Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel Office: N319 ESC Tel: Office hours: on appointment Class website:

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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 the instructor, at with the following information: 1)Your name and section 2)Which lab ? (number or title) 3)When? (either regular lab time, otherwise specify)

Lab 13 Loudspeakers

Low-fidelity speaker High-fidelity 4-way speaker High-fidelity 3-way speaker

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

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

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

Cross-over network Goal: get a flat frequency response over wide range Cross-over network tweeter woofer For simulation, go to: High-pass Low-pass Result:

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

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

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

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)

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!!