When the headphone plug is barely connected to the outside world, the sound pressure received by the human ear is proportional to the vibration volume displacement of the speaker unit; in the case of a leak, the volume of the sound pressure received by the human ear and the vibration volume velocity of the speaker unit In proportion to the leak; serious or similar speaker radiation, the sound pressure received by the human ear is proportional to the vibration volume of the speaker unit.
For ease of explanation, changes in the vibration of the speaker under different leak conditions are not taken into account (actually, but without affecting the conclusion), ie, the amplitude does not change. Loudspeaker unit vibration volume displacement = volume velocity / angular frequency = volume acceleration / angular frequency squared, so the low frequency is exacerbated under plug-in conditions. The figure shows a comparison of the frequency response curves of earbud earphones with different degrees of leakage, which is very obvious. Another diagram shows the source of the leak.
Here's an example of an analogy:
Headphone sounding - The process of human ear reception can be seen as a hand plugging the needle exit. The plunger of the syringe corresponds to the speaker unit of the earphone, and the skin covered by the hand at the outlet corresponds to the tympanic membrane. If the syringe is not leaking, push the syringe piston to compress the air inside the cartridge. The hand is covered at the outlet to feel the pressure increase. How much the piston is pushed and how much the pressure rises.
If the syringe leaks, it will slowly push the piston, and will not increase the pressure inside the syringe, the hand will not feel the pressure change; and quickly push the piston, despite the leak, the hand can still feel the pressure changes. In other words, the movement of the piston during the leak of the syringe is more intense to cause the pressure in the syringe to change, and the hand covering the outlet feels this change.
PS The explanation above is simplified for ease of description. It is not strict enough. Those who are interested can learn by themselves.
In view of the fact that many of my friends do not understand the difference between headphones and speakers, I have posted a few pictures here to show the basic principles. Interested friends can have a look:
The first is the sound pressure of the speakers in a free field. As shown by the formula in the figure, the sound pressure p produced by a speaker at a certain point is proportional to the volume acceleration VolAcc. At the same time, attention is paid to seeing that the monopole radiation is a spherical wave, and the sound pressure is inversely proportional to the distance.
Look at the simplified model of headphones working in the ear canal. The situation at this time is similar to a pressure chamber with no leakage, the internal sound pressure p is proportional to the volume displacement S*x, and note that the sound pressure in the pressure chamber is uniform under the long wave approximation, not like freedom. The field is geometrically attenuated with distance. If there is a leak, it is approximately proportional to the volume velocity.
Therefore, the working methods of headphones and speakers are still very different, which also results in differences in both design principles and evaluation. Finally, affixing a form is an elaboration and comparison of some basic concepts of headphones and speakers:
Note: The above screenshots are from CA Poldy. Tutorial AES 120, Paris, May 2006 - Headphone fundamentals
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