2.1 Pressure acoustic
A method which is able to quickly evaluate the performance of a receiver in the pressure field of IEC 318 standard can be built by COMSOL Multiphysics. The IEC 318 standard is the type 1 artificial ear which is defined for simulating the acoustic load of the human ear under no leakage conditions and its frequency bandwidth of application is from 100Hz to 4KHz. The sound pressure level and impedance versus frequencies in pressure field can be calculated in advance to see if there are the requirements need to be achieved.
The IEC 318 coupler the air volume is around 2 cubic centimeters.
The back volume of the receiver, the diameter of the receiver is 40 millimeters. Both IEC 318 coupler and back volume is totally sealed without any leakage.
The Thiele Small parameters will be set on the effective diaphragm area of receiver (Sd).
To calculate the acceleration that couples with both IEC coupler and back volume in pressure field, and then the frequency response and impedance curve.
The total acoustic pressure and S.P.L. distribute inside the coupler can be evaluated as well.
The sound pressure level and impedance versus frequencies are the simulated results. Unlike speakers perform in free field, the sound pressure level in low frequencies are easy to be accumulated in pressure field especially without any leakage. Some headphone designs will arrange proper leakages to decrease the S.P.L. in low frequencies for the sound enhancements in mid and high frequencies. All kinds of design are able to be predicted by building the simulation models.