1. Physics 434 Module 3 - T. Burnett 1 Physics 434 Module 3 Acoustic excitation of a physical system

2. The theme of the next three weeks This week: operate in the frequency domain For a given frequency, what is the response? (resonances, etc.) Next week: time domain Excite with a pulse, measure response Following week: fourrier transform Relate to frequency domain measurement Physical system (the tube) Input signalOutput signal

3. First, a little pre-test Physics 434 Module 3 - T. Burnett 3

4. 4 Goals for this module Control and monitor an applied frequency Detect and measure a sound wave Generate set of RMS values vs. frequency Fit resonances to determine resonant frequencies and Q values Check speed of sound from resonance difference

5. Physics 434 Module 3 - T. Burnett 5 Step 1– just electronics Signal generator speaker ‘scope: microphone Breakout box ach0/ach8 dac0 Microphone, speaker Amplifiers tube

6. Physics 434 Module 3 - T. Burnett 6 Step 1, cont Adjust amplifier gains for given input (1 V) so that output does not saturate between 500 and 2000 Hz Note the resonant frequencies for later check

7. Physics 434 Module 3 - T. Burnett 7 Step 2 – test the output Get SoundGenerator.llb from web Note that it contains several VIs: SoundGenerator(select) Generate a continuous signal with selectable frequency SoundGenerator(sweep) Generate a sequence of discrete frequencies acquire_test Monitor and measure the signal acquired by the DAC Look at the output on the scope, verify the frequency, feed it to your microphone, verify that it does not saturate.

8. Physics 434 Module 3 - T. Burnett 8 The AT-E board 2048 512

9. Physics 434 Module 3 - T. Burnett 9 Step 3 – check the data acquisition Another self-contained VI, acquire_test.vi, acquires a waveform, with adjustable sampling rate and sample size.. The output is graphed and analyzed by a simple- minded RMS vi. Check that the RMS of the signal generator output, or the output from the DAQ card is stable and does not vary with input frequency (500-2000 Hz). (We do not actually measure this, but assume that it does not change.

10. Physics 434 Module 3 - T. Burnett 10 Step 4 – assemble your VI and run it Easy to cut and paste from the two test VI’s Must create a table of (actual) frequencies and RMS response from the microphone, with constant input to the microphone. Display on an XY graph Write to an file with the “Write To Spreadsheet File” vi from the All Functions | File I/O menu.

11. Physics 434 Module 3 - T. Burnett 11 Step 5 – Analyze the resonance peaks This is a new VI that you must write, capable of reading data from the file and fitting it: see test_resonance_fit.vi, with sub-vi resonance_fitter.vi for the fitting piece that you may use. Note: it must select a range over which the resonance is valid. The formula: Watch for this guy! This part sets up the demo

12. Physics 434 Module 3 - T. Burnett 12 Submit your vi’s in an llb Save plots with current value Use documentation for descriptions. Analysis VI should have a table of the resonance parameters, and your estimate of the speed of sound