Regarding the design of the sound cavity of the horn, basically we stay on a concept without a complete set of theoretical guidance. The sound cavity design we know is often understood as follows:
1: There must be a sound cavity, which is used for sound reinforcement. As for why there is a sound cavity, I don't understand.
2: The sound cavity requires sealing. If the sealing is not good, it will cause poor bass.
3: The sound cavity hole can not be opened too large, if it is opened too much, it will cause the volume to become lower.
The above three points are what we are most concerned about. We often follow the requirements without asking why.
I try to use the RF theory to deduce the design of the speaker sound cavity:
Contrast between antenna and horn antenna, horn medium, vacuum air, electrical energy is converted into electromagnetic field energy, electrical energy is converted into sound energy, main device, antenna, horn, accessory device, antenna itself and matching circuit, sound cavity principle, electromagnetic wave theory, shock wave theory, purpose to obtain maximum energy output, suitable frequency response Maximum energy output, proper frequency response Conclusion Only suitable antenna and proper matching circuit can obtain maximum energy and proper frequency response. Only efficient speakers and suitable sound cavity can obtain maximum energy and proper frequency response.
From the above, we basically know that the horn and the antenna have a similar function, which is to play the role of energy conversion, in which the horn is the key device, it is the root of electrical energy to acoustic energy, but the sound cavity of the accessory device determines its maximum output power and Frequency response, next we mainly discuss how the sound system obtains the maximum energy.
To give an example, we patted the air with our hands, and the work done on the air is basically equal to 0. If we take a very large fan, the fan does not move, and the work done on the air is also equal to 0.
To do work on air is actually to sound the air. If this frequency is within the range that we can hear, it is sound.
Then the above example shows that there is a pole to work on air by hand, that is to say, there is a maximum value. We use the following formula to see:
P = F & TImes; V
P is power, the power to do work to the outside world, F is the magnitude of force, and V is speed.
This formula shows that F is too small, or V is too small, it is impossible to work externally, only the product of two values ​​determines the external power.
Next, let's see if the horn is the same as the hand, that is, a diaphragm plus a power coil, the diaphragm determines the size of the fan, and the power coil is equivalent to the human force.
Because the loudspeaker's diaphragm cannot be changed, unless you change a loudspeaker, in the case of the loudspeaker's diaphragm and the frequency of the power signal, we will describe how this sound system should increase the output energy:
Comparing P = F & TImes; V formula, we put forward a simple formula for specific work done by the speaker.
Because F is proportional to the diaphragm area (S), it is written as F = K & TImes; S, where K is the coefficient.
V is determined by the power coil of the horn. The power of the power coil is generated by the electric field. The resistance of the power coil is generated by two parts. One is the resistance of the air to the diaphragm (K & TImes; S). The elastic force is against diaphragm vibration (Fz).
For audio systems, K × S is generally much smaller than Fz. The reason is as follows. Looking at an audio system, it is 100W or so, and the sound volume is not much. It is said that a person sings loudly for a year, and the energy generated can only burn a pot of water, and the energy of the sound is still very little. In most audio systems, its energy is consumed by the speakers and heats up.
Therefore, air cannot affect the power coil, and V can be considered to be certain.
Then the formula becomes P = K × S * V
Because the signal is fixed, the diaphragm area S of the speaker is also fixed. If you want to change P, you can only change K. The purpose is to increase K. In fact, K is determined by the sound cavity, as follows:
If our current air density is doubled, then K is doubled. If only a part of the air is doing work, the generated force can be increased. This is because the aerodynamic principle dV / V = ​​dF / F Work on air in a certain space, the change of air volume is proportional to the change of force. This is the principle of the sound cavity, which is to draw a part of the air, increase the K value, and let the speaker do work on this part of the air to generate sound, and then this part of the energy is transmitted to the entire space, where the sound cavity is used as the middle of the energy transfer Link.
The above reasonably explains the first point mentioned above, why there is a sound cavity, which can be similarly analyzed for 2, 3, and for 2, the sound phase problem needs to be analyzed, because the speaker has two sides, which can be regarded as two Considering the sound source, the phase difference is 180 °. For the third point, it can be integrated into the first point, which affects the K value.
It is mainly designed for portable small sound chambers, such as mobile phones and walkmans.
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