# Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction
## 3 Experimental Verifications (Prototype)  
The experiment for measuring the SPL was conducted in an anechoic chamber. The electric wires were connected to the prototype 1610_SPK for the input signals, and the speaker was inserted into the speaker box with a back volume of 0.6 cc. The speaker was fixed with a baffle plate using clamps. The microphone for measuring the SPL was located at a distance of 0.1 m along the central axis of the microspeker.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Part** & **Material** & **Young’s Modulus** & **Poisson’s Ratio** & **Density** \\ \hline Coil & Copper & 126 GPa & 0.34 & 5321 kg/m\({}^{3}\) \\ Center diaphragm & Aluminum alloy & 68.9 GPa & 0.33 & 856.1 kg/m\({}^{3}\) \\ Side diaphragm & TPEE compound & 0.003 GPa & 0.42 & 1223 kg/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Material properties for finding the effective diaphragm area (\(S_{d}\)).  
Figure 9: Method of determining the effective diaphragm area and its boundary conditions: (**a**) effective diaphragm area and (**b**) boundary conditions.  
Sinusoidal signals ranging from frequencies of 100 Hz to 20,000 Hz were applied to the speaker with an input voltage of 3.1 Vrms. To obtain sufficient data in the overall frequency range, we used 1/12 octave for the input frequency resolution.  
The experimental system (B&K system) used for measuring the SPL consisted of a power amplifier (B&K, 2718), a microphone (B&K, 4191), and the PULSE Multi-Analyzer system (B&K, 3560C). In the B&K system, the sound signal from the microphone was transformed into SPL data in the frequency domain via a fast Fourier transform. The sampling frequency of the microphone was 48 kHz. Figure 10 shows the experimental setup and measurement system connections. Ten prototype 1610_SPK samples were used in the experiment, and the SPL was measured three times for each sample. The measured SPL was averaged at each tested frequency.  
The acoustic performance of the microspeaker at low frequencies can be represented by an arithmetic mean (average) of the SPL from four frequencies: 200 Hz, 300 Hz, 500 Hz, and 700 Hz. The average SPL of the prototype 1610_SPK from the four frequencies was found to be 77.92 dB. Table 5 shows the SPL of 1610_SPK at four frequencies and its averaged value.  
The simulation and experimental results for the overall frequencies are shown in Figure 11. The results were found to be well matched in terms of the SPL and displacement. This indicates that the analysis method can be used to predict and analyze other speaker models.  
Figure 11: Experiment and simulation results of 1610_SPK: (**a**) SPL and (**b**) displacement.  
Figure 10: Experimental setup and equipment connections for the SPL measurement: (**a**) experimental setup in an anechoic chamber; (**b**) B&K equipment connections.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Frequency** & **200 Hz** & **300 Hz** & **500 Hz** & **700 Hz** & **Average** \\ \hline SPL (dB) & 64.40 & 72.78 & 82.62 & 91.89 & 77.92 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Sound pressure level (SPL) of the prototype 1610_SPK at four frequencies.