Learning in the NVL

The director of the Noise and Vibrations Laboratory, Dr. Koorosh Naghshineh, teaches multiple classes in the areas of noise control and vibration. One of these classes, Engineering Noise Control, has a lab section that is taught in the NVL. Using the equipment available, students learn about the fundamentals of noise, how to measure various acoustic properties, and how to interpret different characteristics of noise. Below are examples of what types of experiments are run for teaching purposes.

Acoustic transmission tube fitted with side branch resonators

In this lab, two different types of resonators, a quarter-wave resonator and a Helmholtz resonator, are used to study how resonators can attenuate noise. An experimental setup (shown below) was created using a transmission tube connected to a speaker at one end and left open on the other. This tube is fitted with each resonator and the sound pressure at the open tube is measured using the Sound Level Meter. Each resonator can be modified in length by moving the plunger up and down. Using principles taught in class, students study how to design a resonator cavity length such that the noise being emitted from the speaker is significantly attenuated. Resonators are used in various industries because of this ability to attenuate unwanted noise.

Sound transmission tube with resonator attached in the center
Acoustic modes of an enclosure
The purpose of this lab is to measure the acoustic modes of a rectangular enclosure. The experimental setup (below) uses three loudspeakers to fully excite the enclosure. Based on the dimensions of the enclosure, the resonant frequencies can be found. Each resonant frequency excites the enclosure in a different way. These are called the modes of the enclosure. By measuring the sound along each axis of the enclosure with a probed microphone, students can see how each frequency excites the enclosure differently. The second part of this lab allows the students to apply the same techniques within the Reverberation Chamber in the lab and experience its acoustic modes. Within this much larger enclosure, students can walk around and physically hear how the room is being excited at each of its resonant frequencies.
 

Clear enclosure for measuring acoustic modes in a space