The last speaker design method mainly Nike U.S. Berry equivalent circuit method, what is the equivalent circuit law? Because the sound radiation, power vibration, oscillations in Differential Equations are the same, so the circuit will be replaced with a mechanical system, the sound system circuit instead, we are familiar with the circuit theory analysis, this alternative circuit such as effective circuit. Equivalent circuit of the speaker using a qualitative analysis, from theory to guide exploration in the experiment, this is the analog design.

The current design method is the use of advanced software and using computers to design: the finite element method analysis and design of the speaker, what is finite element method? The diaphragm is composed of many of the same nature as it is composed of tiny units, for each unit are the same for using the energy conservation principle to establish the balance equation of each node, solving equations, each node obtained displacement, and then solved by the node displacement of the strain throughout the unit stress. To obtain the vibration characteristics of the diaphragm. Finite element method using the advanced computer technology, as long as the input of various data calculated by the computer can quickly get the results, the design of the speakers into a problem using software to realize the reality of speaker design computable. Have a variety of software at home and abroad, such as we are using: Femm (magnetic circuit design software) and FINEMotor (speaker voice coil unit of magnetic systems and design software – Denmark), by these two software applications, from the design software we have tasted the sweetness of use, but for FINECone (finite element method, cone-shaped diaphragm dome basin and the acoustic characteristics of the simulation software – Denmark), we have not mastered the use of, so they use also need some time. Loudspeaker design software in China has been recognized more and more manufacturers and use. We believe that the speaker is a wise use of computer-aided design, design software application will improve product development level, will shorten the product development cycle and reduce costs. We asked designers emulated the design phase as soon as possible from the transition to the use of computer software design stage, to keep up with the times, improve product design level.

Electric speaker works:

When the speaker at work, we see it in the upper and lower diaphragm vibration, the vibration force to the upper and lower diaphragm is the electric power, both current carrying conductor and magnetic field interaction between its size: F = BLI

F – the instantaneous value of electric power N (Newton)

B – gap magnetic flux density T (Tesla)

L – coil wire length M (m)

I – Instantaneous current intensity A (ampere)

Voice coil in a magnetic field the force, according to Fleming’s law to determine the left hand. Four fingers left thumb and the rest of the vertical, so that magnetic field lines across the palm of the hand, four fingers point to the flow of current, then the direction of thumb force direction both for the voice coil, if the change in current direction, the direction of F change. Voice coil under the action of the electric power up and down movement, vibration drive cone, cone speed of the input vibration frequency, vibration amplitude and the strength of the input current. Cone vibration occurs when the vibration excitation of the surrounding air, forming a sound wave, introduced the human ear, is what we hear. Speaker completed by the electrical power → → sound conversion.

Speaker classification, because different starting point, cut into different angles, different methods can be classified on the speaker:

According to the principle: electric, electromagnetic, piezoelectric, electrostatic …

By working band: full band, language section, bass, alto, treble …

By radiation: direct radiation type, number cylinder, headphones …

By the magnetic circuit forms: the magnetic type, external magnetic, double-magnetic, internal and external magnetic composite …

By diaphragm shapes: flat-shaped mold, sunflower-shaped, conical, dome-shaped, …

By diaphragm material: polyester film, paper cone, aluminum, titanium film …

We are now making mobile phones receiver, the use of space requirements and specific conditions of the past, the receiver has a different structure, after the shelves for the base damping is not in fact, the damping for the front cover are often used in fine mesh, which actually increased the production of the difficulty, that is, we often talk about the more difficult the more simple structure of production, because the device more adjustable quantity, the error parameters can compensate each other. For example: the receiver diaphragm f0 trace differences in the value of the trace B floating magnet and so the method can be used damping cover off. So designers in the design of products must be carefully carried out process design, we speak to give their own burning our bridges, to ensure the feasibility of mass production.

We know that buzzer, speaker of the PA cavity design, is often understood as follows:

1: to have sound chamber, from the PA with, as to why should tone chamber, not sure.

2: Sealing Tone asked if the seal is not good, then lead to poor bass.

3: Tone hole can not open too much, too, if open, will lead to smaller volume.

Buzzer, horn antenna with a similar function, namely, the energy conversion from the action, the speakers, the key device, which is the electrical energy to sound energy is fundamental to sound chamber Danshi subsidiary device determines its maximum output power and frequency response, then We discuss the sound system down is to get the most energy.

First give an example, we slapped the air, the air acting essentially equal to 0, if we take a particularly big fan, fan does not move, doing work on the air is equivalent to 0.

The fact is that doing work on the air the air occurs, if the frequency range we can hear is the sound.
Then by the above examples, we can hand a pole on the air doing work, that there is a maximum. We look at the following formula:

P = F × V

P is power, the power of doing work on the outside, F Weili size, V is velocity.

Note that the formula F is too small, or V is too small, they can not do work outside, the product of the decision only two values of external power.

Next we look at speaker is not the same as with the hand, is a diaphragm plus a power coil, diaphragm decide the size of fans, power coils correspond to the force.

Because the speaker’s diaphragm is not possible to change, unless another speaker, the speaker diaphragm, the frequency of power signal certain circumstances, to describe the sound system should be how to improve the output energy:

Contrast P = F × V formula, we do work outside speakers present a simple formula specific.

Because F is proportional to the diaphragm area (S), so written as F = K × S, K as the coefficient.

V decision by the speaker of the power coil, coil power from the electric power generation, power resistance of the coil produced by the two parts, one of air resistance on the diaphragm (K × S), against the diaphragm vibration, but the speaker’s own diaphragm the stretch against the diaphragm vibration (Fz).

The sound system is generally much less than K × S Fz. The reasons are as follows. See a sound system, at every turn is like 100W, but the size did not sound much, is said to loud singing of a person for a year to produce energy can only burn a pot of water, visible, or very little sound energy, and must Most of the sound system, its energy consumption are on the trumpet, the heat.

So air can not affect the power coil, V must be considered.

Then the formula becomes P = K × S * V
because certain signals, the speaker diaphragm area S has a certain, If you want to change the P, the only change in K, the purpose is to increase K, in fact on the tone chamber K decided as follows:

If we double the current air density, K doubled, if only part of the air acting, you can enhance the force generated, because the aerodynamics dV / V = dF / F, which means that some do work on air space, air volume change with the change of power is proportional to. This is the sound cavity theory is to set aside part of the air, improve the K value, the speakers do work in this part of the air to produce sound, then this part of the energy and then spread to the whole space, here regarded as a sound chamber energy transfer Zhong Jian link.

More reasonable explanation of the above-mentioned first point, why should PA chamber, 2,3 can be similar to the analysis, for 2, still need to analyze the sound of the phase problem, because the buzzer, speaker there are two sides can considered as two sources, phase 180 °, for the third point, can be integrated into the first point, the K values are affected.

Targeted at small portable sound chamber design.

A, lead-free :280-290 degrees;
B, a lead :330-350 degrees;
Substrate (copper / iron / steel) General welding time: 3S
Silver surface of general welding time: 1.5S

(1) soldering iron before use, use multimeter to check resistance between the plugs should be 2 ~ 3kΩ. Then multimeter check the resistance between the plug and the metal value, multimeter gauge needles should be fixed, or should be thoroughly checked.

(2) Tip the general use of copper materials. For the protection of the welding of high temperature oxidation not rust, and often will tip after plating, and some also use easily tip the oxidation of alloy material. The new welding tip preceded by the official for tin plating. Method is to use fine sandpaper tip clean, then dip one pine fragrance, soldered in a hard object (such as wood) on the ground repeatedly, so that each side all the tinned tip. If you use a very long time, tip oxidation has occurred, use small rasp file to the light surface oxidation layer, the light in the exposed copper tip after the tin with the same with the new method of processing.

(3) the use of electric irons, if not the solder melting temperature is too low, or to completely melt the solder joint is not ugly or welding is not strong, the temperature is too high it will make iron, “burned to death.” We would also control the time a good weld, electric iron stay was too short, not easy to completely melt the solder, touch, easy to form, “Weld”, and welding time is too long, and easily damaged parts or make printed circuit board copper foil tilt. General 1 ~ 2s within a solder joint to solder well, if not complete, should wait a while longer welding time. Welding, soldering iron can not be moved, first chooses the location of contact with solder joints, and then tip the hot surface to contact with tin solder.

(4) electric iron plug is best to use three-wire plug, make the case properly grounded. Check carefully before using the power plug and power cord for damage, the tip is loose.

(5) electric iron is strictly prohibited in the course of any percussion, soldering iron over the head, the available cloth to wipe off.

(6) welding process, the electric iron can not leave around everywhere, not soldering iron should be placed on the shelves.

(7) The power cord can not take the iron head to prevent scorch the insulation layer of the accident.

(8) After use, should be promptly cut off the power, cooling, electric iron and then to recover the toolbox.

(9) welding is completed, the circuit board to use alcohol to clean the residual flux, to prevent carbon flux after the impact of circuit work.

8 ohm speaker arising from the resonance in the 400Hz, its resistance increased from 8 ohms to 10 ohms, at 10KHz, its resistance began to increase, to 1MHz, 100 ohms. In the absence of the audio signal, the final output is a symmetrical square wave, although speaker impedance of 100 ohms, it still consumes power, it will reduce efficiency. Moreover, because high-frequency pulse signal when added directly to the trumpet, will cause more serious RF radiation. When the speaker lead longer, the lead will show distributed capacitance, on the one hand makes the signal sent to the weakened, on the other hand will increase the radiation. These are not promising.

So, usually, or want to add a filter at the output. If the high frequencies, showing capacitive load, then an inductor in series can improve its properties. The series inductance high-frequency components can not flow to the load, thus reducing the radiation, but also improve efficiency. We can simply assume that the inductor should be at 30KHz when the inductance is equal to 8 ohms, which can calculate the inductance value is 42.4 uH.

If the D class amplifier in 250KHz switching frequency, then this frequency, its inductance is 66.7 ohms, the impedance of speakers by about 8 times a large. Therefore, it is the loss in the switching frequency is not very serious. It should be noted that the inductor because the current flowing through the relatively large, so thick the wire should be used. If the 8-ohm on to produce 1.2 watts of power, then the current is equivalent to 387mA (rms), the peak current will reach 550mA. Must ensure that such a large current, the inductor will not be saturated and reduced inductance. If the switching frequency is increased 4 times to 1MHz, then the inductance can be reduced four times, became 10uH. At this time the inductor size can be reduced, but increased frequency since its efficiency will be reduced, the distortion will be increased.

Only a series inductance and high-frequency radiation can not effectively solve the problem. Sometimes it even makes the electromagnetic radiation is more severe. Electromagnetic radiation is more sensitive in portable products. Because it may interfere with the machine to the other RF circuits. In order to reduce the high frequency radiation must also re-use a parallel capacitor to filter the signal directly to radio frequency interference.

1, according to the principle of sub-drive mode can be divided into: active buzzer (includes driver circuits) and passive buzzer (external drive);

2, according to the different construction methods can be divided into electromagnetic and piezoelectric buzzer buzzer;

3, according to the different packages can be divided into: DIP BUZZER (buzzer pin) and SMD BUZZER ;

4, according to the different currents can be divided into: DC and AC buzzer buzzer, which, in DC the most common users of communication in general is a direct drive electric voltage is generally 220VAC, 110VAC
Of course, the piezoelectric buzzer is used 220VAC’s.

Piezoelectric buzzer as the audio signal generator has a wide range of applications, because they are low power, voice clear and penetrating. Buzzer drive circuit or from an external drive circuit requirements oscillations in the resonant frequency of the piezoelectric element. Piezoelectric elements in its resonance frequency to provide maximum sound pressure output. However, the resonant frequency of a piezoelectric element has the greatest tolerance of ± 15%. Therefore, tuning to the nominal frequency of the external drive circuit is likely to lose the actual resonance point. This design is a piezoelectric element of the external drive circuit, it will automatically find the actual resonant frequency.

Works as follows: When a piezoelectric element at both ends of an AC voltage applied, the elements begin to vibrate. If you remove the excitation voltage, the vibration damping in a way will continue until all the stops. The residual vibration in the two ends of the piezoelectric device to generate damped oscillation. If the excitation signal close to the resonant frequency, the vibration will be stronger and will last much longer residual oscillation. Determine the actual resonant frequency is to try all the nominal frequency near the resonant frequency, and compare the duration of the residual oscillation.

In this design, Microchip’s PIC18F452 microcontroller, through its I / O pin RB4 and RB3 drive piezoelectric elements. Zero at the beginning RB3, RB4 is set to 1, the two flip each half cycle, resulting in a changing 0V DC offset of the piezoelectric voltage (VP). In 10 cycles, RB3 remains low, RB4 is used as an input for the statistical VP of low – high and high – low conversions. Port B Enable “Port Change Interrupt” function of time 10 ms, and the interrupt service routine in a counter reading increases, the number of statistical changes in the piezoelectric voltage. Listing 1 demonstrates this feature. Program on all possible frequencies repeat these steps and determine the number corresponding to the maximum conversion frequency, which is the resonance frequency. This method can be easily extended to multi-resonant frequency situation.

DB (decibel) is mainly used for measuring short dB decibel sounds, commonly used dB that is the sound pressure level of the size of the unit.

sound pressure per doubling of sound pressure increase of 6 dB magnitude. “Sub” means one-tenth digit is a “shell”, but generally only use dB.

0 db in the standard setting is based on people with normal hearing can hear the smallest sound determined.
In general, the greater the number of decibels the sound represented by the larger, the calculation is per decibel increase of 10 decibels, the sound is the original size of about ten times. That is, 20 dB 10 dB sound power is the power of ten times, 30 dB, 20 dB sound power is ten times the sound power rate, and so on. 100 dB is equivalent to the voice of the train, 120 dB is equivalent to the aircraft cited pounding.