Reason for the tweeter of professional speaker burned

Times:200次 Date:2012-02-03

Writer-Andy  Source-Professionadl Audio Website

The midrange、tweeter of the speaker burned are common in many professional occasions, such as the studio, theater, conference room, hall, etc.


A. Rationally allocate the speaker and the amplifier


The inexperienced tuner thinks that the output of the amplifier is too large, leading to the damage of the tweeter, actually otherwise. In the professional situation, the speaker can generally bear 3 times as many as the large signal impact at rated power, and in instantaneously can withstand 5 times as many as the impact in the peak at rated power without damage. So if the rated power of speaker is half of that of the amplifier, it is not a problem. Therefore, not by accident strong impact or microphone screaming for a long time, but by the power amplifier power is so large leading to the tweeter burned is less common.


As we all know, there are many speakers in one speaker box. The power each speaker born is distributed according to the difference of the crossover frequency. For example, the crossover frequency for one two way speaker is 1.6 kHz, the power for the tweeter is 100%- 78% = 22%; for the woofer is 78%-0% = 78%.


The general professional speaker box will mark the maximum pink noise power, audiophile and civilian speaker boxes mark a vague, but all of them are the total power of the units.

That is, the rated power of the speaker is the power of the analog signals which the pink noise or wideband can withstand. One two way speaker with1.6 kHz crossover frequency, 100 W rated power, at rated power, woofer can be assigned to 78W output power, and tweeter only assigned to 22W. So if input 100W of pink noise power or ordinary program signal power to the speaker, it is no problem. But if test the speaker with 100W monophonic signal, either the tweeter or the woofer may be damaged.


If the crossover frequencies of the midrange and tweeter are 4kHz, then, the tweeter can only withstand 5% of the marked power. It is easy to damage the tweeter with the misdistribution of the power.


We know that there is not so much treble in human voices or music signal, while relatively more in metal instrument and stringed music, but the power distribution proportion of the speaker basically conforms to the rule of the attached figure. Take three-way speaker as a sample, in normal circumstances, if the input signal increase 1 times, the power of the tweeter increases only 5W; but if the power of the amplifier is shortage, leading to the reduction of the signal overload, then the higher harmonic component will increase. Originally 1kHz sine wave, produce large quantity of odd harmonic, such as 3 kHz, 5 kHz sine wave energy, which increase the proportion of treble greatly, causing the treble energy spectrum of the signal far more than the power that the tweeter can withstand. Even though at this time, the total power is not up to the rated power of the speaker, the tweeter has been overloaded and damaged. This is more dangerous than the short-term signal overload while without reduction. If the signal is not distorted, short-term overload 1 kHz, the power energy will fell on the woofer which is with larger power, then it may not over the short-term maximum power of the speaker, and generally won't cause the misdistribution of the power, which will lead to the damage of the tweeter. Therefore, normally, the rated output of the amplifier is 2 or 3 times than that of the speaker, to guarantee that in the maximum power of the speaker, the amplifier will not distort.


B. Misuse of frequency divider


Misuse of crossover frequency, or working frequency range of the speaker is unreasonable may be the reasons of damage of a tweeter. In the use of frequency divider, should choose the crossover frequency rationally according to the working frequency range which offered by the manufacturer.   For the crossover frequency of tweeter, if you choose a low one, the tweeter that withstand will be overload, and easy to burn the tweeter. Same as the midrange median.


C. Improper of equalizer


The adjustment of the equalizer is important. Frequency equalizer is designed to compensate all kinds of indoor sound defects and nonuniformity of each frequency of speaker.

We should use the actual spectrum analyzer or other instrument to debug the equalizer.

After debugging, the transmission frequency characteristics should be relatively smooth in a certain range. Many unqualified mixer debug the equalizer arbitrarily, and even adjust the high frequency and low frequency to too high to form a “V” shape. If the frequency is adjusted more than 10 dB (equalizer regulation variable generally is ± 12 dB), the power is 3 times than the midrange. This situation, not only the phase distortion of the equalizer will stain the music, but also the tweeter extremely easily gets burned. That is the main cause for the tweeter burned.

Of course, the sound system should be designed according to actual condition, such as field size, use, sound conditions, etc. We should determine the maximum continuous SPL (sound pressure level) according to the actual conditions, then to determine the maximum value of SPL.


D. The adjustment of volume


It is wrong for many users adjust the attenuator of the power amplifier at 6 dB, in- 10 dB, that is 70% to 80% of the volume knob, or even half of the position, to achieve appropriate volume by increasing mixer input, thinking that the speaker is safe for there is surplus for power amplifier. The attenuation knob of a power amplifier decays the input signal. If the input attenuates -6 dB, it means that, mixer or pre-stage must output another 6dB to keep the same volume, and the voltage is 1 times higher, the dynamic surplus commonly known as "head space” will be cut in half. At this moment, if there is a sudden large signal is input, the mixer will be output overload, and appear drop waveform. Although the power amplifier is not overloaded, the input is drop waveform, and the treble component is overweight, leading to the distortion of treble, and also burn out of the tweeter.


Based on the above analysis, we can make it clear that one important reason for the tweeter burned, is the power of the amplifier is too low, but not too large. The output signal from the power amplifier is reduced signal leading to the damage of the speaker. So, when configure the speaker, remember to use "a big horse to pull a small cart" concept, to prevent reduced signal output from amplifier and damage midrange and tweeter. When design the sound system, design the power of the amplifier and speakers according to the above principles. Then in actual operation, all links of equipments use reasonably can protect equipments, and achieve the best effect of sound.