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

Thanks for your feedback!

Answer the survey:

https://byu.qualtrics.com/SE/?SID=SV_cMGHYuigPfbYTmk

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.eduwith the following information:

1)Your name and section2)Which lab ? (number or title)3)When? (either regular lab time, otherwise specify)

Lab 13Loudspeakers

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 frequencies20 – 500Hz

Tweeter

High-frequencies2 - 20 kHz

Medium

Intermediate500 – 5000 Hz

Woofer

Loudspeakers- lab

Low- pass filter

Tweeter

High- pass filter

Our woofer frequency response to white noise Our 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: http://www.diyaudioandvideo.com/Calculator/XOver/

High-pass

Low-pass

Result:

Woofer

Frequency Response Function

Low- pass filter

Tweeter

High- pass filter

Our woofer frequency response to white noise Our 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 loudspeakerRead 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 playerand listen to the music

through your loudspeaker system!!