Hearing

ouput level is increased by 3

output level is increased by 6

• 1. To calibrate audiometers
• 2. Assess background levels in audiometric test rooms
• 3. Identify hazardous noise exposure levels

• • Picks up sounds of all frequencies within a certain range
• • Determines the magnitude of the sound in dB SPL

SLM measures overall SPL of sounds picked up by the microphone

De-emphasizes low frequency sounds

• – Set of selectable Band-Pass filters
• – Used to determine dB present for a given frequency bandwidth

Practically linear, virtually no weighting of spectrum in the greatest part of the audible range

some reduction of sound level at very low and very high frequencies

• dramatic reduction of low frequency sound level
• – e.g., sounds of 100 Hz are reduced by about 20 dB

• A and C scales are most commonly used in noise measurement
• A scale used to measure speech sound-closest to human hearing

• a relative measure of sound level
• – There is always a reference value
• – Intensities/Pressure are compared to a standard reference value in the form of a ratio or fraction
• – Physical magnitudes are stated in relation to a value that has meaning to us• See next slide for example

become equal intervals on logarithmic scale