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--- university:courses:electronics:electronics-lab-speaker [05 Sep 2019 14:15] – Scopy snapshots for voltage and freq response Pop Andreea
+++ university:courses:electronics:electronics-lab-speaker [05 Apr 2023 18:43] (current) – [Background:] Doug Mercer
@@ Line 1: / Line 1: @@
-====== Activity: Measuring a Loudspeaker Impedance Profile ======
+====== Activity: Measuring a Loudspeaker Impedance Profile - ADALM2000======
 ===== Objective: =====
@@ Line 16: / Line 16: @@
 Knowing the resonate frequency and the minimum and maximum impedances are important when designing cross over filter networks for multiple driver speakers and the physical enclosure the speakers are mounted in.
+Dynamic loudspeakers are abysmally inefficient electro-mechanical conversion devices, as [[wp>Loudspeaker|Wikipedia]] substantiates: “Loudspeaker efficiency is defined as the sound power output divided by the electrical power input. Most loudspeakers are inefficient transducers; only about 1% of the electrical energy sent by an amplifier to a typical home loudspeaker is converted to acoustic energy.”  Yes, 1% is an abysmal efficiency as we try to “be more green”, but so far it is the best we have that sounds good (and each dynamic transducer only sounds good over a limited frequency range).
 ==== Loudspeaker Impedance Model ====
@@ Line 21: / Line 23: @@
 To help understand the measurements we are about to make, a simplified electrical model of a loudspeaker is shown in figure 1.
-{{ :university:courses:electronics:alz_f1.png?600 |}}
+<WRAP centeralign> {{:university:courses:electronics:loudspeaker_model.png?600|}} </WRAP>
 <WRAP centeralign> Figure 1. Loudspeaker Impedance Model </WRAP>
@@ Line 33: / Line 35: @@
 • F<sub>S</sub> is the resonant frequency of a loudspeaker. The impedance of a loudspeaker is a maximum at F<sub>S</sub>. The resonant frequency is the point at which the total mass of the moving parts of the loudspeaker become balanced with the force of the speaker suspension when in motion. The resonant frequency information is important to prevent an enclosure from ringing. In general, the mass of the moving parts and the stiffness of the speaker suspension are the key elements that affect the resonant frequency. A vented enclosure (bass reflex) is tuned to F<sub>S</sub> so that the two work in unison. As a rule, a speaker with a lower F<sub>S</sub> is better for low-frequency reproduction than a speaker with a higher F<sub>S</sub>.
-• R represents the mechanical resistance of a driver's suspension losses.
+• R represents the mechanical resistance of a driver's suspension losses. Part of the “mechanical resistance” in the system is the resistance of the cone to moving through the air, which happens to be the mechanical process that produces the pressure variations that we perceive as ‘sound’.
 ===== Materials: =====
@@ Line 44: / Line 47: @@
 ====Hardware Setup====
-First build the circuit shown in Figure 2, preferably using your solder-less breadboard. The loudspeaker can be in an enclosure or not. This configuration allows us to measure the voltage across the speaker V<sub>L</sub> using channel B voltage trace and the load current I<sub>L</sub> as the channel A current trace.
+Build the circuit shown in figure 2, preferably using your solder-less breadboard. The loudspeaker can be in an enclosure or not.
+{{ :university:courses:electronics:alz_f2.png?600 |}}
+<WRAP centeralign> Figure 2: Speaker measurement set up </WRAP>
 {{ :university:courses:electronics:loudspeaker_bb_voltage_meas.png?900 |}}
-<WRAP centeralign>Figure 2: Speaker measurement setup for V<sub>L</sub> and I<sub>L</sub></WRAP>
+<WRAP centeralign>Figure 3: Speaker measurement setup for V<sub>L</sub> and I<sub>L</sub></WRAP>
+\\
 ====Procedure====
 In Scopy, start the Signal generator and generate a sine waveform with 8V peak-to-peak amplitude and 100 Hz frequency.
-Using the Voltmeter tool we can calculate the speaker impedance Z at a single frequency by dividing the RMS voltage across the speaker (channel 1 RMS voltage) by the RMS current through the speaker, (channel 2 RMS current).  The RMS current can be computed as the RMS voltage on channel 2 divided to the parallel equivalent resistance of R1 and R2.
+Start the Voltmeter and set both channels to AC (20Hz-800Hz). Using the Voltmeter tool we can calculate the speaker impedance Z at a single frequency by dividing the RMS voltage across the speaker (channel 1 RMS voltage) by the RMS current through the speaker, (channel 2 RMS current).  The RMS current can be computed as the RMS voltage on channel 2 divided to the parallel equivalent resistance of R1 and R2.
 Try setting the signal generator to a few different frequencies and see how the voltage across the speaker and the calculated Z changes.
 {{ :university:courses:electronics:voltmeter_8vpp_100ohm.png?900 |}}
-<WRAP centeralign>Figure 3: RMS voltage across the loudspeaker</WRAP>
+<WRAP centeralign>Figure 4: RMS voltage across the loudspeaker</WRAP>
-You can plot the calculated impedance Z vs Frequency. The frequency of the signal generator is set in steps of 100 Hz and for each frequency you compute Z.  An example plot is shown in Figure 4. Your speaker will probably look different than this.
+You can plot the calculated impedance Z vs Frequency. The frequency of the signal generator is set in steps of 100 Hz and for each frequency you compute Z. The speaker impedance is small, approximately equal to the DC resistance in the linear region but is much higher at the resonance frequency F<sub>S</sub>.  An example plot is shown in Figure 5. Your speaker will probably look different than this.
+\\
-{{ :university:courses:alm1k:circuits1:alm-cir-laba11-fig5.png?600 |}}
+{{ :university:courses:electronics:plot_of_calculated_impedance.png?600 |}}
-<WRAP centeralign>Figure 4: Example Plot of Calculated Impedance</WRAP>
+<WRAP centeralign>Figure 5: Example Plot of Calculated Impedance</WRAP>
-The speaker impedance is small, approximately equal to the DC resistance in the linear region but is much higher at the resonance frequency F<sub>S</sub>.
-=====Frequency response of the loudspeaker=====
-In order to plot the frequency response make the connections as shown in Figure 5.
+=====Frequency Response=====
+====Hardware Setup====
+In order to plot the frequency response make the connections as shown in Figure 6.
 {{ :university:courses:electronics:loudspeaker_bb_freq_resp.png?900 |}}
-<WRAP centeralign>Figure 5: Breadboard Connections for plotting the frequency response</WRAP>
+<WRAP centeralign>Figure 6: Breadboard Connections for plotting the frequency response</WRAP>
+\\
 ====Procedure====
 In the Network analyzer tool you will do a logarithmic sweep.  Set the start frequency to 100 Hz and the stop frequency to 1 kHz. Set the phase to vary from -30 to 30 degrees and the magnitude from 0 to 10 dB.
@@ Line 78: / Line 85: @@
 {{ :university:courses:electronics:freq-resp_100ohm.png?900 |}}
-<WRAP centeralign>Figure 6: Frequency sweep of the loudspeaker circuit</WRAP>
+<WRAP centeralign>Figure 7: Frequency sweep of the loudspeaker circuit</WRAP>
-===== Directions :=====
-Build the circuit shown in figure 2, preferably using your solder-less breadboard. The loudspeaker can be in an enclosure or not.
-{{ :university:courses:electronics:alz_f2.png?600 |}}
-<WRAP centeralign> Figure 2 Speaker measurement set up </WRAP>
-Connect waveform generator 1, and the two scope channels to the loudspeaker circuit as shown.
-=====Procedure:=====
-Start the Scopy software. Select the Network Analyzer instrument. Set the start frequency to 10Hz and the end frequency to 1KHz. Set the amplitude peak-to-peak to 8 Volts and the offset to 0V. Set the max gain to 1X. Under the Settings drop down tab open the options window and set the settle time to 40 and the FFT window to cosine.
-A few words on why these setting should be adjusted. As the frequency is swept the AWG output is stopped briefly between frequency steps and the signal driving the speaker will be turned off. The speaker is a mechanical system with resonance and this step change in the driving signal will cause it to ring at the resonate frequency. In order to make an accurate measurement at the driving frequency we must wait for the ringing to die out. The amount of time needed will depend on the particular speaker being measured. The 40 mSec suggested above was the correct value for the speaker used in this example. Your results may vary depending on your particular speaker. Switching to the cosine window function gives a more accurate amplitude result.
-Hit the Run button. You should see the frequency response of the voltage across the loudspeaker and the current through the speaker (by measuring the voltage across the 100 ohm resistor). The data on the screen is plotted in dB so the vertical scale is not in volts. An example plot is shown in figure 3. Your speaker will probably look much different than this.
-<WRAP centeralign> Figure 3 Example sweep </WRAP>
-You can now Export the data, as gain not in dB to make the math easier, to a comma separated values file and load it into a spreadsheet program such as Excel.
-By saving the data as gain the signal generator amplitude (in volts) falls out of the equation.
-{{ :university:courses:electronics:alz_e1.png?300 |}}
-Where:\\
-G<sub>1</sub> is the channel 1 gain ( voltage across speaker )\\
-G<sub>2</sub> is the channel 2 gain ( voltage across 100Ω )\\
-A is the AWG amplitude\\
-You can calculate the magnitude of the speaker impedance is by dividing the channel 1 voltage gain by the channel 2 voltage gain all multiplied by the 100Ω resistor. An example plot is shown in figure 4. Your speaker will probably look much different than this.
-{{ :university:courses:electronics:alz_f4.png?550 |}}
-<WRAP centeralign> Figure 4 Calculated example impedance plot </WRAP>
-The speaker impedance is very close to 8Ω in the linear region but is much higher at the resonance frequency F<sub>S</sub>.
 ===== Questions: =====
@@ Line 128: / Line 97: @@
 ==== For further reading: ====
-[[http://www.analog.com/static/imported-files/application_notes/236037846AN_843.pdf|Measuring a Loudspeaker Impedance Profile Using the AD5933]]
+[[adi>static/imported-files/application_notes/236037846AN_843.pdf|Measuring a Loudspeaker Impedance Profile Using the AD5933]]
 http://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers
-**Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]].**
+<WRAP round download>
+**Lab Resources:**
+  * Fritzing files: [[downgit>education_tools/tree/master/m2k/fritzing/loudspeaker_imp_bb|loudspeaker_imp_bb]]
+  * LTSpice files: [[downgit>education_tools/tree/master/m2k/ltspice/loudspeaker_imp_ltspice|loudspeaker_imp_ltspice]]
+</WRAP>
+**Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]**

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