## 6 Results and Discussion  
First, the T/S parameters of microspepaker DSH742-005 have been obtained from the KLIPPEL measurement system (Figure 4) using laser vibrometry and are given in Table 4. These parameters define the specified low-frequency performance of a microspepaker. Other important parameters are also shown in Table 4.  
Figure 4: Schematic diagram of T/S parameter measurements of microspepaker using KLIPPEL measurement system. The frequency response curve of the microsp speaker without ventilation cloth are shown in Figure 5. The simulated and measured curves are in agreement before the second resonance. The frequency response rises monotonously until the fundamental frequency and becomes flat afterwards until the next resonance frequency. The obvious error between frequency response is at the peak and valley, 4-5 kHz. This difference may arise from the impedance value of the rear openings (vents) of the microsp speaker. It could also be due to the mode splitting of the diaphragm at high frequencies. Overall, based on the results, one can conclude that the ECM model of the microsp speaker has accurately estimates the preliminary prediction of the characteristics of the microsp speaker's frequency response. Thus, the validity of the proposed ECM circuit (Figure 2) has been established, which leads to further was investigated. The initial results of the PSO algorithm implementation in terms of the number of particles and the number of iterations, are shown in Table 5. The coefficients of variation after 30 numbers of particles were all close to 0, indicating that the set of parameters exhibits stable convergence. With selection of the combination of 30 particles and 50 iterations, the result of the upper and lower boundaries are shown in Table 6. Stable and convergent results were obtained in the boundary range of 10 times to 40 times. However the boundary range of 50 times was too wide, resulting in error. Therefore, 10 times boundary range was decided on for the inverse calculation of ventilation cloth parameters. The acoustic resistances of each type of ventilation cloth are shown in Table 7. \begin{table}
\begin{tabular}{c c c} \hline
**Symbol** & **Name** & **Value** \\ \hline \(R_{e}\) & Electrical voice coil resistance at DC (Ohm) & 30.81 \\ \(R_{2}\) & Electrical resistance due to eddy current losses (Ohm) & 2.16 \\ \(L_{e}\) & Frequency independent part of voice coil inductance (H) & \(1.35\times 10^{-4}\) \\ \(L_{2}\) & Para-inductance of voice coil (H) & \(1.08\times 10^{-4}\) \\ \(M_{ms}\) & Mechanical mass of voice coil and diaphragm without air load (kg) & \(1.01\times 10^{-4}\) \\ \(R_{ms}\) & Mechanical resistance of total-driver losses (N\(\cdot\)s/m) & \(2.2\times 10^{-2}\) \\ \(C_{ms}\) & Mechanical compliance of driver suspension (m/N) & \(1.0282\times 10^{-2}\) \\ \(Bl\) & Force factor (Bl) (T-m) & 2.467 \\ \(S_{d}\) & Diaphragm area (m\({}^{2}\)) & \(9.62\times 10^{-4}\) \\ \hline \end{tabular}
\end{table} 
Table 4: Thiele/Small (T/S) parameters of DSH742-005. Figure 5: Simulated and measured of the frequency response curves of the microsp speaker without ventilation cloth. Figures 6 and 7 present the measured and simulated results of the non-woven ventilation cloths, respectively. It can be observed from the measured curves that the influence of the type of ventilation cloth is mainly below 1 kHz. For comparison, the frequency response of microspeaker without ventilation cloth is also given. Below 1 kHz, the highest curve was for microspeaker without ventilation cloth and the remaining curves were progressively lowers as thickness of non-woven cloth increased. Moreover, the remaining curves tended to became relatively straight, facilitating ease of listening. The measurement curves with non-woven ventilation cloth exhibited flat frequency response after 1 kHz until the start of furious resonances. The sharp dip in the response without ventilation cloth was not evident among the remaining responses, ensuring the extension of the audible range to the microspeaker.