1. Two-way (two-way frequency) and three-way (three-way frequency) speaker systems
The two-way speaker system has a simple structure and a relatively low cost. In order to solve the lack of this mid-range frequency, some manufacturers use a method of fading, that is, moving the frequency response characteristics of the woofer upward on the crossover network. The tweeter will wait for the frequency characteristic to move down. Another problem is that the crossover frequency can only be set between 500Hz-2kHz, and this area is an important part of the vocal and vocal spectrum. Therefore, people leave a sense of "emptiness" and distortion of hearing. Because of this, the requirements of the three-way speaker for the speaker unit are relatively high. If the performance of the unit is not good, the sound of the entire speaker system is not smooth enough, or there is severe phase distortion.
The characteristics of each unit of the three-way speaker system can be made without compromise, and their respective strengths can be fully utilized. The two crossover points can be selected at the upper and lower edges of the important parts of the midrange vocal and vocal spectrum, which has no effect on the sound quality. Therefore, the three-way speaker system reduces the distortion of the sound, improves the clarity of the sound, improves the performance of the cross-band between the low and high frequencies, and increases the power processing capacity of the speaker system, so it is a cultural performance, concert hall and opera house The best choice for sound reinforcement system.
2. Sensitivity and maximum sound pressure level (SPL max)
The speaker unit is a transducer between electric signal and sound, which requires it to be transferred to a very loud sound with relatively small input power, which requires the speaker to have a high sound pressure sensitivity, [sensitivity] In essence, it is a manifestation of [conversion efficiency]. Due to the differences in design techniques, materials and production processes used, the sensitivity of various types of systems can vary greatly.
Sensitivity refers to the electric power of 1 watt input to the speaker unit, and the sound pressure level measured at a distance of 1 meter away from the axis of the speaker. If the sensitivity of the two speakers differs by 3dB to achieve the same sound pressure level output, additional power is required. The input power is doubled, so speakers with higher sensitivity can produce a larger sound.
The input power capacity of the speaker system is generally much greater than 1 watt (generally between 100 watts and 2000 watts). Therefore, the maximum allowable electrical power can be input during actual use. To input the speaker at the rated maximum power, input the speaker in the axial direction of the speaker The sound pressure level generated at 1 meter is called the maximum sound pressure level SPL max example, sensitivity = 100dB, 1w / 1m speaker, if the maximum power withstand capacity is 1000W, then SPL max = 100dB + 30dB = 130dB, 1m.
3. Distortion and sound quality
The speaker factories have not stated the distortion rate of their products. In fact, it is a very important technical parameter. The sound quality is a relatively abstract evaluation. It is also impossible to state it on the file. It can only take a subjective listening comparison. Usually, Sensitivity and sound quality are contradictory. Manufacturers need to strike a proper balance between the two. Generally speaking, low- and medium-priced products are dominated by sensitivity, and the price-performance ratio is pursued. High-priced products emphasize sound quality and the highest. The level is both.
4. [Personality] and [Commonality]
Here, another relatively abstract and subjective performance evaluation is introduced. The sound used for sound reinforcement is different from the Hi-Fi audio equipment at home. It must be very compatible because each venue may perform different types of programs. , From operas to rock concerts, it may just be a speech report mainly based on language signals, so its sound system must be compatible with different program sources, to achieve [average] excellence, it can not focus on a certain purpose, and home The Hi-Fi audio equipment only needs to take care of the taste of a person or a small group of people. The [personality] of its products is allowed to exist, but as a professional sound reinforcement system equipment, this [personality] will become [limited Sex] or [defect].
Professional sound reinforcement equipment needs to serve a large group of the public, and the content of the program often changes. [Common] is a basic requirement. Compatibility is strong. Programs of different nature must have [average] performance. In addition, professional sound reinforcement equipment must It is "no rendering", "no exaggeration", and "loyal" to restore the sound source, which is [common] or [common].
5. Pointing characteristics of the speaker system
The sound emitted by the speaker is usually non-directional in the low frequency band (below 200Hz), and spreads evenly in all directions, but in the high frequency band, the sound transmission has a strong directivity. This directional characteristic (all types of speakers All are different) It is what we want to apply in the system design. The excellent constant directivity characteristics can concentrate the energy of the sound wave to the audience area during the site layout, avoiding the strong reflection surface of the sound wave and the sound field interfering with each other.
The directional characteristics of the speaker make the sound pressure level deviating from the axis gradually decrease with the increase of the deflection angle, and the sound pressure level attenuates by the square of the distance inversely with the increase of the sound wave propagation distance. If the two attenuations are properly selected, the two attenuations can compensate for each other, so that the sound field is more uniform. Large projects need to cover a relatively wide area, and a single speaker is usually not enough to cope with it. Multiple speakers need to be combined into a speaker group (display), and in the speaker system of the display, the constant directivity feature can prevent the sound waves of the middle and high frequency bands between the speakers from interfering between the speakers. The speaker is arranged in a figure eight shape, which can cover double of a single speaker, otherwise, the sound has interfered with each other in front of the speaker, which seriously affects the uniformity of the sound field and the clarity of the sound.
6. Power handling capacity of the speaker system
The power handling capability of the speaker (or the rated power of the speaker) is an important technical parameter. It represents the power input capability of the speaker to withstand long-term continuous safe operation. To understand the power handling capability of the speaker, you must first understand how the speaker driver is damaged. There are two damage modes of the drive:
One is the overheating damage of the voice coil (burning of the voice coil, overheating deformation, breakdown between the coils, etc.), and the other is the displacement of the diaphragm of the driver exceeds the limit value, making the tapered diaphragm of the speaker and / or the elastic components around it Damage usually occurs in low-frequency signals with many large amplitudes.
The sound signal is not a sine wave signal, but a random one. These random signals can be represented by three energy numbers. The effective value (RMS) is also known as the root mean square value. This kind of measurement result, close to the average value, basically represents the heating energy of the signal.
Peak (Peak) is the maximum level reached by the signal. For a sine wave, the peak level is 3dB greater than the effective value level. For a music signal, the peak level exceeds the effective value by up to 10-15dB. In evaluating a speaker The peak value is important in the displacement capacity of the system. The peak factor is used to explain the ratio of the peak level to the effective value level. For the pink noise source according to AES2-1984, the peak factor is 6dB, that is, the peak voltage is effective. 4 times the value of voltage.
The power processing capacity of the loudspeaker is the technical parameter measured under the condition that the permanent change of the electrical and mechanical properties is not more than 10% after the continuous operation of the pink noise signal processed by (AES2-11984) plus 2 hours.
7. The sound pressure level drops after loading (heating) (also called power compression)
The nominal power in all product manuals is determined by each manufacturer, which is the best value of the speaker under the test signal and conditions selected by the manufacturer. When the speaker enters the working state (for example, after 20 seconds or more at full power), After the voice coil and magnet are heated and heated, the original characteristics of the unit before heating are changed due to their performance degradation. At this time, the actual sound pressure output will be reduced. Conventional speakers, such as the voice coil temperature rise of 60 degrees -80 degrees, are common 3dB drop in the rated sound pressure level is the tolerance. If the voice coil has excellent heat dissipation and the temperature resistance is above 100 degrees, the actual sound pressure drop can reach 6 to 8dB. This is a quite amazing drop. As mentioned in the previous question, it doubles. The sound box only increases the sound pressure level by 3dB. If the sound pressure level of the sound box drops by 6dB, to compensate for such a big sound pressure level drop, the original sound box must be increased from four to four. Unfortunately, the audio industry has no such sound pressure level. To lower, the heat dissipation design of the speaker unit must be improved.
8. The impedance of the speaker unit
The impedance of the speaker unit includes, inductance, capacitance and resistance, the inductance and capacitance change with frequency, although the nominal impedance change in the speaker system is too large, it will affect the stability of the entire audio system, JBL latest The DCD dual coil differential drive design is to change the impedance to [pure resistance] without being affected by frequency changes, so that the entire audio system can work stably.
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