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.

Multivibrator constituted by the transistors or integrated circuits. When switched on after the DC voltage from the multivibrator oscillator output audio signal, impedance matching device to promote the piezoelectric buzzer sound. Piezoelectric buzzer by the PZT or PMN piezoelectric ceramic materials. In the ceramic coating on both sides of the silver electrode by polarization and aging treatment, and then with the brass plates or stainless steel pieces stick together.

Magnetic buzzer by the oscillator, the electromagnetic coil, magnet, vibration diaphragm and shell and other components. When powered on, the audio oscillator signal current through the electromagnetic coil, electromagnetic coil creates a magnetic field. Vibrating diaphragm in the electromagnetic coil and magnet interaction, periodically vibrating voice.

First, visual: the former is very similar form as the county upwards of two buzzer pin placement, you can see the green circuit board is a passive buzzer, no circuit boards with vinyl A buzzer is active closed. However, this is only the preliminary judging criteria, but not the only criteria. With the continued development of the market need for quality requirements are increasing, many manufacturers now need to 12MM buzzer need Dibu sealing compound, Wen Ding sake of its performance and prevent core loss and other undesirable situation and so, visual preliminary identification method.

Here’s another way

Second, multimeter test: resistance with a multimeter test file Rxl file: buzzer with a black sheet document access “+” pin, red table pen back and forth to touch the other pins, if the trigger a cracking, cracking sound and the resistance only 8Ω (or 16Ω) is passive buzzer; if given continuous sound, and the resistance of a few hundred more than in Europe, is active buzzer.

3, DC voltage test; general 12MM general passive voltage 1.5V, active magnetic buzzer general voltage 1.5,3.0,5.0,9.0,12 V, corresponding with DC voltage input voltage (which can be transferred to large from small ), frequency about 2.7KHZ, can ring for active magnetic buzzer, does not directly affect the need to drive a square wave can ring for passive magnetic buzzer.

1, no do not ring before installation. – This is a quality in itself is a buzzer not work (the first one kind of buzzer such cases the probability of occurrence of more);

2, after welding when no sound or sound without sound. – This situation could be used in iron welding power is too large (suggested 20-30W soldering iron) or too long (recommended 3 seconds to complete a solder joint) causes the buzzer pin and coil weld heat melted Weld;

3, the welding process after the buzzer sounds out quietly, without sound or sand tone change. – This situation may start the buzzer of the current is too small or too large (buzzer normal operating current 20-30mA) can not lead normal tweet buzzer;

4, after a period of time using the buzzer sound or no sound change. – This situation may be too long tweet continuous buzzer (buzzer continuous period of not more than 8-10 hours a tweet, or become sound or burned) or the buzzer by the Central
Environmental impact;

5, after the buzzer wire welding work on board, there was no sound but the tone or removed to DC power supply test is no problem. – This situation may be subject to interference buzzer. Above five kinds of situations are most likely to use process buzzer malfunction, other faults are no longer made in this description.