As we all know, bass is the basis of music signals, it affects the listening atmosphere to a great extent, the sound of the lack of bass signals will appear light and unreal, and in regular home theater playback, overweight subwoofers are an important part of If there is no subwoofer, it will completely lose the sense of presence, that is to say unreal. Many audiophiles generally use 6.5 to 8 inch woofer speakers. The lower limit of low frequency of these speakers is relatively low. Although the bass sounds powerful, the energy and extension ability are insufficient. Therefore, the author suggests that if conditions permit, it is better to choose medium and large floor boxes to get a richer low-frequency response, and when setting up a home theater, you should consider the subwoofer speakers. Of course, if the original system does not have rich low-frequency effects, you can also separately add a high-quality subwoofer to improve the replay effect. However, better subwoofers are expensive, and since we have the ability to design and make bookcases or floor boxes ourselves, can we also make a better subwoofer by ourselves? The answer is yes, interested Readers may wish to follow me to draw a scoop. The concept of an ideal subwoofer Before production, we should have a basic concept of what is a "better subwoofer". The author believes that there are several aspects of measuring the quality of subwoofers. Material selection, design and production Based on the above points of view, this DIY active overweight subwoofer will achieve the effect comparable to high-quality commodity machines through careful material selection and design. Suggestions for use In use, if the cut-off point of the low-frequency input is adjusted too high and overlaps too much with the low frequency band of the main speaker, the low frequency appears muddy and dragging in some frequency bands, which will affect the speed and clarity of the low frequency. On the contrary, when the cut-off point of the low-frequency input is adjusted too low, the low frequency will also appear incoherent, making people think that the main speakers and the ultra-low speakers are "worked separately". Therefore, choosing a reasonable low-frequency input cut-off point will make the main speakers and ultra-low speakers achieve a smooth low-frequency transition, the low-frequency volume will increase but will not feel too abrupt and rendering, so that the overall momentum is integrated. The general adjustment principle is that if the lower limit of the -3dB low frequency of the main speaker is 6O Hz, the 55 Hz low frequency input cut-off point should be selected, or it can be roughly adjusted in this way. If the woofer of the main speaker is 4 to 5 inches, 75 Hz low-frequency input cut-off point can be selected; if the woofer is 6 to 7 inches, 55 Hz low-frequency input cut-off point or lower can be selected.
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1. A good overweight subwoofer must be an active amplifier. The so-called "active amplifier" is a built-in amplifier, while a passive subwoofer does not have a built-in amplifier. There is only a passive crossover in the box. It must be shared with the main speaker or Another power amplifier. The passive subwoofer uses the volume control of the front stage to determine the volume. If the sensitivity or volume of the subwoofer is not equal to the main speaker, it will cause chaos in the sound field, uneven frequency response, and inability to locate the sound image. At this time, the positioning of the subwoofer cannot solve this problem, and these problems are difficult to improve. In addition, the vibration quality of the subwoofer large-diameter unit must be greater than that of the main speaker unit, so the sound speed is slower. After adding this subwoofer speaker, the effect is often very muddy.
Active subwoofer is specially designed for bass replay. Its working feature is that the signal goes straight into the pre-stage with source crossover. The frequency below 100 Hz is amplified by a dedicated bass amplifier to drive the subwoofer. The frequencies above 100 Hz are sent to the amplifier after being divided, and then amplified and broadcast by the main speaker. At this time, an independent volume control is needed to control the ratio of the subwoofer volume to the volume of the main speaker.
The regular addition of subwoofers is that the subwoofers work below the crossover frequency (for example, 100 Hz or 120 Hz), while the main speakers work above the crossover frequency, but such a crossover should be set after the output of the signal source. Before the main channel front stage, therefore, some advanced subwoofers are equipped with a pair of left and right channel output terminals, but in daily use, many people are directly connected to the subwoofer from the front stage output.
From this point of view, the unit and internal magnetic circuit structure used by the active subwoofer, the dedicated low-frequency boosting technology, as well as the crossover amplifier and cabinet are all for low-frequency reproduction. Therefore, the performance of active subwoofers is not comparable to passive speakers.
2. The volume of the ultra-low frequency should be sufficient, and the extension should be low enough. The function of the subwoofer is to make up for the low frequency of the main channel speaker.
3. It is well known that the subwoofer can withstand high power without distortion. The larger the area of ​​the diaphragm, the deeper the low frequency latent. At the same time, in order to achieve sufficient energy, most subwoofers are more than 10 inches. The larger the membrane, the relative mass will increase, and the movement of the unit is not easy to be controlled. At this time, a larger control energy and a stronger input power are required. Otherwise, the vibration and vibration of the diaphragm can not make it forbidden, and the sound will be blurred. If the speed of the unit's reaction cannot keep up with the speed of the music, it will cause distortion in the low frequency band, make the sound blurry, and also make the low frequency weak and insufficient. force.
4. A reasonably designed and solid box structure. The subwoofer is the most distorted frequency band in the speaker playback, but the low frequency band actually contains many details and textures. The low frequencies like the bass cello and the organ are not the same. Blurring a blind sense of "robustness", the super-bass with excellent performance can also easily hear various clever changes such as hall sounds, details and timbre. The fast-response sub-bass can reproduce the cohesive impact and effectively improve the analytical power And well connected with the middle and high frequency bands. The length, width, and height ratio and sturdiness of the cabinet will directly affect the subwoofer's detail clarity, analytical power, sense of speed, transient response, etc., so it cannot be ignored.
First of all, the woofer we selected is Hivi Hi-FiRESEARCH 12-inch W12 woofer (see Figure 1). It is characterized by the use of high-loss, high-compliance, ultra-thin, fatigue-resistant rubber folding ring and German KEVLAR reinforced paper-based composite diaphragm, with high heat dissipation coating, no eddy current loss, high load power 76 mm voice coil and High temperature resistant SV line and integrated high-density aluminum basin frame, its symmetrical magnetic field (SMD) drive system can reduce the mutual modulation of voice coil inductance and back electromotive force, plus the ultra-long stroke linear displacement design makes it withstand high power, Fo (resonant frequency) and Qts (quality factor, total Q value) are low, good transient, excellent low frequency response, full and powerful bass, high definition and resolution, high dynamics, low distortion, it is very suitable for Source subwoofer.
Several main relevant parameters of W12 woofer are: rated impedance 8Ω; resonance frequency (fo) 28 Hz; rated power 150 W (maximum 300w); sensitivity (2.83V, 1m) 90 dB; total Q value 0.42; vibration quality 89.7 g; equivalent volume (Vas) 156 L. Figure 2 is its structural size diagram.
After selecting the unit, the power level of the bass unit should be considered. In order to control the movement of the bass unit well, the author believes that the power output of the power amplifier should not be less than the 150 W rated power of the bass unit, but it should not be greater than its maximum 300W Input power, so the output power of the power amplifier used should be around 200 W (8 Ω). For a general listening room of tens of square meters, if the design is reasonable, this power is sufficient.
The power amplifier used in the subwoofer should not only have a large driving force, but also have a small transient distortion and a fast response speed. The constant current power amplifier drive used here uses linear components to feed back the current flowing through the speaker voice coil to the power amplifier input terminal, so that the amplifier drives the load with a fixed current, so that the nonlinear distortion or transient in the power amplifier is well solved. Distortion cannot be taken into account.
There are many advantages to using a constant current amplifier drive. First, the current input to the speaker voice coil is not affected by the impedance of the speaker, thereby simplifying protection and improving reliability; second, the feedback sampling voltage and the current flowing through the speaker voice coil. There is a linear relationship, there is no phase difference, and the transient distortion inside the power amplifier is reduced. The transient distortion index of the system depends on the transient characteristics of the speaker; it is a power amplifier that uses the output load characteristics to drive the load with impedance changes with frequency. The strength and resolution of the sound, the response speed is also fast. Figure 3 shows an active servo power amplifier for an overweight subwoofer. It is specially designed according to the relevant parameters of W12 woofer. This line can output RMS power of about 200 W. It is designed with negative feedback and constant current for upper and lower symmetry. The characteristic of this line is that negative feedback is added to the emitter of the input stage transistor separately and combined with their respective bias circuits to form an independent The upper and lower symmetrical lines have the advantage that the front stage transmitter is not easy to mix with noise, and the power amplifier has a high signal-to-noise ratio.
The design characteristic of the servo equalization phase and volume control circuit is that the signal output from the sound source or the previous stage is sent to the input terminal of the operational amplifier IC1A through the L and R inputs. The switches K1 and IC1B are used to control the positive and negative phase of the signal, so The main speakers have more correct phase matching. The circuit formed by the triple band switch K2 and IC1C is a low-frequency input cut-off point of about 40 Hz, 55 Hz, 75 Hz, and 100 Hz composed of Butterworth third-order low-pass filters.
Figure 3 Active servo power amplifier for subwoofers Figure 4 is a power supply diagram for active servo power amplifiers. Enthusiasts all know that good power is no less than the power line. In order to obtain better sound effects, the machine uses a high-quality R-type transformer of about 650 w. The magnetic leakage and efficiency of the R-type transformer are better than the common ring. Type or EI type transformers are better, and the temperature rise is lower. It is obviously superior to toroidal type or EI type transformers in the interior of an overweight subwoofer with a relatively complex operating environment.
The front and back processing lines of the machine each have their own independent power supply, and the windings are separated. Among them, the power supply of the control line adopts three-terminal voltage stabilization processing and outputs plus or minus 15V power supply to IC1 and IC2. Resistance, use 4 pairs of medium-capacity filter capacitors in parallel to get faster output. In order to further reduce the mutual interference of the magnetic field in the box, the entire active servo power amplifier is installed in a 30 cm × 35 cm × 9.5 cm thick aluminum metal case, in which the heat sink is installed on the outside of the box to facilitate heat dissipation.
After obtaining the volume occupied by the active servo power amplifier, we can easily find the volume of the inner cavity of the overweight subwoofer. From the perspective of several main relevant parameters of the W12 woofer, this unit is more suitable as an inverting box. In order to obtain a relatively flat rather than rendered low-frequency response, it has excellent transient response and good low-frequency extension. When using SC4 response design. The SC4 response design is a better choice in the design of the inverter box. Its characteristic is that the box is relatively large, but it has a very low tuning frequency and relatively excellent transient response and low distortion output characteristics. Some readers ask why not adopt a better SBB4 response design? SBB4 is certainly better, but after considering the relationship between the sound quality of the two designs and the size of the cabinet, we think that the SC4 response is sufficient to meet the high level of listening requirements.
Although the inverter box designed with SC4 response is good, it requires a low Q value for the woofer. The total Q value of the w12 woofer is 0.42, which basically meets this requirement. The overweight subwoofer is designed according to the table look-up method. Table 1 contains the design data of low Q value SC4 from 0.37 to 0.44. When designing SC4 with different Q values ​​to respond to the inverter box, readers can also use this data to design.
According to Table 1, we can quickly find the internal empty volume of the overweight subwoofer.
Find the empty volume Vb in the box:
Vb = Vas ÷ α = 156 ÷ 0.9113 = 171.2 (L)
Find the tuning frequency of the cabinet:
fb = (fh ÷ fo) × fo = 1 × 28 = 28 (Hz)
Find the low-frequency cut-off frequency f3 of the speaker:
f3 = (f3 ÷ fo) × fo = 0.937 × 28 = 26 (Hz)
Find the length L of the inverter tube:
Lv = 2350Dv2 ÷ (fb2 × Vb) -0.73Dv
Where Dv is the opening diameter of the inverter tube. In order to obtain a good linearity, the value here is 100mm. After calculation, Lv≈102.1 mm.
The value calculated according to the volume formula of the cabinet is the net volume. In actual calculation, remember to add the volume of the built-in power amplifier (about 10 liters) and the volume of the speaker (about 4 liters), and the volume of the reinforced support can be set At about 9 liters, in this way, the final volume of the cabinet V = 171.2 + 10 + 9 + 4 = 194.2 L, the actual cabinet size can be calculated according to 195 L.
The ratio of height, width and depth of the internal clearance of the cabinet is closely related to the sound quality. If the size ratio is not selected properly, it may cause two or even three axial vibration frequencies to overlap, resulting in standing wave interference that is difficult to eliminate, which makes the sound staining worse . In order to reduce unnecessary influence, the ratio of height, width and depth of this box is 1.3: 1: 1.2. After calculation, the height, width and depth of the internal clearance of the cabinet are 65 cm, 50 cm and 60 cm, respectively. The box is made of 25 mm thick medium density fiberboard (MDF). In order to improve the rigidity of the box, a support plate is provided inside the box, and the front baffle is bonded with two 25 mm thick medium density fiberboard (MDF). To reduce the noise caused by the resonance of the box board, get a clearer sound effect. Figure 5 is the production size of the speaker. Please pay attention to the processing of the contact surface of each baffle when making it. The joint surface should be coated with carpentry glue to make the contact surface tight, and tightened with wood screws to ensure that the joint is tight and tight. . In order to balance the weight of the front and rear baffles, the active servo power amplifier is set on the rear baffle, and the radiator is exposed. As can be seen from the layout of the rear baffle of the box, the inverted phase hole is opened in the back, that is, the box should not be too close to the rear wall when it is placed.
There are two methods for placing sound-absorbing materials in general speakers: the pasting method and the filling method. Inverted speakers often use the pasting method. The amount of sound-absorbing material in the box is about 5 cm thick wrapped in cotton cloth on the wall of the box. Mineral wool. If you feel that the low-frequency energy is too much, you can properly thicken the sound-absorbing material. In this way, the total Q value (Qts) of the speaker decreases, which can change the thickness of the low frequency, make the bass sound clearer, and improve the transient response speed. In order to get clear and high-resolution bass for the ultra-low speakers, metal nail feet should be used for this box, preferably copper foot cones.
Do not adjust the volume of the ultra-low speakers too much (it is best not to exceed 10 o'clock) to prevent the ultra-low bass from getting too loud and reducing distortion. When adjusting the phase, first put a piece of music with fuller low frequency, and then set the phase at 0 ° and 180 ° respectively. Compare the sense of volume of the low frequency at this time. It is better to have a full sense of volume, clear sound, and cohesion. When adjusted, the subwoofer has been integrated into the entire system, and you will feel its power.
It takes about 2,500 yuan to make an active subwoofer like this, but its sound effect is comparable to that of a commodity box that is twice the price, and it is really. Friends in need, might as well do it yourself.
Compare led grow light to traditional HPS/MH grow light
WHAT MAKE UP AN EXCELLENT LED GROW LIGHT ?
1.PPFD Value : PPFD is Photosynthetic Photon Flux Density. When you choose a plant light, you should compare the PPFD values of different plant lights. The larger the value, the better the growth of the plant.
2.Actual Power: Because the actual power of the plant light always varies with different conditions, all Amazon sellers use the rated power to describe the power of the product because the rated power is constant. When you pick a LED grow light, the rated power of the plant light is a reference, and more importantly is the actual power.
3.Core Coverage: In addition to the above two, when you choose a plant light, you also need to compare the cover area of different plant lights, of course, the size of the core coverage area. In general, in germination stage, you can hang the plant light higher and the cover area is larger. In flowering stage you can hang the plant light lower and the cover area is smaller because the plant needs more light at this stage. You have to compare different coverage areas to choose the plant light that suits you.
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