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Some of topics included in this course are: Fundamentals of Acoustics, Levels and Decibels, Divergence and Directivity, Hearing, Human Response to Noise, Frequency Analysis, Sound Sources and Fields, Room Acoustics, Sound Power, Noise Barriers, Outdoor Sound Propagation, Helmholtz Resonator and Vibration Control. Key points of this lab manual are: Helmholtz Resonator, Resonant Frequency, Acoustic System, Automobile Mufflers, Rigid Cavity, Resonator Cavity, Theoretical Calculation, Frequency Rang
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ME458 Lab 9 08/17/00 page 1
Objectives:
Background: In this experiment, you will study the dynamics of a Helmholtz resonator. This is an example of a lumped acoustic element (1-D), commonly used in automobile mufflers. They are excellent band-stop acoustic filters. You have probably played with this device many times. Whenever you blow across the top of an open bottle, you are demonstrating a Helmholtz resonator. The resonator consists of a rigid cavity of volume V , neck of area A and length L as shown in the figure below.
The resonance frequency of a Helmholtz resonator (assuming that the physical dimensions are smaller than a wavelength) can be calculated by:
L’ = effective length of the neck
Procedure: Use a loudspeaker driven by a sine wave generator and audio amplifier as the signal source. The source is placed a measured distance from the resonator. A microphone (or sound level meter) is placed in the resonator cavity to measure
ME458 Lab 9 08/17/00 page 2
the response. For four different resonator combinations of neck length and volume, do the following:
Reporting Requirements: Thoroughly document your test procedure, instrumentation, calculations, results, observations and conclusions in a full- length, professional quality report.
In your report: