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The text for the class is "Introduction Electroacoustics & Audio Amplifier Design" by W. Marshall Leach, Jr., ISBN 0-7575-0375-6.
Before coming into my office, please turn your cell phone off.
Making the Grade by Physics Professor Kurt Weisenfeld. You can read a student's response here.
Chapters 1 - 12 Formula Sheet Use of this is allowed on quizzes. No additional material may be written on it. Additions or corrections may be made before quizzes.
Electroacoustics Glossary of Symbols. You may use a copy of this on the quizzes. No additional material may be written on it.
The Perception of Pitch. The pitch of a sound wave is closely related to its frequency or periodicity - but the exact nature of that relation remains a mystery. A very interesting article from the 1974 issue of American Scientist published by Sigma Xi.
A paper that describes the design of Zobel matching networks can be read here. You can read see the Mathcad sheet which was used to produce the plots in Figures 7 and 8 in the paper here.
The following links are to the numerical tables from which the vented-box design charts in the book were plotted: QL = 03, QL = 05, QL = 07, QL = 10, QL = 20, QL = infinity
SPICE Netlists: Infinite-Baffle, Closed-Box, Vented-Box
The following pictures show the laboratory setup for measuring the voice-coil impedance of loudspeakers. The basic instrument is the computer controlled Audio Precision Analyzer II.
Picture 01 - Measuring the voice-coil resistance with the ohmmeter.
Picture 02 - Loudspeaker driver connected to the Audio Precision Analyzer II.
Picture 03 - Closeup view of the speaker and analyzer.
Picture 04 - Dr. Allen Robinson making the measurements.
Picture 05 - Screenshot showing the measured magnitude and phase of the impedance.
Picture 06 - The loudspeaker mounted on the compliance test box.
Picture 07 - Dr. Brewer gives the loudspeaker the final test.
Syllabus - Revised 2009/8/26
The GTA for the class is Chris Burdett. His hours in the Tutotial Lab are Thursday from noon to 3:00 p.m. His email address is chrisburdett_at_gatech_dot_edu.
You may work with a partner in submitting homework problems. Only one writeup should be submitted. Be sure to put both names on the cover sheet.
Homework Guidelines (Originally written to minimize student complaints about an ECE 3050 GTA grader.)
The SPICE examples posted for the project use LTSpice. It can be downloaded from the Linear Technology Software Page. LTSpice is widely used by the "do it yourself" audio community.
These are the LTSpice files that will be in the 4th edition of the text. Any of these can be used with the design project, but the numbers must be changed. The crossover network example contains both a woofer and a midrange driven from a single power amplifier with crossover networks. There is an auxiliary RLC circuit that connects to the midrange voice coil for impedance correction. - Infinite Baffle File, Closed-Box File, Vented-Box File, Crossover Example File
The GTA for this semester is Diana Fuertes. Her office hours are Monday 1:00-3:00 and Thursday 11:00-12:00 in Van Leer room C449. Her email address is dianafuertes@gatech.edu.
In the following phases, the math program Mathcad is referred to. You may use any computer math program you wish in place of Mathcad.
Due in class on Wednesday, December 5. Example of a good report.
PRELIMARY REPORT - Due in class on Wednesday, October 25.
FINAL REPORT - Due Friday, November 17.
USE the example plots in the text as a guide for the displayed ranges on the horizontal and vertical axes. For example, do not display a range of more than 30 to 40 dB for the pressure plots. A vertical axis limit of -200 dB to 10 dB is far too great a range. Your plots should appear similar to the ones in the text.
FOR the closed-box simulation, choose a B2 alignment. If the total quality factor of your driver is too large for reasonable closed-box and vented-box systems, you may increase the Bl product to reduce the electrical quality factor. For the plots that compare the measured impedance to the simulated impedance, use the original value of the Bl product. All following simulations must be performed with the increased value of the
TITLE each graph and label the axes appropriately. If more than one plot is on the same graph, identify what each one represents.
INCLUDE all calculations, the SPICE circuits, and the SPICE netlists in your report. Organize the reports with a title page for each section. On these pages, summarize the contents of each section. Include a Summary and Conclusions section at the end of your report.
Below are example Mathcad sheets for calculating the voice-coil inductance parameters. The data is measured for the JBL 2241 15-inch professional driver. There are a total number of 62 frequencies at which the mpedance is measured. You will have to modify the Mathcad sheet for the number of points you obtain from the MLSSA Analyzer. This sheet allows you to calculate the n and the Le in Eq. (6.50) for the impedance of the lossy voice-coil inductance. Because you have so many data points, you should turn off the circled data points on your mathcad plots. Otherwise, you cannot see the curves below the smear of circles.
This paper explains the equations in the mathcad sheet that are used to determine the inductor parameters.
The design of Zobel networks to cancel the high-frequency rise in voice coil impedance due to the inductnce is described in this paper.
Errata and Updates for Course Text - Student assistance in finding errors will be appreciated.
Read this copy of a paper on modeling the voice-coil inductance losses. This paper explains the equations on the mathcad sheet that are used to determine the inductor parameters.
Parameter Calculation Sheet for calculating the small-signal parameters of the driver. You must read Section 12.7 in the text to understand this sheet. The only parts that pertain to the design project are the parts where you calculate fS, QMS, QES, QTS, and VAS.
Example Mathcad sheet for calculating the inductance parameters of the voice-coil. The data is measured for the JBL 2241 15-inch professional driver. There are a total number of 62 frequencies at which the impedance is measured. You will have to modify the Mathcad sheet for the number of points you obtain from the Audio Precision Analyzer, which is 201. This sheet allows you to calculate the n and the Le in Eq. (6.50) for the impedance of the lossy voice-coil inductance. Because you have so many data points, you should turn off the circled data points on your mathcad plots. Otherwise, you cannot see the curves below the smear of circles.
Spring 2000 - Notes on resolving the voice coil inductance parameters from impedance data measured in lab with the MLSSA system. These come from the yet unpublished 3rd edition of the class text.
Spring 2001 - Example Mathcad Sheet for extracting the lossy voice-coil inductance parameters from the measured MLSSA data.
Evaluation Version of AIM SpiceHere is a free version of SPICE that you might like better than PSpice. The evaluation version lets you have 20 active devices (PSpice only allows 10) and 50 nodes in a circuit. The program makes better use of the graphics features of Windows. For example, you can copy plots to the clipboard as metafiles, whereas PSpice only lets you make bitmaps of plots (if you can figure out how to do it). With the graphics post processor, you can scale the plots with the mouse, control the labeling and gridlines, change the axis labels, etc., things that cannot be done with PSpice. You can download the free evaluation version of AIM Spice here.
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