuates the input signal. If the input of the power amplifier is attenuated - 6dB, it means that to maintain the same volume, the mixer or the front stage must output 6dB more, and the voltage must be doubled. The dynamic margin of the input signal, commonly known as "overhead space", will be cut in half. At this time, if there is a sudden big signal, the output of the mixer will be overloaded and the clipping waveform will appear. Although the amplifier is not overloaded, but the input is amplitude waveform, high-pitch component is too heavy, not only high-pitch distortion, high-pitch unit may also burn out.

Of course, in some occasions, especially about the square play, we can also install high-pitch protectors, traditional high-pitch protectors are only installed on the unit with thermal resistors, insurance resistors, and some even series of small lamp beads and other backward technical means, the protection effect is poor. The new generation of professional loudspeaker high-pitch unit protector uses no-original circuit skills, can effectively deal with the high-pitch unit burnout caused by surge, harmonics, high-frequency circuit series into low-frequency, excessive current, high voltage, instantaneous switch and other reasons, does not affect the high-pitch effect, does not load the power amplifier, will not appear high-pitch Gaco. It is a phenomenon. For these elements, the protection effect can reach 91%.

Through the above analysis, we can clearly understand: speaker firing tweeter is an important reason for the power amplifier is too small, not too large. The signal sent by the power amplifier is itself cut signal, causing damage to speakers. Therefore, when equipped with sound, we must establish a correct understanding, to use the "big horse trolley" plan, to prevent the power amplifier from sending out the clipping signal and damage the high-pitch and medium-pitch speaker unit. In the planning of the sound system, the power amplifier and the loudspeaker should be matched according to the above principles. In practice, the equipment in each link should be used reasonably, so that the equipment can be protected and the sound system can achieve the best results.