Speaker Location

Different testing situations demand certain loud speaker locations.  Two common test situations are the measurement of functional gain on hearing aids and the evaluation of young children by visual reinforcement audiometry.  The diagram below illustrated a common configuration for loud speaker location.  

Letters A-D represent speaker location

Ideally, speakers should be placed in a corner (as illustrated above) to reduce standing waves and encourage distribution of the signal in the diffuse field.  Two speakers are necessary for testing localization abilities.  

Young children are often tested in the sound field using visual reinforcement audiometry.  When testing children, the loudspeakers vertical placement needs to be lower so that they are at the child's ear/head level.  More specifically, the high frequency speaker cones should be at the level of the subject's ear, so that the directional nature of the high frequencies does not create a problem.   

The picture below illustrates a situation where the sound field is being calibrated.  Notice that the speaker height relative to the chair is quite low.  If an average sized adult were to sit in the chair occupied by the sound level meter, his/her head would be higher than the speaker height.  This room configuration therefore is primarily used to test children by VRA.  For facilities that have chairs with adjustable height, the speakers can be set at a greater height.         

A condenser microphone attached to the sound level meter is placed at least 1 meter in front of the face of the loud speaker (as shown above), taking care to account for the angle of incidence of the signal from the speaker to conform to the characteristics of the measuring microphone.  The microphone should also be 0.6 meters away from any wall of the booth.   

Also notice that there is another chair present in the sound booth during the calibration.  This is alright, as long as during normal test condition, the chair remain in the room.  Removing the chair during testing can change the apparent response characteristics of the speaker by as much as 5 - 10 dB.   

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