April 2019 StudentZone Quiz Solution

Question:

Based on your measured data extract the L C and R for the speaker electrical model shown in figure 1 for the speaker you used. You can measure Rdc with the DC ohmmeter tool. Ignore LINPUT as it will be small compared to L. Enter these values into a circuit simulation schematic of the model and generate a frequency response sweep from 50 Hz to 1000 Hz and compare your model to the data you measured in the lab.

Answer:

Consider the plot of the calculated impedance:

We can extract from the plot the following information:

• F_s ~ 330Hz
• BW ~ 40Hz
• Rdc ~ 8Ω (see impedance value when frequency tends to 0Hz)
• R ~ 8Ω (at resonance Rdc + R ~ 18Ω)

Next, we can compute the values for L and C:

At resonance X_L=X_c, therefore:

 

Now, simulate the circuit with the computed values:

 

The plot of the calculated impedance can be computed using the formulas provided in the article.

As expected, the frequency response values are closer to the ideal ones.

Answer 1:

Consider the plot of the calculated impedance:

We can extract from the plot the following information:

• F_s ~ 330Hz
• BW ~ 40Hz
• Rdc ~ 8Ω (see impedance value when frequency tends to 0Hz)
• R ~ 8Ω (at resonance Rdc + R ~ 18Ω)

Next, we can compute the values for L and C:

At resonance X_L=X_c, therefore:

 

Now, simulate the circuit with the computed values:

 

The plot of the calculated impedance can be computed using the formulas provided in the article.

As expected, the frequency response values are closer to the ideal ones.