"Overweight bass in active speaker
Author: Wu Hongki Wu Hong Jing
General ultra weight bass refers to an audio below 120 Hz, and the height refers to an audio of 220 Hz to 100 Hz. Whether it is popular music or classic music, whether natural music is still in nature, heavy bass and overweight bass are less, but like MSG, it is essential, less it, music It will lack the sense of prevention.
Excessive bass is very strong. The directionality is not obvious, so the ultra-weight system.
Generally mono. In addition to the overweight bass in the latest digital recording, the overweight bass we currently hear is separated from the sound signal of the full-band. So, generally 2.1 active speakers are generally included in power, preamplifiers, crossover circuits, power amplifiers, speakers (speakers), as shown in Figure 1.
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1. The power of overweight bass channels is a first order or multi-order division. The frequency curve after the division point is oblique instead of the pressure-oriented right angle, the higher the step, the greater the slope.
In order to obtain a flat frequency response. The frequency coverage between each horn has a certain overlap.
At the same time, the impedance curve of the cone horn is also non-linear, the maximum resonant frequency point is at least 100 ~ 500Hz, with the rising frequency, and the impedance increases. This means that the signal of the speaker is different from the signal of different frequencies, like the power of the speaker. To make the sound pressure generated by each horn, the output power of the power amplifier that pushes the power amplifier of each horn cannot be equal, and there must be a certain proportional relationship.
For example, a 100W three-divided system with a divide point of 400 Hz and 3kHz. Then the bass channel requires 50W, the middle sound is 35W.
Tall-band is 15W, must be well-designed with this ratio, and the balance of the entire system is obtained by adjusting the insertion loss of the RC filter and the gain of the amplifier. For the heavy bass system, the power of the heavy and low sound channel is about 1 μm than the main channel, so the amplifier of the heavy and low sound channel requires a lot of power margin.
2. Division Network 2.1 Available Source Speed Box You can use active RC divide, or use passive RC divide, and active power division can also be used.
(1) The passive RC crossover passive RC electronic divide is simple, with the vertical frequency characteristics and phase characteristics, phase distortion and transient distortion are small, and the disadvantage is that the out-of-abandonation attenuation characteristics are not good. Only 6dB / Oct, which requires a speaker to still have good linearity outside the frequency turning point. That is to require an overweight bass speaker over 120 Hz, the medium and low speakers are still good linearity below 120 Hz. 2.1 speakers are all small caliber speakers, just able to make up for this shortcoming to maximize.
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Figure 2 is a first-order RC filter turtle.
The divide point is selected at 120 Hz, and the main channel is added to the attenuation of 10dB to balance the main channel and overweight. The amount of divided point and attenuation can be adjusted in practice. The input impedance of the RC division network is required is much larger than the output impedance of the source, and the output impedance of the RC division network is much larger than the input impedance of the power amplifier.
The output impedance of the signal source is generally less than 1 kΩ. The input impedance of the power amplifier is typically 47kΩ, the input of the RC division network, the output impedance is equal to the network resistance R. In Fig. 2, R1-1 and R1-2 are equal to the network resistor R, R2-1 and R2-2, and the resistance of R2-2 is also equal to R, 10 kΩ.
The calculation formula of the divided point is:
F0 = 1 / (2πrc) = 160 / (rc)
The network capacitance C in the formula is equal to the C1-1 and C1-2 and R1-1 and R1-2 are both network resistors in the cross-network network. It is also the attenuation resistance in the attenuation network, which is the same as the R3-1 and R3-2 in the right channel, and the sum of the two is maintained when adjusting the decrease.
If R1-2 is adjusted to a relatively small value, it cannot meet the needs, and the gain of the power amplifier can be adjusted to meet the needs.
If you want to get a steeper extracorporeal attenuation characteristic, it is best to adopt an active RC crossover network.
(2) The active RC crossover active RC frequency division circuit is multi-two Badwoz filter, with 12 dB / OCT out-of-site attenuation characteristics. If you want to get a more steeper, you can obtain a 24dB / OCT out-of-site attenuation characteristic in a two-stage series. The Badwoz filter requires its quality factor (q) in audio application to 0.707, and the C value in the RC network is not more than 0.1μF. Fig. 3 is a typical circuit that does not equal to 1, and Fig. 4 is a typical circuit equal to 1. To illustrate the problem, the components in the figure are values to 120 Hz according to the turning fold frequency (f0).
For a typical circuit of the gain (AO) is not equal to 1, the calculation is convenient, and R1 = R2, C1 = C2; for a typical circuit equal to 1, R1 = R2, C1 = 2c2 can be made. Such the Q value of the circuit will be independent of the value of R1 and C2, the calculation and adjustment of the circuit is more convenient. A bandpass filter can also be used in the main channel to filter out the impact of the super audio signal.
Figure 5 is a circuit of such a secondary bandpass filtering.
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Figure 6 is a 2.1 speaker frequency division circuit with loser, using 6 double operational amplifier NE5532 to complete the input buffer isolation, the separation of the heavy bass signal, the separation of the main channel and the overweight bass signal, output buffer, and the like.
Perfect performance, but this circuit is more complicated, if it is not rigorous, it will be counterproductive.
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In Fig. 6, IC1 B, IC2B will be separated from the left and right signal isolation buffer after the synthesis of the second-order low pass filter composed of IC3B to complete the separation of overweight bass signals.
The IC1a, IC2A passes the left and right channel signal isolation to the band pass filter composed of IC4A, IC5A, respectively. Filter out the super audio signal.
At the same time, it will play a delay to ensure accurate synchronization of the overweight bass channel, which is a major feature of this circuit. The signal is then sent from the inverter composed of IC4b, IC5B, and finally the subtractor composed of IC6A, IC6B, and is added to the separated overweight bass signal. The inverted full-frequency signal and the heave of the heave have been added to the left, right channel signal, clean and pure and pure and pure and pure.
This is another major feature of this circuit. This frequency division is substantially no phase interference, and the frequency dividing curve does not generate the phenomenon that the divided point fell and then intersecting, and there is no cause of the synthetic curve to appear in the peak valley or peak drum.
Figure 6 There is another feature of the circuit, one is added to the phase conversion circuit composed of IC3A and SW1. IC3A is an anti-van. When SW1 is up, it is obtained from the anti-tone signal; SW1 is downward, the in-phase signal is obtained. This can match the main speaker. The second is to join the low frequency signal upper limit frequency cutout point selection function controlled by SW2. That is, the turfline of the cutoff frequency of the second-order Badwater filter consisting of IC3B is controlled: 100 Hz, 125Hz, 150 Hz three frequencies. This approach asserts the adaptation of the circuit on the speaker speaker. It is also a way to regulate music. For recent independence, it should be a choice.
(3) Active power division This is an efficient frequency division method that combines power amplification and active divide. This approach does not require infant operation to play a stereotropic active device. In theory, the gain adjustable can be involute as long as the power amplification IC has two inputs opposite the phase. For example, our common TDA2030A, LM1875, etc. It is not suitable for the power amplifier IC like fixed gain such as TDA1517, TD7370, TDA8946. Figure 7 is a typical circuit. This method is actually putting the power amplifier IC to be used in powerful power. According to the value of the components in the figure.
The frequency turning point is 900 Hz, with an out-of-band attenuation characteristic is 18 dB / OCT. Pay attention to the active power divide, the resistance of R6 cannot be too large.
Figure 8 is a 2.1 circuit using active power divide. According to the parameters in the figure, the overweight bass channel can provide a power of about 56W. The primary channel can provide power per channel about 20W, with total harmonic distortion (THD + N) less than 0.05%. The divide point is selected for 220 Hz, which can be adjusted according to the actual situation of the speaker. The component selection of the components of the DVR network is less than 1%.
model
Power / W
distortion/%
Working voltage / V
Pin quantity
LM1875
20 × 1 (8Ω)
0.07
± 25
5
LM1876
15 × 2 (8Ω)
0.08
± 22
11
LM4766
30 × 2 (8Ω)
0.06
± 30
15
LM3886
38 × 1 (8Ω)
0.03
± 28
11
TDA2030
9 × 1 (8Ω)
0.5
± 14
5
TDA2030A
12 × 1 (8Ω)
0.08
± 16
5
TDA8946
15 × 2 (8Ω)
0.07
In
In one
TDA8947
18 × 2 (4Ω)
0.05
twenty four
In one
TDA1517ATW
6.6 × 1 (8Ω)
1
12
20
TA8231
17 × 2 (4Ω)
1
13.2
In one
3. Most power amplifier circuits used in the commonly connected circuit of the power amplification circuit are mostly an integrated power amplifier. The main performance indicators are shown in Table 1. The working voltage in the table refers to a typical operating voltage. Press "Press" The number of power per channel (access load impedance) "in the output power column (THD + N) means the power ... · column The nominal value is calculated, not the value in a 1W state. The data in the table is a data file from the manufacturer's disclosure. The integrated circuit of the general dual power supply can be operated in a single power state, and the two-channel integrated circuits can generally be connected to the form of BT1 to obtain greater power.
The author believes that although the sound quality of the digital amplifier cannot be comparable to the analog amplifier, it is suitable for at least for overweight bass channels.
Table 2 Reports more digital amplifiers.
model
Power / W
Different degree /%
Working voltage / V
efficiency/%
Pin quantity
Independent radiator
Output 1C filter
LM4651 + LM4652
125x1 (4Ω)
1
± 20
85
28/15
must
must
TPA3100D2
20x2 (8Ω)
1
In
92
48
not necessary
must
TPA3001D1
15 × 1 (8Ω)
1
In
86
twenty four
not necessary
not necessary
TASS012 + TAS5112
40x2 (8Ω)
0.2
29.5
90
48/56
not necessary
must
MAX9708
20x2 (8Ω)
10
In
87
56/64
not necessary
not necessary
MAX9709
25x2 (8Ω)
10
20
87
56/64
not necessary
not necessary
MAX9741
12x2 (8Ω)
1
In
78
56
not necessary
not necessary
TDA8920
50x2 (4Ω)
Be
± 25
90
In one
must
must
TA2022
100x2 (4Ω)
1
± 28
87
32
must
must
STA304 + STA500
25x2 (8Ω)
1
25
B2
44/36
not necessary
must
TDA7482
18x1 (8Ω)
1
twenty one
87
15
must
must
YDA143
12x2 (8Ω)
0.1
12
87
52
not necessary
must
AD1991
20 * 2
0.1
14.4
85
52
not necessary
must
About outputting an LC filter, part of the product can be used without coil inductance and porcelain capacitance, can be used.
4. Speaker 2.1 System Active Source Speaker General Super Low Sound Box With a long stroke horn with a 5 inches, the box is relatively large, the power and circuit parts are installed in the box, and the stereo uses small-diameter full-band horn. There is also a small amount of two divided varieties.
The speaker is structurally open, closed, inverted, tube, and forms of deformation on all kinds of basis. The author believes in the form of inverted and maze, the speaker uses push-pull form to achieve the effect of volume and performance. Inverted tongs improve the efficiency of bass, the labyrinth prolongs the road, equal to the volume increases the volume of the speaker, and the two trumpets make the push-pull method undoubtedly increase the bass energy. Figure 9 is an idea diagram of such a speaker. This approach is also called a double drive mode. Mitsubishi has successfully used it to use the overweight bass system of the TV. Use two models in the speaker. Antimeter connection. The impedance is half of the single speaker, the resonant frequency is the same as the single speaker. This way is theoretically to play low frequency of the same frequency. It only needs to collect half of the HJ single trumpet speaker volume. It can also cancel the quarter nonlinear distortion, the disadvantage is that the design and adjustment is very complicated, so the plastic material with very good performance consistency is relatively easy to achieve batch generation. "
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