What Are Proportional Dividers?

The analog crossover is a circuit device in the speaker, which is used to separate the input analog audio signal into different parts such as treble, midrange, and bass, and then send them to the corresponding tweeter, woofer, and woofer units for playback. The reason for this is that it is impossible for any single speaker to perfectly reproduce the various frequency bands of the sound.

Crossover

Analog crossover is a circuit device in the speaker, used to

Divider means

From the circuit structure point of view, the frequency divider is essentially

There are 8 terminals on the frequency divider for general vehicles.

The input English of the crossover is "INPUT"

Pick up

Most high-fidelity speakers are composed of two or more speaker units. To reproduce high-quality audio signals in the 20Hz to 20kHz frequency band, you must use the assistance of a high-quality crossover. Due to the different speaker units of each speaker, The crossover cannot be simply replaced, and it must be produced according to the characteristics of the specific speaker unit. A relatively complete set of design, production, and debugging methods is summarized, and only the producer is required to have a pure audio test signal containing 20Hz ~ 20kHz. The Hugo Gold Plate, a microphone signal amplifier circuit, a microphone and a digital multimeter without the need for special test equipment.

For amateur speakers, it is recommended to choose a two-way method.

First, the choice of crossover frequency f

The crossover point of the two-way speaker can be optimized between 2 ~ 5kHz. Generally, the crossover point frequency f is selected within a range above the octave of the woofer from the upper limit, and above the octave of the tweeter from the lower limit.

Second, the frequency divider and power allocation

The nominal power of the woofer and woofer constituting the speaker is different. In the power spectrum of the actual program signal, the proportion of high-frequency and low-frequency signals is also different. Therefore, after averaging the various signals, The power spectrum of the analog signal shown in Figure 1 is obtained. The power spectrum of Figure 1 is calculated, and the power distribution curve shown in Figure 2 is obtained. When selecting the frequency division point, it is necessary to consider the power distribution problem to make the treble The unit has some margin. Figure 2 shows that the total power of 20Hz ~ 20kHz is normalized to 100%, and the power occupied by 20Hz to a certain frequency f is a percentage of the total power. An application example is as follows.

For example, a two-frequency system with a frequency division point of 2 to 5 kHz, from the horizontal coordinate of 2 to 5 kHz in Figure 2 to the intersection of the curves, and the percentage is read from the vertical coordinate. The power ratio of 20 Hz to 2.5 kHz is 87%, and 2 to 5 kHz The power ratio of ~ 20kHz is 13%. When the total power is 100W, the bass power W is low = 100 × 87% = 87W, and the tweeter power W is high = 100 × 13% = 13W.

When using the above power distribution relationship, please also pay attention to the power standard of the speaker unit. General product labeling is rated maximum sinusoidal power (RMS), and some manufacturers mark the peak power or music power for commercial purposes, but the value is generally 2 to 4 times the RMS power.

Selection of frequency division method

Although there are several frequency division methods, such as 6dB / oct type, 18dB / oct type, 3dB drop point crossover type, 12dB / oct type, and 6dB droppoint crossover type, etc., considering their advantages and disadvantages, it is recommended to use 12dB / oct type.

Fourth, the crossover network

When designing a frequency division network, it is certainly best to add a load unit to the RC impedance compensation circuit as a constant impedance design. However, after consulting a large number of books and periodicals, I found that there are many calculation methods for the RC impedance compensation circuit. The RC value is also different, which makes it difficult for people to choose, so they have to design according to the frequency point resistance method.

First, use the circuit shown in Figure 3 to measure the resistance of the woofer and woofer at the crossover point (be careful not to replace the nominal impedance of the unit, otherwise the error will be very large, then perform the calculations in the upper right table and press the figure After the LC components are connected, the preliminary production is completed. The sensitivity of the woofer and woofer is unbalanced and can be adjusted by resistance attenuation (a special article introduced in the 15th issue of the "Electronic News" 1997). It is recommended to use high-quality polypropylene capacitors for optimization. Design the air-core inductor, and fix the component on the printed board with hot-melt adhesive. The inductor can be strengthened and fixed with cotton or plastic cable ties, and connected by means of shelf welding to make separate high-frequency and low-frequency channels. the way.

Five, debugging methods

According to the inverse square law of sound pressure level, the point sound source is in free space, the distance is doubled, and the sound pressure level is attenuated by 6dB. Using this law, the following actual operations can be performed.

Install the speaker body and speaker unit, without the crossover, use the "Hugo Gold Disc" test signal, and use the normal playback mode, with a fixed volume of 2 ~ 3W, and repeat the frequency f at the crossover point. 4 Self-made simple sound pressure tester, test the sound pressure at 2m, adjust the microphone volume potentiometer to make the digital multimeter read, an integer that is easy to memorize, write down the spare. Then, connect to the frequency divider low-pass network to change the sound The pressure gauge is placed at 1m, and the test reading should be the same as the last time, otherwise, increase (decrease) the capacitance by the large (small) reading until the reading is the same (the frequency f at this time is attenuated by 6dB). The signal is directly input into the woofer again, and the test signal is adjusted to an octave signal higher than the frequency f of the crossover point. The sound pressure is measured at 4m with a sound pressure meter, and the reading is recorded for backup. Finally, the crossover of the crossover is connected. Network, put the sound pressure meter at 1m, the reading is the same as last time, otherwise, slightly adjust (at this time, the octave frequency f is attenuated by 12dB), so that the bass network is debugged. Repeat the above operation steps for the tweeter network, adjust Inductor, pay attention to the input of the octave signal below the frequency f of the crossover point in the second step. In this way, a set of high-quality frequency divider is produced and The test is complete.

Generally, the frequency divider includes three basic parameters.

The first one is the frequency division point of the frequency divider. This should go without saying.

The second is the so-called path of the frequency divider, that is, the frequency divider can divide the input original signal into several signals of different frequency bands. What we usually call the two frequency divider and the third frequency divider are the frequency divider. "road".

The third is the "order" of the frequency divider, also called "class".

A passive frequency divider is essentially a complex of several high-pass and low-pass filter circuits, and the number of these filter circuits is the "path" mentioned above. But in each filter circuit, there are more elaborate designs. In other words, in each filter circuit,

Crossover

In the wave circuit, they can be filtered several times respectively. The number of times of this filtering is the order of the frequency divider.

The first-order frequency divider is also the structure of the sense-capacity frequency division, and each path in the second-order frequency divider has been filtered twice. This "double filtering" is the real meaning of "second-order"!

In fact, the term "second-order frequency divider" is not standardized, because "order" is not for the entire frequency divider, but for one of the "roads", so the strict term should be " The two-way frequency divider uses high-frequency and low-frequency second-order filtering. "Although it is not common, designs with high-frequency using second-order filtering and low-frequency using first-order filtering are also available.

In addition to the first and second frequency division, the passive frequency divider also has third, fourth and even sixth frequency division. The advantage of using a high-order frequency division is that its filter attenuation slope is greater, the frequency division effect is better, and it is also conducive to the design of the frequency division compensation circuit (because it is not the "divide" the more thorough and the cleaner the frequency divider is the good frequency division). In theory, the two signal curves after frequency division are superimposed on the original curve, which is really a good frequency divider), but the power loss of high-order frequency division is large, especially the phase effect is large. , Bad design will mess up the sound. So it is not better that the higher frequency is better.

Most of the 2.0 multimedia speakers on the market use capacitor or resistance-capacitance crossovers. Very few crossovers are used, and second-order crossovers are even less. For example, the shock wave SB-2000 uses a first-order frequency divider, while those using a second-order frequency divider are only Hivi T200A, M200, Edifier S2000, 1900TIII and so on. (Note: there are many high-end speakers that use second-order crossover).