When we get the color page of a speaker, we assume that the technical indicators are all true and reliable. As long as we measure these indicators comprehensively, we can know the grade, price and applicable occasion of this speaker. This is the speaker technology. The importance of the indicator. Let's discuss it below!
Power handling
The so-called speaker power refers to the electric power that the power amplifier feeds to the speaker unit. It has two indicators, one is rated power and the other is maximum power.
The rated power of a speaker refers to the speaker (speaker) inside the speaker, which is fed with a long-term pink noise signal within a certain frequency range without permanently damaging the electrical signal power RMS. This is the speaker power normally labeled. The maximum power is that the speaker (speaker) is fed with a pink noise signal in the rated frequency range, and the speaker is subjected to power for 1 second interval for 2 s, repeated 10 times without permanent damage.
So what is the relationship between rated power and maximum power? In practice, we generally think that the maximum power is 2-4 times the rated power. Therefore, the power (effective value) of the electrical signal we usually feed to the speaker is within 3 times of the rated power, which is safe for the speaker.
As for the power of the speaker, we can use the sound field design to calculate, or use the empirical data to select, generally choose the power of the speaker in the 5 watt / cubic meter hall volume. Half of the use of language sound reinforcement.
Impedance and Impedance Curve The impedance of the speaker is the ratio of the voltage at the input of the horn coil to the current through the voice coil. And this applied voltage must be varied (AC). The ratio of voltage to current (impedance) exhibited by alternating current at different frequencies varies. Technically, we define the minimum impedance that occurs after the maximum impedance at the resonant frequency of the low-frequency part of the impedance curve is the impedance of the horn. The resistance we usually measure with a multimeter is the DC resistance of the speaker voice coil, which is about 80% of its nominal impedance value.
The impedance value of the speaker (speaker) is actually a load impedance for the power amplifier, and the output impedance of the power amplifier is small, which can be regarded as a constant voltage source. When the load impedance is smaller, the output power is larger (but attention should be paid to the safety of the power amplifier tube of the power amplifier). At this time, the current flowing through the voice coil of the speaker is also larger, and the line loss of the speaker line is also larger. The general impedance of 8 ohms is the ratio of the signal voltage to the current at the input of the speaker. It is actually the impedance of the speaker woofer (equivalent parallel connection). This is a compromise between considering various factors, not the bigger the better, the smaller the better.
Frequency Response Frequency Response
The frequency response of a speaker is fed to its pink noise signal (power is 10% of rated power). The sound pressure level of the speaker changes with frequency when the value is stable and the distance is a certain distance on the reference axis. The corresponding change relationship is represented by a curve, which is the frequency response curve. The indicator given by the general speaker is the average value of the frequency response curve, and the value of the corresponding low-end frequency and high-end frequency when the 3db is decreased. Of course, the ideal is 20hz-20khz containing the entire audible audio.
But in reality it is impossible and it is not necessary. For the impossible aspect, we can use a combination of high, medium and low frequency speakers with their own frequency characteristics, which can be close to the range of 20hz-20khz. If it is not necessary, it can be understood as different applications, different requirements, can be satisfied. For example, as a pure conference sound reinforcement, we do not need to use the frequency response between 20hz-20khz, but only need to reach 100hz-12khz, the frequency response will increase the noise. )
Sensitivity Axial Sensitivity
Speaker sensitivity is an indicator of the efficiency of speaker electrical acoustic conversion. It is defined as the pink noise signal fed with 1W power, the sound pressure value measured at 1m from the unit on its axis.
Do not underestimate this indicator, it plays a decisive role in the rational selection of power amplifiers and the reduction of system cost.
For example, the sensitivity of one speaker is 95db, and the sensitivity of another speaker is 98db. For example, a power amplifier with a power output of 400w is used to drive the first speaker to produce a sound pressure value of 115db at a certain point. With the second speaker, we only need a full power of 200w output power to push the same sound pressure level. The cost of the amplifier is directly related to the magnitude of the output power.
The directivity of a directional loudspeaker is a characteristic of the relationship of sound pressure as a function of the direction of the acoustic radiation axis. A cluster of curves is used to represent a directional graph. Generally expressed in the horizontal and vertical radiation angles. The definition is that the horizontal coverage angle when the sound pressure level of the speaker is decreased by 6db is the horizontal radiation angle α, and the vertical coverage angle is the vertical radiation angle β when the sound pressure level of the speaker is decreased by 6db.
The directionality of a speaker is determined by the horn directivity of its tweeter. Since the radiation angle in the vertical direction is smaller than the horizontal direction, we can design an effective sound field coverage according to actual needs. It is necessary to use sound speakers with different directivity. If it can't be covered, it can be compensated by stacking the speakers. Linear array speakers can also be used to meet the requirements.
Crossover and multi-cell parallelism is impossible because of the good frequency response of a speaker over the entire audio range. It is also necessary to have a speaker rated power that is very large and unrealistic and impossible to achieve. Therefore, in an actual speaker, a plurality of speaker units generally work together to approximate the entire audio range. To achieve high-power output speakers, we can use multiple units of speakers in parallel to work. Therefore, in the speaker technical indicators, the specifications of the two-way, three-way, four-way and their respective crossover points are indicated.
In use, power division and electronic frequency division can be selected to meet the requirements. Similarly, in order to achieve a large sound pressure output, two or more woofer units can be used in parallel to increase the rated power to meet various needs.
Maximum sound pressure level The maximum sound pressure level of a speaker is the sound pressure level obtained when feeding the maximum power of the speaker according to the test sensitivity method. It is an indicator of the overall performance of a speaker. For example, the efficiency of the speaker unit, the material of the voice coil, the magnetic permeability of the magnetic steel, the heat dissipation, the material of the cone, the mechanical properties, and the like.
In large halls, outdoor, etc., where high sound pressure is required, it is undoubtedly necessary to select a speaker with a high maximum sound pressure value. Otherwise, multi-speaker stacking is used, on the one hand, the cost is not low, on the other hand, the interference distortion is increased, and the system is complicated.
Above we talked about several common technical indicators of the speaker one by one. Only by understanding their meanings can we make reasonable choices based on many factors. On the one hand, it achieves excellent performance, on the other hand, it saves cost and maximizes its benefits. It also meets the energy saving and emission reduction in the field of speakers, and the sustainable development of green. Of course, this is a flexible and comprehensive choice of factors, without uniform standards and models.
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