Small speaker with high SPL?

In order to increase sound pressure level, we need to vibrate more air molecule by more power under unit time.For the two sizes speakers, the area of diaphragms of the 15mm speakers are around 176mm square (7.5*7.5*3.14),and the 20mm size speakers are around 314mm square(10*10*3.14). The 20mm speakers are only bigger by5 mm/ 25%, however, the diaphragm are bigger by 78%. Therefore when we input the same power, the 20mmspeakers can vibrate more air at the same time, and it result in higher sound pressure level.Generally, the speaker in bigger size can provide lower frequency response which is better for human’saudition. On the other side, we can also provide the smaller speakers more power to make higher soundpressure level, but it is limited by,1. Acceptability of the diaphragms2. Thermolysis of the speakers3. After increasing the power, frequency response will change too(because thicker diaphragm, heavier coil..etc)Therefore, what we can do is reform the material and the structure of the speakers to increase sound pressure level,but if it is possible to choose the bigger size, the problem of the lower sound pressure level will be improved immediately.

Acoustic keyword

W ( Watt ): A watt = a voltage x an ampere. For example, 330 Watt= 110V x 3 A.
V ( Voltage ): V is the unit of voltage, when it needs one joule of work to sent one coulomb of electric from one point to another point, then the potential difference between these two points is one voltage. 
Ohm: Ohm is the unit of impedance in electronics, the higher the impedance is, the less electric current can pass through. 
Hz( Hertz): The frequency of the sound waves vibrate every second. For instance, 100Hz means 100 times vibration in one second. 
dB ( Decibel): dB is the unit of the sound pressure level, which is calculated with logarithm, because the susceptibility to the sound of human ears is not linear. 
Fo ( Resonance Frequency): Fo stands for the resonance point of the speaker. The lower the Fo is, the efficiency of the low frequency is better. 
S.P.L. ( Sound Pressure Level): The volume of the sound. 
Vo-p: The measurement from Vo to the peak, to drive the magnetic buzzer, the waveform is 1/2 square wave. 
Vp-p: The measurement from peak to peak, to drive the piezo buzzer. The waveform is square wave.

Microphone Sensitivity

The sensitivity of the microphone is one of the most important factors, which affects the receiving result. The higher the sensitivity is, the higher the SPL can be received.Different from the production process of other products, the microphone is selected and sorted by its sensitivity after producing. We cannot get 1000pcs of what we need in sensitivity from just inputting 1000pcs of microphones’ material on the production line. Therefore, in order to avoid discontinuing the production, we had better choose the spec. usually with the sensitivity of -40 to -44, which is popular and easily produced.About the volume, we can still improve it by modifying the circuit, such as the impedance, the voltage, and the amplification factor.We suggest that do not choose a special spec. with very high or low sensitivity at first, or the problem of lead time and lacking of material might happen.