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Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel

Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel Office: N319 ESC Tel: 801- 422-5687 kchesnel@byu.edu Office hours: on appointment Class website: http://www.physics.byu.edu/faculty/chesnel/physics145.aspx. Please help us improve the Phys 145 class.

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Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel

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  1. Physics 145 Introduction to Experimental Physics I Instructor: KarineChesnel Office: N319 ESC Tel: 801- 422-5687 kchesnel@byu.edu Office hours: on appointment Class website: http://www.physics.byu.edu/faculty/chesnel/physics145.aspx

  2. Please help us improve the Phys 145 class Answer the survey: https://byu.qualtrics.com/SE/?SID=SV_cMGHYuigPfbYTmk Thanks for your feedback!

  3. Make-up labs • Opportunity to make up for ONE missed lab • Labs available at same times than your regular labs: • - Wednesday April 11 • - Thursday April 12 • - Friday April 13 • If your prefer not to do it during reading days: • labs may also be available on Monday and Tuesday • Please email the instructor, at kchesnel@byu.edu • with the following information: • Your name and section • Which lab ? (number or title) • When? (either regular lab time, otherwise specify)

  4. Lab 13 Loudspeakers

  5. Loudspeakers Low-fidelity speaker High-fidelity 4-way speaker High-fidelity 3-way speaker

  6. Loudspeaker Cross-section Loudspeaker- resonator analogy Spring – mass resonator

  7. Loudspeakers Tweeter Medium Woofer (or boomer) High-frequencies 2 - 20 kHz Intermediate 500 – 5000 Hz Low frequencies 20 – 500Hz

  8. Loudspeakers- lab Woofer Tweeter High- pass filter Low- pass filter Our woofer frequency response to white noise Our tweeter frequency response to white noise

  9. High-pass Low-pass Result: Cross-over network Goal: get a flat frequency response over wide range tweeter woofer Cross-over network For simulation, go to: http://www.diyaudioandvideo.com/Calculator/XOver/

  10. Frequency Response Function Woofer Tweeter High- pass filter Low- pass filter Our woofer frequency response to white noise Our tweeter frequency response to white noise

  11. Manually sweep frequency of sinusoidal input • - and plot the FRF point by point • Use a sharp input pulse (flat Fourier transform) • - and look at the time response • Use a white random noise (computer generated) • - and directly get the FRF Frequency Response Function (FRF) Ways to measure the FRF of a loudspeaker:

  12. acoustic environment • microphone • power amplifier • signal preamplifier • … Potential contributions to non- uniformities in the FRF: Frequency Response Function (FRF) Chain of components contributing to the FRF

  13. Lab 13: Loudspeakers A. Measure FRF of a woofer and a tweeter • L13.1: connect all the components in the circuit (don’t forget the reference signal) • L13.2: Open Frequency Response.vi Send a white noise to the loudspeaker Read the FRF repsonse (Hanning sampling) • L13.3: measure and print the FRF of the woofer (0 – 10kHz) • L13.4: Play with loudspeaker enclosure to enhance low frequencies • L13.5: measure and print the FRF of the tweeter (0 – 10kHz)

  14. Lab 13: Loudspeakers B. Build a 2-way cross-over system • L13.6: Design a first order cross-over network that combines the woofer and the tweeter • L13.7: Build the cross-over network Measure and print the FRF Try improvments • 13.8: Connect you Ipod or mp3 player and listen to the music through your loudspeaker system!!

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