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Unformatted text preview: E85.1801 Fundamentals of Music Technology Instructor: Juan P. Bello Assignment # 3, Directional propagation and sensitivity Full Name:____________________________ NetID:_________________________ Part 1. Demonstration Discussion. Please discuss your observations of microphone directionality and frequency response as related to the class demonstration (max 1 page). Specific Questions to consider: • Why might a dynamic microphone have a different frequency response or sensitivity than a condenser microphone? • What properties of microphones and loud speakers allow them to operate in such close proximity without feedback? Part 2. Practical Experiment Description: For this assignment you are expected to perform a set of small experiments as explained below. Please record the results of the experiments on a short report (max. 3 pages) that also: (i) discusses the reasons for the results you record, (ii) describes any difficulties that you had during the set‐up of the experiments and (iii) provides answers to the questions below. While the experiments can be done in small groups of 2 or 3 people at a time (as long as everyone participates), the reports should be individually written. Important notes: • Earplugs are recommended for this experiment. • If students in the hallway outside the studio are making noise that is interfering with your work, you have the right and duty to politely ask for them to remain quiet during your experiment. Instructions: • The experiments on this assignment can be performed in studios E or F (see 8th floor support desk for studio booking schedules). • For the experiments you will need to borrow the following from the support desk: 1. JBL Eon powered Speaker and Power Cord 2. 1/8” mini to XLR Male adaptor (you may have to ask twice to get this right) 3. 10’ XLR cable. 4. Radioshack Sound Pressure Level (SPL) Meter • • • 5. One person in the group will need to bring a laptop to run the provided signal generating software. Connect the 1/8” mini plug to your computer (via the headphone output) connect the XLR male end to the XLR cable, Connect the cable to the input of the JBL Eon. Connect power to the JBL Eon, turn any and all volume controls to the minimum setting, and switch on the JBL Eon. Start the Software on the computer (follow instructions contained with in the program). Slowly turn up the volume on the JBL until you get a reading on the SPL meter (with the meter set to 70db, A‐weighted, slow response). At the end of the experiments please return all equipment and leave to studio in the same or better condition than how you found it. Experiments: • Once you have established that the sound is completing the circuit from the generator to the speaker. Slowly turn up the volume up on the JBL until you reach 70db SPL on the signal level meter when standing 3 feet from the speaker (with the signal generator set to 1kHz). 1. Move clockwise around the speaker stopping every 45º to measure SPL, record these measurements. 2. Repeat the measurements at the following frequencies: 100 Hz, 3kHz and 8kHz. 3. Plot these measurements on a graph of dB versus degrees for each of the frequencies. (See the book for formatting example). 4. If you are having difficulty with your readings try: • Testing at additional frequencies: 250hz, 600hz, 2kHz, 4kHz, 9kHz • Moving the speaker from the stand to the floor, and repeat Questions: How did the dB SPL change with rotation of the speaker if at all? What is the expected change in intensity? How does the intensity change with regards to rotation at different Frequencies? Which specific frequencies did you use for your graphs? Did any frequencies produce readings that differed greatly from your expectations? Report: Answer each of the above questions as complete thoughts in formal English. Analyze and discuss the results of the experiments, trying always to relate your findings and observations to the theory discussed in class and the demo sessions. ...
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- Fall '09