Maico MA 53 Operating Instructions Manual

Contents

Maico MA 53 Operating Instructions Manual Manual pdf 18 page image

Operating Instructions MA 53Geba_MA53_e_13a.doc 16 851 430/3 11/114.4 Masking of the opposite earThe basics of masking are explained below. To begin testing immediately,please go directly to 4.4.3 Manual masking.4.4.1 Crossover:When measuring a pure tone audiogram you assume that the measuredhearing threshold is correct. But if you recognize that sound is alsotransmitted through bone conduction over the entire skull it is probable thatthe opposite ear has also received sound. This is called “crossover”.Crossover can also occur when measuring air conduction because a smallamount of air conducted sound is received by the skull and transmitted bybone. Whether the crossover signal can heard by the opposite ear depends onits inner ear function.Relevant to crossover is the sound level which is received by the opposite ear.The difference between the original test signal at the test ear and the receivedsignal at the opposite ear is called “interaural attenuation”.For bone conduction measurement the interaural attenuation is 0 to 15 dB.Bone conduction crossover is therefore possible even with a slight differencein hearing loss between ears.Important: Please advise the patient to tell you in which ear he hears the testsignal. It is thereby easier to detect crossover.4.4.2 Masking theory:To ensure that the patient will not experience crossover you must mask theopposite ear. Masking increases the hearing threshold of the opposite ear.The masking is done with a noise signal which is transmitted by theheadphone. For pure tone audiometry a narrowband noise is used. This noisechanges its center frequency according to the frequency of the test signal.4.4.3 Manual masking:If you have to mask use the common masking rules. See chapter 7 forrecommend literature.Masking is an important part of practical audiometry. It is necessary to befamiliar with this topic to avoid errors which would lead to a wrong diagnosis.For the opposite ear set the receiver selector  or  to AC and the signalselector  or  to NOISE.Adjust the required masking level with the level control knob  or ↕.