The audiogram records the softest level of sound a person detects at each frequency, in accordance with specific test criteria. These detectable amounts of sound are called the person’s hearing thresholds. During a hearing test, the audiologist will usually try to obtain thresholds for a number of different frequencies in each ear, often using various ways (air conduction and bone conduction) to deliver the sound to the ear.
Consider the blank audiogram graph below. Along the top of the the graph the numbers range from 125 to 8000. These numbers make reference to frequencies, or different pitches of sounds.
The regularity of any sound refers back to the frequency of vibration from the sound source. The faster the speed of vibration, the larger the frequency in the sound. Sound frequency is generally measured in Hertz (Hz). A 250 Hertz (250Hz) tone sounds like a deep, low-pitched horn. A tiny, tinkling bell features a high-pitch sound, probably measuring around 3,000 to 4,000 Hz.
Normal, healthy, young human ears can hear frequencies as little as 20Hz and as much as 20,000Hz. However, audiologists test hearing in the range 250Hz to 8000Hz because the majority of the sounds of speech appear in this frequency range.
The intensity (loudness) of the sound is measured in decibels (dB). The decibel scale is shown down the side from the เครื่องช่วยฟัง. Audiologists need to use a number of different decibel scales, for the way the sound is measured. For hearing tests, sound is normally measured in decibels of Hearing Level (dB HL). This decibel scale reflects the sensitivity from the normally-hearing human ear.
The softest sounds that young people with normal hearing can detect in ideal listening conditions, is between zero and 20 ( – 20) dB HL, over the frequency range.
Conversational speech measured from a single metre away is approximately 50 dB HL, though some of the speech sounds is going to be around 35 to 40 dB HL.
Conversational speech measured from four metres away will be quieter, about 35 dB HL, with all the softer speech sounds only measuring around 20 dB HL.
Really loud rock concerts can measure 110 to 120 dB HL. Many people find sounds over 100 dB HL unpleasantly loud. The incidence of hearing difficulties increases as we get older. Over half the populace aged between 60 and 70 possess a hearing loss. This increases to greater than 70 percent of these over the age of 70, and 80 per cent of the older than 80.
Hearing difficulties among veterans
War veterans are likely to have problems with hearing problems because of damage from noise exposure throughout their service. Hearing is the second most common medical condition reported by Australian war veterans and war widows, with 55 % reporting hearing loss as being a current condition.
Precisely what is masking?
In a hearing test, sound being delivered to one ear can sometimes be heard through the opposite ear. This is usually only a concern when there is a positive change in hearing levels involving the two ears. Masking involves fpmaic a special noise into one ear while testing another ear. Audiologists use masking to find out which ear (cochlea) is hearing the exam sound.
Sound heard in a room reaches both ears at very similar levels. When very young children are tested with sounds played from a loudspeaker, the sound is assumed to be heard by the “better ear”, regardless of which ear is nearest the loudspeaker.
Sound delivered by headphones or insert earphones is less likely to be cross-heard. Masking is usually only needed when there is a huge difference in hearing levels in between the ears. Sound delivered by way of a bone conductor is definitely cross-heard through the opposite ear. Masking is frequently necessary for bone conduction testing.