Advanced Vibrations and Acoustics

Topic - Audiometry report

Task 1 - Hearing characteristics of the human ear.

Learning outcome 1: Measure noise and vibration using appropriate equipment and techniques and technically appraise experimental methods.

Learning outcome 2: To enable students to analyse, predict and evaluate the generation, propagation and effects of sound waves and vibrations on mechanical systems, humans and the environment.

Aim: To investigate the hearing threshold characteristics of the human ear and methods of hearing measurement.

Audiometry testing: An audiometry test uses a pure tone to measure the least audible sound that a person can hear for specific frequencies selected. During the test, the person wears earphones and is subjected to a pure sound tone in one ear at a time. The loudness of sound is measured in decibels (dB). The tone of sound is measured within a frequency range between 50 and 10,000 Hz or higher depending upon the specific purpose of the test.

To identify the Threshold level of hearing of a person an Audiometry measurement system is needed. This comprises of a sound booth (sound enclosure), audiometry headphones and a control device. The function of the sound booth is to provide a background noise level of ideally 0dB. The role of audiometry headphones is to provide a pure sound tone in either the left or right ear. The function of the control device is twofold; firstly to select and send the sound level and the frequency of the pure tone and secondly to aid communication between the person undergoing the test and the technician conducting this.

Communication: When a pure tone at a selected level and frequency is sent to either ear of the person in the audiometric sound booth (sound enclosure), the person confirms the tone can be heard by pressing a switch inside the booth. This activates a light outside the booth which the technician conducting the test will see. A green light indicates the person can hear the level of the pure tone at that selected frequency.

When a pure tone is not detected by the person undergoing the test the switch will be deactivated and a red light will be present on the control unit. The sound level of the pure tone can also be adjusted by the technician; in the data collected and given in table 1a and 1b (Appendix 1) in dB. This is done in 10dB increments until the threshold of hearing for the pure tone has been identified and noted. The lowest level of the pure tone that can be heard by ear is known as the threshold of hearing at that selected frequency. In this task, hearing threshold data has been collected by completing audiometric testing for 7 young male participants ( age variation is between 23 and 25 years old) at following frequencies:125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz, 4000Hz and 8000Hz. Threshold levels for each ear at these frequencies for each person are shown in table 1a (left ear) and 1b (right ear) of Appendix1.

What you need to do in this task
Data Analysis: To investigate the characteristics of the human ear and hearing measurement techniques, you will need to plot the relationship between the threshold level and frequency of each person. The resulting relationship should be validated using a suitable source and thereafter analysis comparatively should centre upon establishing reasons for discrepancies present in the trends of the data plotted.

Furthermore, your investigation should also consider the factors that affect the shape of the graph plotted (audiogram) and explain why the shape is of this form. Research: To inform your work you will need to carry out research which includes, at the very least, the following topics:

• Hearing Threshold test methods
• The working of the human ear
• Types of hearing loss and their causes.

Attachment:- lab-data.rar