Page 100 - Master Handbook of Acoustics

years of exposure to high-level sound in the control room of a recording studio.

Summary

• The outer-ear pinna and the auditory canal, acting as a quarter-wave pipe closed at one end by
the eardrum, contribute acoustical amplification in a region near 3 kHz. Vital speech
frequencies lie in this region.

• The leverage of the ossicles bones of the middle ear and the ratio of areas of the eardrum and
oval window efficiently match the impedance of air to the fluid of the inner ear.
• Waves set up in the inner ear by vibration of the oval window excite the sensory hair cells,
which direct signals to the brain. There is a place effect, the peak of hair cell agitation for

higher frequencies being nearer the oval window and low frequencies at the distal end.
• The area of audibility is bounded by two threshold curves, the threshold of audibility at the soft
extreme and the threshold of feeling or pain at the loud extreme. Our auditory experience
occurs within these two extremes.

• The loudness of tone bursts decreases as the length of the burst is decreased. Bursts greater
than 200 msec have full loudness, indicating a time constant of the ear of about 100 msec.

• Our ears are capable of accurately locating the direction of a source in the horizontal plane. In
a vertical median plane, however, localization ability is less accurate.
• Pitch is a subjective term. Frequency is the associated physical term, and the two have only a
general relationship.

• Subjective timbre or quality of sound and the physical spectrum of the sound are related, but
not equivalent.

• The nonlinearity of the ear generates intermodulation products and spurious harmonics.
• The precedence, or Haas, effect describes the ability of the ear to integrate all sound arriving
within the first 35 msec, giving the perception that the sounds originate from the earlier source,
and making the sounds seem louder.

• Although the ear is generally not effective at evaluating absolute sound parameters, it is very
keen in comparing frequencies, levels, and sound quality.

• Occupational and recreational noises can cause temporary and permanent hearing loss.
Precautionary steps to minimize this type of environmentally caused deafness are
recommended.