Pure-tone Audiogram

Measuring Auditory Sensitivity over the Age

João Paulo Teixeira

and Paula Odete Fernandes

1,2

Polytechnic Institute of Bragança, Bragança, Portugal

NECE-UBI, Covilhã, Portugal

Keywords: Pure-tone Audiogram, Hearing Sensitivity, Ear.

Abstract: In this study a pure tone audiogram was developed under the Matlab® mathematical software. Audiogram

measurements were performed to 35 subjects belonging to the female and male and aged between 10 and 88

years old. Some of the subjects with more advanced age had hearing problems over the course of age,

however, none of them was carrying any type of hearing aid. The threshold of the Sound Pressure Level

(SPL) was recorded under 12 pure tones between 125 Hz and 15 kHz. The developed pure-tone audiogram

confirmed its ability to produce auditory brainstem responses (ABRs). Statistical analysis of the SPL

threshold shows no differences between genders and confirms the correlation between age and loss of

sensitivity, more accentuated for higher frequency tones. A strong loss of sensitivity was observed after the

decade of 60 years old.

1 INTRODUCTION

The ear is a receiver associated with the

procurement, conduct, modification, amplification

and analysis of sound waves. The sound waves are

due to molecular vibrations in the air and

characterized by a given frequency and a given

intensity.

At present there are some problems associated

with normal operation of the ear which may result in

a hearing impairment. Deafness, in particular, is one

of the most common symptoms around the world,

reaching all ages, from newborns to the elderly,

through all the existing races, both gender, with a

huge response from the point of view of language

and communication, including, family, cultural,

professional, emotional and even psychological,

with large varied causes (Fransen et al., 2003).

The measure of hearing loss is performed by an

audiogram that submit the subject to stimuli with

different energy or amplitude and records the

threshold of energy necessary to be perceived by

subjects. However, the hearing sensitivity varies

along the frequency. The human hearing apparatus is

more sensitive of the bandwidth between 1 and

5kHz and less sensitive for frequencies below 100

Hz and above 10 kHz.

The literature refer different types of stimuli used

in audiograms, such as clicks, noise masking and

recorded sounds (Stapells and Oates, 1997).

Considering a flat cochlear hearing loss a stimulus

of 1000 Hz filtered clicks was also used (Conijn et

al., 1990). But the pure tone with different

frequencies also has been used by Stapells and

Oates, (Stapells and Oates, 1997).

In this context, we propose small pack software

to produce the pure tone waves and a program for

easily submit the subject to the audiogram test

searching for the threshold of energy of the sound

wave to be listen to. We also present the results of

several subjects and its analysis along the age and

gender considering always the different frequency

ranges.

2 SOUND AND HEARING

The sine wave, which is used in this work are sound

waves that have only one frequency component.

Therefore a sound with the shape of a sine is known

as a pure tone.

In relation to sound waves, they are associated

with changes in pressure called sound pressure and

is commonly expressed as Sound Pressure Level

(SPL) and is measured in decibel (dB). Sound waves

have wavelengths or frequencies of sound, measured

293

Teixeira J. and Fernandes P..

Pure-tone Audiogram - Measuring Auditory Sensitivity over the Age.

DOI: 10.5220/0004328802930296

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2013), pages 293-296

ISBN: 978-989-8565-34-1

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

in cycles per second or Hertz (Hz).

The human ear is sensitive to sound frequencies

between 20 Hz and 20 kHz. The frequencies below

20 Hz are called infra-sound, whilst for frequencies

over 20 kHz, are called the ultrasound (often used in

medicine, more precisely on ultrasound). The

equation 1 presents the measure of the SPL in dB as

a relation between the pressure (P) and the reference

pressure (P

). This reference corresponds to the

threshold of hearing for young persons (aged from

18 to 25 year) at the pure tone frequency of 1000

Hz. This reference corresponds to 20 Pa. For a

sound of pressure P equal to P

the SPL is 0 dB.

20 log ( ) (dB)

SPL



(1)

Fig. 1, represents the relation between SPL over the

frequency, and pressure measurement in dB causing

the same sense of sound volume in young

individuals, in the presence of pure tones (ISO

226:2003).

Figure 1: Equal-loudness contour.

3 AUDIOGRAM

This work has focused on measuring the auditory

sensitivity along frequency and over the years. For

this purpose it was developed an audiogram in

software using the mathematical software

MATLAB®.

The objectives was measuring the threshold of

hearing at 12 different frequencies, ranging from

125Hz down to the 15000Hz, performing the

graphic corresponding to the relation frequency /

amplitude similarly as the graph presented in Fig.1.

For each frequency a pure tone wave produced

by a pure sine wave is created with initial amplitude.

Then, the amplitude is gradually adjusted until the

subject couldn’t perceive sound. The last amplitude

is registered and converted to SPL in dB.

A simple program as developed to produce the

pure tones along the selected frequencies to be used

during the audiogram test. The program intends to

facilitate the task of selecting the SPL to be

presented to the subject until find the threshold of

hearing.

No modulation of amplitude was performed in

contrast with the work presented by Canale in

(Canale et al., 2006). The program asks for the SPL,

then converts the SPL in dB to a linear scale and

produces a 2 second long sine wave signal with the

frequency and the amplitude introduced by the user.

The signal is sent to the audio system to be

presented to the subject. The subject should inform

if the sound was listen in an interactive way to

record the threshold of SPL. The procedure should

be repeated for every frequency tone.

The tests were performed with 35 subjects

belonging to the female and male gender, aged

between 10 and 88 years. Some subjects with more

advanced age had hearing problems over the course

of age, however, none of them was carrying any type

of hearing aid. Importantly, all measures were

performed on privileged and quite rooms and with a

good sound isolation. The subjects were always

placed in front of the computer. The measures were

made on the same computer, so this way all the tests

were performed with the same consistency in the

magnitude of sound waves. Therefore there were no

significant changes in the conditions to collect data

along subject.

The absolute SPL presented to the subject cannot

be determined once the sound card of the computer

has an unknown amplification. In order to deal is

this situation the value of 1 dB was used as a

reference for the threshold of hearing at 125 Hz. We

assumed that the audio system of the computer have

an equally gain along the frequency range (the

frequency response of the computer audio system

must be measured and considered in future

developments). Therefore the absolute values

presented in following section cannot be compared

with the absolute values of Fig 1, only the variation

of sensitivity along frequencies can be compared, by

the shape of the curves of sensitivity.

The same volume level in the computer was kept

during all measures.

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4 RESULTS

First a comparison of each subject within his decade

age was performed for the decades of tens to decade

of eighties. Then a comparison between the averages

of subject of each decade is presented in Fig. 2. The

figure presents the average minimum SPL for each

frequency perceived by the subject of each decade.

As higher is the curve more SPL in need to be

perceived by listener that means less sensitivity.

Therefore, a higher value of SPL in the graphic may

represent a hearing loss at that frequency. Anyhow,

the variation of sensitivity along frequency as

presented in Fig. 1 has to be considered normal.

Figure 2: Hearing sensitivity of each decade.

The decades with lower SPL threshold are the

first four lower decades, ie concerning the decades

10, 20, 40, and finally concerning the decade at 50

years. These first four decades have a hearing

sensitivity pattern similar to the pattern presented in

Figure 1, meaning that the eventual hearing loss may

not be significant. Moreover, the latest age

corresponding to the 60, 70 and 80 decades illustrate

that the higher decades are correlated with a

significant loss of sensitivity. Thus, it is

recommended to the people belonging to this ages

and who have very significant hearing loss, the

possible use of hearing aids in order to aid the

process of hearing (Bento et al., 2010), (Cheng et al.,

2011).

5 STATISTICAL ANALYSIS OF

RESULTS

For all results of inferential analysis a 5% of

significance level was assumed.

Table 1 lists some characteristics of the subjects.

The original sample consisted in 35 subjects, 77,1%

female and 22,9% male. The 6 subjects with clinical

diagnosis of hearing pathology 83,3% are female,

and those who are not a clinical diagnosis of the

pathology 75,9% are female.

Table 1: General Characteristics of Sample (N=35).

subjects

No.

Gender

Female

27 77,1

Male

8 22,9

Age

Decade 10 7 20,0

Decade 20 7 20,0

Decade 30 1 2,9

Decade 40 5 14,3

Decade 50 3 8,6

Decade 60 2 5,7

Decade 70 5 14,3

Decade 80 5 14,3

Clinical diagnosis of Hearing

pathology

With 6 17,1

Without 29 82,9

In order to evaluate differences of SPL among

the eight age decades in each Frequency tones, a

Kruskal-Wallis test was conducted. The Kruskal-

Wallis Test is the nonparametric test equivalent to

the one-way ANOVA and is used when the

assumption of the parametric test have been too

grossly violated (Green and Salkind, 2008). It is

used to test the null hypothesis that all populations

have identical distribution functions against the

alternative hypothesis that at least two of the

samples differ only with respect to location

(median), if at all. Chi-square and p-value have been

used for the comparison. Results are not statistically

significant for the frequency tones of SPL at 125 and

500 Hz (p-value>0.05), it indicates that the groups

are not different from the others. The results of the

analysis for the remaining frequency tones indicates

that there is a significant difference in the SPL

medians, it is the same that at least one of the groups

is different from the others. It can therefore be

concluded that there are differences in the SPL

threshold at frequency tones among the group age

decades.

To evaluate if the median performance of the

SPL along the frequency tones differ for female and

male, the pairwise comparisons was conducted using

the Mann-Whitney U test (nonparametric test),

which yields identical results with the Kruskal-

Wallis test for two independent samples (Green and

Salkind, 2008). Based on the results at the =0.05

level of significance, the results does not provide

Pure-toneAudiogram-MeasuringAuditorySensitivityovertheAge

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statistically significant evidence of a difference

between female and male in median of SPL at all

frequency tones used (p-value>0.05).

The Pearson's correlation was used to find a

correlation between the variables Age decades and

SPL threshold at the frequency tones. According to

the provided results it is possible to say that the

strength association between these two continuous

variables is very high and that the correlation

coefficient is very highly significantly different from

zero (p-value<0.05). For all results produced were

obtained positive coefficients of correlation which

indicate that for every frequency tones the older age

higher is the SPL threshold of hearing. Additionally,

as higher is the frequency tone higher is the Pearson

correlation meaning that for higher frequencies more

correlated are the decade ages with SPL threshold.

This last observation leads to the conclusion that the

lost of sensitivity along age is more effective for

higher frequency tones.

In order to complete the inferential analysis and

see if there is an association between the variables

Clinical Diagnosis of Hearing Pathology and Age

Decade Group (considering two groups: more than

50 years and less than or equal to 50 years), the

Fisher's exact test took place, recommended when

we have two nominal variables (Green and Salkind,

2008). The result indicated that the null hypothesis

can be rejected; so it was possible to say that the

variables are associated.

6 CONCLUSIONS

A pure tone computer software device to produce

auditory brainstem responses was developed and

used to measure the threshold of SPL perceived by

35 subjects in a scale a different frequency tones. A

small group of six individuals had a clinical

diagnosis of hearing pathology, but none of them use

any hearing device.

Despite the small number of individuals used in

the test it was clear that the lost of sensitivity was

higher in older individuals and became more

effective after the decade of 60 years old.

A statistical analysis using SPSS software was

performed. It may be concluded that no significant

differences exist in the frequency tones of 125 and

500 Hz, but there are significant differences in other

frequency tones (250 Hz, 1 kHz, 2 kHz, 3 kHz, 4

kHz, 6 kHz, 8 kHz, 10 kHz, 12 kHz and 15 kHz).

There are no statistically significant evidence of a

difference between female and male of SPL at all

frequency tones used. It was also concluded that

there is a high correlation between SPL threshold

and age within all frequency tones. Despite this

obvious conclusion it was confirmed for all

frequency tones. The statistical analysis also leads us

to the conclusion that as higher is the frequency tone

more correlation there is between sensitivity loss and

age.

Finally, the statistical analysis confirmed a high

correlation between subjects with clinical diagnosis

of hearing loss and the threshold of SPL.

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