Minimal Audible Field (MAF) Vs Minimal Audible Pressure (MAP)
Two methods can be used to measure the minimal audible stimulus and therefore the absolute threshold of hearing. Minimal audible field involves the subject sitting in a sound field and stimulus being presented via a loudspeaker. The sound level is then measured at the position of the subjects head with the subject not in the sound field. Minimal audible pressure involves presenting stimuli via headphones or earphones and measuring sound pressure in the subject's ear canal using a very small probe microphone. The two different methods produce different thresholds and minimal audible field thresholds are often 6 to 10 dB better than minimal audible pressure thresholds. It is thought that this difference is due to:
- monaural vs binaural hearing. With minimal audible field both ears are able to detect the stimuli but with minimal audible pressure only one ear is able to detect the stimuli. Binaural hearing is more sensitive than monaural hearing/
- physiological noises heard when ear is occluded by an earphone during minimal audible pressure measurements. When the ear is covered the subject will hear body noises, such as heart beat, and these may have a masking effect.
Minimal audible field and minimal audible pressure are important when considering calibration issues and they also illustrate that the human hearing is most sensitive in the 2–5 kHz range.
Read more about this topic: Absolute Threshold Of Hearing
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