Monday, March 14, 2016

Week Nine Blog

Week Nine Blog

1) Measure the resistance of the speaker.

The resistance measured using a DMM across the speaker is 8.2 Ohms. That means that this is an 8 Ohm speaker.

2) Build the following circuit using a function generator setting the amplitude to 5V (0V offset). What happens when you change the frequency?


 The sound exerted by the speaker would change when the frequency value would change. If the frequency increases the tone of the sound will also increase (the pitch gets higher). Likewise if the frequency decreases the tone will also go down (the pitch gets lower). Throughout all of this the voltage of the circuit is unchanged, voltage controls the strength (volume) of the sound so the volume remains unchanged when the frequency varies.

This is the video explaining sound changes from the frequency changing.

Here is a table describing the different observations found at selected frequencies:

Table explaining the change in pitch

3) Add one resistor to the circuit in series with the speaker (first 47 Ohm, then 820 Ohm). Measure the voltage across the speaker. Briefly explain your observations.


Table explaining our observations


4) Build the following circuit. Add a resistor in series to the speaker to have an equivalent resistance of 100 Ohm. Note that this circuit is a high pass filter. Set the amplitude of the input signal to 8V. Change the frequency from low to high to observe the speaker sound. You should not hear anything at the beginning and start hearing the sound after a certain frequency. Use 22 nF for the capacitor.


a) Explain the operation.

A high pass filter uses a capacitor in series with a resistor and a speaker. This configuration causes the high notes to pass through the speaker while the lower notes are cut out. When demonstrating how a high pass filter works, you will hear that at a certain frequency, the sound "cuts off" and you can no longer hear the lower notes. This is used in applications where a speaker sounds best at certain higher frequencies, and allowing lower frequencies to pass through will distort the sound.

This is a video showing the operation of the high pass filter


b) Fill out the following table by adding enough (10-15 data points) frequency measurements. Vout is measured with the DMM, thus it will be rms value.

This is a table showing our measured values of the high pass filter

c) Draw Vout/Vin with respect to frequency using Excel.

This is our plot of the high pass filter values of frequency vs vout/vin

d) What is the cut off frequency by looking at the plot in b?

Our plot did not have a big enough frequency range to see a certain cutoff frequency. By the looks of our plot, the slope begins to change towards 5.5 KHz. We expect the cutoff frequency to be somewhere after 5.5 KHz.

5) Design the circuit in 4 to act as a low pass filter and show its operation. Where would you put the speaker? 

The speaker is to be placed in parallel with the capacitor. Both of these come after the resistor, in series.

a) Explain the operation

A low pass filter allows the low notes to pass through the speaker, blocking out sound after a certain higher cut off frequency. The low pass filter is used in applications where a speaker sounds better with lower frequencies and will become distorted if higher frequencies are passed through it.


This is a video explaining the operation of a low pass filter


b) Fill out the following table by adding enough (10-15 data points) frequency measurements. Vout is measured with the DMM, thus it will be rms value.

This is our data table for the low pass filter

c) Draw Vout/Vin with respect to frequency using Excel.

This is our plot of our low pass filter data


d) What is the cut off frequency by looking at the plot in b?

Looking at our plot, it looks like the attenuation started around 1KHz or before it. Everything after these values is diminished voltage. From this conclusion, the cut off frequency seems to be somewhere before 1KHz.


6) Construct the following circuit and test the speaker with headsets. Connect the amplifier output directly to the headphone jack (without the potentiometer). Load is the headphone jack in the schematic. "Speculate" the operation of the circuit with a video.



This is a video explaining the operation of the circuit above. 






7 comments:

  1. Everything looks good on the blog. Nice job!

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  2. Everything looks well put together. I did notice you forgot to label your axis for the excel graphs. You may want to do this in future labs because you may get points deducted for that. Other than that nice job!

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  3. For question 3, why do you think the 820 ohm resistor produced an inconsistent sine wave compared to the 47 ohm resistor?

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    Replies
    1. The voltage value was so small it was hard to get a solid reading on it, you feelin me?

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