The audiogram records the softest level of sound someone detects at each frequency, based on 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 methods (air conduction and bone conduction) to offer the sound to the ear.
Consider the blank audiogram graph below. Along the top of the the graph the numbers vary from 125 to 8000. These numbers reference frequencies, or different pitches of sounds.
The frequency of a sound refers to the frequency of vibration of the sound source. The faster the rate of vibration, the higher 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 has a high-pitch sound, probably measuring around 3,000 to 4,000 Hz.
Normal, healthy, young human ears can hear frequencies as low as 20Hz and up to 20,000Hz. However, audiologists test hearing inside the range 250Hz to 8000Hz because the majority of the sounds of speech happen in this frequency range.
The intensity (loudness) of the sound is measured in decibels (dB). The decibel scale is shown on the side from the เครื่องช่วยฟัง. Audiologists want to use a variety of 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 of the normally-hearing human ear.
The softest sounds that younger 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 in one metre away is about 50 dB HL, though some of the speech sounds will be around 35 to 40 dB HL.
Conversational speech measured from four metres away will likely be quieter, about 35 dB HL, using the softer speech sounds only measuring around 20 dB HL.
Really loud rock concerts can measure 110 to 120 dB HL. Lots of people find sounds over 100 dB HL unpleasantly loud. The incidence of hearing loss increases since we age. Over half the populace aged between 60 and 70 have a hearing difficulties. This increases to more than 70 per cent of those older than 70, and 80 % of the over 80.
Hearing problems among veterans
War veterans will probably have problems with hearing problems due to damage from noise exposure in their service. Hearing is definitely the second most common condition reported by Australian war veterans and war widows, with 55 % reporting hearing difficulties being a current medical condition.
What is masking?
In a hearing test, sound being sent to one ear can sometimes be heard by the opposite ear. This is usually only a problem if there is a change in hearing levels between the two ears. Masking involves fpmaic a special noise into one ear while testing one other ear. Audiologists use masking to discover which ear (cochlea) is hearing the test sound.
Sound heard in a room reaches both ears at very similar levels. When very small children are tested with sounds played away from a loudspeaker, the sound is assumed to be heard through the “better ear”, no matter which ear is nearest the loudspeaker.
Sound delivered by headphones or insert earphones is less apt to be cross-heard. Masking is usually only needed if you have a significant difference in hearing levels between the ears. Sound delivered by way of a bone conductor is readily cross-heard by the opposite ear. Masking is frequently required for bone conduction testing.